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Detection signal amplification strategies at nanomaterial-based photoelectrochemical biosensors
Abstract
This review focusses on unique material modification and signal amplification strategies reported in developing photoelectrochemical (PEC) biosensors with utmost sensitivity and selectivity. These successes have partly been achieved by applying photoactive materials that significantly circumvent major limitations including poor absorption of visible light, severe aggregation of nanostructures, easy charge recombination and low conductivity. In addition, several signal enhancement techniques were also demonstrated to have effectively improved the detection performance of PEC biosensors. Accordingly, we have begun this review with a systematic introduction of the concept, working principle, and characteristics of PEC biosensors. This was followed by a discussion of a range of material modification techniques, including quantum dot modification, metal/non-metal ion doping, formation of heterojunctions and Z-scheme composites, used in construction of PEC biosensors. Various signal amplification strategies including quantum dot sensitisation, application of electron donors, energy transfer effect, steric hindrances of biomolecules, and exfoliation of biomolecules from sensing surfaces are also presented in this review. Wherever possible, we have referred to relevant examples to explain and illustrate the corresponding working mechanism and effectiveness of the nanomaterials. Therefore, this review is aimed at providing an overall view on the current trend in material modification and signal amplification strategies for PEC biosensor development, which will aid in stimulating ideas for future progress in this field.
... PEC biosensor generally consists of three indispensable elements: (1) light source for excitation, (2) WE, CE, and electrolytic solution/wastewater as detection system, and (3) signal acquisition system. It works on the principle of converting a photo to an electrical signal, which generates a photocurrent signal after irradiation of light to the working electrode (photoactive material) [72,73], as depicted in Fig. 11.4A. The overall mechanism involved in the working of PEC biosensors involves (1) light adsorption by the photoactive material, (2) generation of photoexcited carriers, i.e., electrons (e À ) and holes (h þ ), and (3) charge separation to the respective terminals (e À on working electrode and h þ to the electrolyte) [26,74]. ...
... Subsequently, produced photo e À injects from the CB of photoactive material to the conductive working electrode. Concurrently, high energy photo h þ is scavenged by the targeted biomolecules/pollutants present in the electrolytic solution/wastewater and oxidizes the targeted biomolecules, which contributes an electron to the photoactive material [72]. However, oxidation of biomolecules depends on the kinetic energy of photo h þ ; the oxidation potential of target analyte present in electrolyte should be less than VB energy of bioactive material for effective photocatalytic oxidation. ...
... Several salient features of PEC biosensor contribute to its improved performance such as the following: (1) it combines three different aspects including photocatalysis, biocatalysis, and electrocatalysis, which synergistically contribute their advantages in terms of characteristically fast response, miniaturization feasibility, and high sensitivity, (2) exploration of specific biomolecules for interaction with targeted analyte lead to high selectivity and sensitivity in PEC biosensors, and (3) separation of excitation source (light) from recognition signal (electric current) contributes to low background signal and high sensitivity [72,73]. ...
Water quality can affect all aspects of life, such as food, energy, health, and the economy. Early detection of threats from polluted water can protect all aspects of life and habitat degradation. Traditional wastewater monitoring techniques are sophisticated, require rapid sampling, have a high cost, and are time-consuming; it also fails to monitor timely change in pollutant concentration. The development of biosensors has attracted substantial attention for their precise monitoring, high sensitivity, simplicity, reliability, low cost, and online monitoring. This chapter provides a general overview of a biosensor used for online monitoring of several pollutants including toxic pollutants, nitrogen, and organic pollutants present in wastewater, as well as monitoring of infectious disease outbreaks through wastewater. Furthermore, the chapter includes future trends and perspectives of biosensors in wastewater.
... In PEC analysis, the photoactive material on the sensor surface is stimulated by incident light to generate electron-hole pairs, and then a certain intensity of photovoltage is generated due to the separation of electrons and holes, resulting in photocurrent as the detection signal. The biomolecules fixed on the photoactive material are usually used as biometric elements to capture the target analyte and/or as FOOD SAFETY AND HEALTH -79 amplification elements (Yang, Zhang, et al., 2020). Therefore, photoactive materials are one of the cores of building an excellent PEC platform as stable and powerful photocurrent is the precondition for exciting the remarkable performance of PEC sensors. ...
Food contaminants have consistently posed a serious threat to human health and have caused various food safety problems. The most common techniques currently used for the detection of food contaminants, include instrumental and immunoassay methods; however, these traditional methods have shown some limitations when applied to the analysis of food contaminants. Therefore, in recent years, more and more researchers have been devoted to the development of rapid, reliable, sensitive, and suitable detection techniques for the detection of food contaminants in food matrices. In this review, we first classify the analytical methods proposed in recent years into colorimetric methods, fluorescence methods, photoelectrochemical methods, electrochemical methods, nucleic acid amplification methods, and other methods, and illustrate their detection principles. In addition, the paper highlights the strategies and recent research advances for each method through typical application examples. Finally, the future perspectives of these analytical methods are presented. We hope that this review will provide researchers with valuable insights to guide the sensitive detection of food contaminants.
... Amplification techniques, such as enzymatic reactions or target-induced catalytic activities, can significantly amplify the signal response, enabling the detection of analytes at ultra-low concentrations. This is particularly crucial in medical diagnostics, where early detection of disease biomarkers can be lifesaving [63,64]. Real-time monitoring capabilities are highly desirable in many sensing applications, especially in dynamic and timesensitive environments. ...
Bacillus anthracis, a formidable Gram-positive bacterium, stands as one of the most notorious and enigmatic pathogens known to mankind. Its distinct characteristics have captured the attention of scientists and the collective human imagination for centuries. This bacterium is responsible for causing Anthrax, one of the world's most feared infectious diseases. Substantial endeavors have been undertaken since the 2001 anthrax attacks in the United States to develop effective methods for anthrax spore detection. These initiatives aim to swiftly and accurately identify the presence of anthrax spores to prevent the spread of the disease. The detection of Bacillus anthracis spores plays a critical role in maintaining biosecurity and preventing disease outbreaks. These spores contain a unique component called dipicolinic acid (DPA), which accounts for approximately 5–15% of the spore's dry mass. DPA is exclusively found in bacterial spores and serves as an ideal biomarker for the detection of Bacillus anthracis spores. Therefore, accurate detection of DPA plays a crucial role in understanding spore formation and bacterial identification. This review article summarized various types of nanomaterials, including metallic nanoparticles, carbon dots, quantum dots, metal–organic frameworks and other materials, that have been used for colorimetric and fluorescent sensing of DPA. Furthermore, this review article also provides information about the sensing mechanism, detection limit, selectivity, pH and practical applications of the sensors reported in the literature. We hope that this article will inspire interest in the promising research area of nanomaterials-based sensors for the recognition of DPA.
Graphical abstract
... A PEC biosensor is a recently developed technology based on the combination of PEC reaction and specific recognition process [60]. PEC biosensors have evolved in the recent past as devices for food safety, biomolecular assays, medical health, environmental testing, and new drug research [61]. This type of biosensor typically has three components: light source for excitation, detection system with electrolyte and electrodes, and a signal acquisition system. ...
The presence of emerging contaminants (ECs) can pose human health risks in diverse forms such as endocrine disruption, tumors, reproductive failure, and fetal damage. It is thus important to develop sensitive techniques to monitor the levels of ECs in foodstuffs with accuracy and selectivity. In recent years, aptasensors have emerged as bioprobes for the detection of diverse ECs with many advantages, especially for the food safety applications. To contextualize such developments, this review provides an extensive description of aptasensors developed for the monitoring of ECs in foodstuffs in the recent past, with emphasis on electrochemical, optical, and photoelectrochemical aptasensors. Further, performance evaluation has also been made between various aptasensors in terms of the basic quality assurance parameters. This review delineates a comprehensive analysis of the aptasensors for the mass-scale detection of ECs along with the discussions on their merits/demerits and future challenges.
... Aimed at this issue, extensive research has been devoted to designing efficient photoelectrodes. 13,14 In this respect, n-type semiconductors with electrons as the major charge carriers are used to construct a photoanode. However, among the problems encountered, an unstable output signal and poor anti-interference ability often arise from the oxidation of reducing agents in real-life biological samples by photogenerated holes. ...
Cardiac troponin I (cTnI) is an extremely sensitive biomarker for early indication of acute myocardial infarction (AMI). However, it still remains a tough challenge for many newly developed cTnI biosensors to achieve superior sensing performance including high sensitivity, rapid detection, and resistance to interference in clinical serum samples. Herein, a novel photocathodic immunosensor toward cTnI sensing has been successfully developed by designing a unique S-scheme heterojunction based on the porphyrin-based covalent organic frameworks (p-COFs) and p-type silicon nanowire arrays (p-SiNWs). In the novel heterojunction, the p-SiNWs are employed as the photocathode platform to acquire a strong photocurrent response. The in situ-grown p-COFs can accelerate the spatial migration rate of charge carriers by forming proper band alignment with the p-SiNWs. The crystalline π-conjugated network of p-COFs with abundant amino groups also promotes the electron transfer and anti-cTnI immobilizing process. The developed photocathodic immunosensor demonstrates a broad detection range of 5 pg/mL-10 ng/mL and a low limit of detection (LOD) of 1.36 pg/mL in clinical serum samples. Besides, the PEC sensor owns several advantages including good stability and superior anti-interference ability. By comparing our results with that of the commercial ELISA method, the relative deviations range from 0.06 to 0.18% (n = 3), and the recovery rates range from 95.4 to 109.5%. This work displays a novel strategy to design efficient and stable PEC sensing platforms for cTnI detection in real-life serums and provides guidance in future clinical diagnosis.
... Appropriately amplifying the detection signal is necessary. For example, Yang et al. (2020), reviewed detection signal amplification strategies for nanomaterial-based photoelectrochemical (PEC) biosensors, and put forward PEC instruments that are simpler, more cost-effective, with higher analytical detection performance and easier miniaturization. In addition, the PEC sensors can reduce background signals, and have higher sensitivity than conventional electrochemical methods. ...
The outbreak of the coronavirus (COVID-19) has heightened awareness of the importance of quick and easy testing. The convenience, speed, and timely results from point-of-care testing (POCT) in all vitro diagnostic devices has drawn the strong interest of researchers. However, there are still many challenges in the development of POCT devices, such as the pretreatment of samples, detection sensitivity, specificity, and so on. It is anticipated that the unique properties of nanomaterials, e.g., their magnetic, optical, thermal, and electrically conductive features, will address the deficiencies that currently exist in POCT devices. In this review, we mainly analyze the work processes of POCT devices, especially in nucleic acid detection, and summarize how novel nanomaterials used in various aspects of POCT products can improve performance, with the ultimate aims of offering new ideas for the application of nanomaterials and the overall development of POCT devices.
... As shown in Scheme 5, on irradiating the photoactive material with light having energy equal to or greater than its band gap, the following process takes place. (a) a hole (h + ) is generated on moving of an electron (e À ) from the VB to the CB; (b) the photocurrent and photovoltage is generated by splitting and transporting the generated e À /h + pairs to the electrode surface and electrolyte; (c) a change in photocurrent or photovoltage is occurred when the target analytes influence the charge separation and/or migration processes [175][176][177]. Since the input source of light is completely separated from the output electrical signal, the PEC sensor offers excellent sensitivity and minimized background noise whereas the output electronic signals garnered PEC method with the attributes of minimized equipment and low cost [23]. ...
The great progresses witnessed in the last decade for the rational design of the graphitic carbon nitride (g-C3N4) have warranted its successful use in applications including sensing, photocatalysis, electromagnetic shielding and energy storage devices. There have been multiple studies for g-C3N4 (or g-CN) nanostructures that have underlined the substantial research as a photocatalyst and electrode material in energy devices, while no such in-depth study, on the other hand, went into detail about the g-CN based sensors, their underlying problems regarding the transduction principles, and sensitivity/selectivity issues towards various analytes. Although in its nascent stage, the g-CN nanostructures have made the detection possible in almost all environmental entities (land, air, and water), e.g., biomolecules (protein, glucose, melamine, amino acids) and engineered compounds (drugs, antibiotics, explosives), yet a systematic study summarizing the merits/demerits for g-CN based sensors is still missing. This review gives a detailed overview and summarizes the challenges while simultaneously highlights the key insights in the exciting field of sensors. Researchers working in the sensor domain will undoubtedly benefit from this review, as it will provide new perspectives into the intriguing world of g-CN material which has emerged as a new sensing platform that is at-par to other functional materials discussed in the literature.
... Nevertheless, some of the analytes tend to be low in the early stages of diseases. Therefore, it is considerable to employ signal amplification strategies into the PEC system [14][15][16]. To date, multifarious signal amplification strategies have been put forward for PEC immunoassay to enhance sensitivity, such as enzymemediated catalytic [17], energy transfer [18], chemical redox cycling [19], nano-material labels [20], and other strategies. ...
Nowadays, the epidemic, employment, and academic pressures are seriously affecting our physical and mental health. Herein, we designed a magneto-controlled photoelectrochemical immunosensor for noninvasive monitoring of salivary cortisol regarded as a pressure biomarker. A competitive immunoassay model was established by coupling bovine serum albumin-cortisol modified magnetic beads (MB-BSA-cortisol) with silver nanoclusters (Ag NCs)-labelled anti-cortisol antibody, and quantity analysis was operated by photoelectrochemical measurement of the CdS/Au electrode as an ion-exchange platform. Accompanying the formation of immune complexes, the carried Ag NCs were readily dissolved with nitric acid to produce abundant silver ions, which transferred to the electrode for ion-exchange reaction with CdS quantum dots to produce Ag2S, a new electron-hole capture site, leading to a decrease in the photocurrent intensity. The photocurrent signal gradually recovered with the increase of concentration of target cortisol, acquiring the signal-on mode competitive immunosensing system, which is propitious to the detection of small molecules. Within optimal conditions, this sensor had a satisfactory linear relationship in the range of 0.0001-100 ng mL-1 with favorable repeatability, specificity, and acceptable method accuracy. The detection limit was as low as 0.06 pg mL-1. In addition, this strategy provided new thought for the test of other small-molecule analytes and immunosensor applied in the complex biological system.
Human health and ecology are seriously threatened by harmful environmental contaminants. It is essential to develop efficient and simple methods for their detection. Environmental pollutants can be detected using photoelectrochemical (PEC) detection technologies. The key ingredient in the PEC sensing system is the photoactive material. Due to the unique characteristics, such as a large surface area, enhanced exposure of active sites, and effective mass capture and diffusion, porous materials have been regarded as ideal sensing materials for the construction of PEC sensors. Extensive efforts have been devoted to the development and modification of PEC sensors based on porous materials. However, a review of the relationship between detection performance and the structure of porous materials is still lacking. In this work, we present an overview of PEC sensors based on porous materials. A number of typical porous materials are introduced separately, and their applications in PEC detection of different types of environmental pollutants are also discussed. More importantly, special attention has been paid to how the porous material's structure affects aspects like sensitivity, selectivity, and detection limits of the associated PEC sensor. In addition, future research perspectives in the area of PEC sensors based on porous materials are presented.
Pesticides have become an integral part of modern agricultural practices, but their widespread use poses a significant threat to human health. As such, there is a pressing need to develop effective methods for detecting pesticides in food and environmental samples. Traditional chromatography methods and common rapid detection methods cannot satisfy accuracy, portability, long storage time, and solution stability at the same time. In recent years, photoelectrochemical (PEC) sensing technology has gained attention as a promising approach for detecting various pesticides due to its salient advantages, including high sensitivity, low cost, simple operation, fast response, and easy miniaturization, thus becoming a competitive candidate for real-time and on-site monitoring of pesticide levels. This review provides an overview of the recent advancements in PEC methods for pesticide detection and their applications in ensuring food and environmental safety, with a focus on the categories of photoactive materials, from single semiconductor to semiconductor–semiconductor heterojunction, and signaling mechanisms of PEC sensing platforms, including oxidation of pesticides, steric hindrance, generation/decrease in sacrificial agents, and introduction/release of photoactive materials. Additionally, this review will offer insights into future prospects and confrontations, thereby contributing novel perspectives to this evolving domain.
In recent years, photoelectrochemical (PEC) sensors have attracted much attention due to their inherent advantages, such as ease of operation, high sensitivity, and structural diversity. Compared with conventional PEC detection methods, self‐illuminated PEC sensors do not require an external light source, which makes them more attractive in terms of instrument miniaturization and simplified operation. Chemiluminescence (CL), a straightforward and efficient excitation source, can be harnessed for PEC sensors. In this review, we provide a summary on the recently reported chemiluminescence‐driven PEC sensors. Initially, we briefly describe the current chemiluminescent systems employed in PEC sensors, including luminol and peroxyoxalate CL systems. Subsequently, the CL‐exciting modes and the design strategies for self‐excited PEC sensors are explored. The subsequent sections of the paper predominantly focus on discussing the applications of such PEC sensors in the detection of various target analytes. Furthermore, future prospects for advancing these PEC sensors are discussed.
A photo-driven self-powered aptasensor was constructed based on a matching capacitor and the ZnIn2S4/Ti3C2 heterojunction as the photoanode and Cu2O as the photocathode in a dual-photoelectrode sensing matrix for multiple signal amplification for the ultrasensitive detection of microcystin-RR (MC-RR). The introduction of Ti3C2 MXene nanosheets on the photoanode surface can not only accelerate the transfer and separation of photoinduced electron/hole pairs, thus enhancing the output signal of the photo-driven self-powered system, but also provide a larger specific surface area for the immobilization of the bio-recognition unit aptamer. More importantly, for a portable and miniaturized device, a micro-workstation with the size of a universal serial bus (USB) disk and a novel short-circuit current access was proposed to capture the instantaneous output electrical signal for real-time data tracking. In such a way, a sensitivity of 2.7 mA pM-1 was achieved when the matching capacitor was integrated into the self-powered system, which was 22 times that without a capacitor. After the interaction between MC-RR and the corresponding aptamer, a 'signal-off' detection configuration was formed via the steric hindrance effect. Therefore, such a multiple signal amplification system realized the ultrasensitive and selective determination of MC-RR successfully. Under optimal conditions, the linear range of the self-powered aptasensor was 0.1 to 100 pM and the detection limit was 0.033 pM (S/N = 3). The aptasensor was applied to the detection of MC-RR in fish, exhibiting good reproducibility (≈3.88%), paving the way for detecting microcystins in real-life samples.
Rapid and specific assaying of molecules that report on a pathophysiological condition, environmental pollution, or drug concentration is pivotal for establishing efficient and accurate diagnostic systems. One of the main components required for the construction of these systems is the recognition element (receptor) that can identify target analytes. Oligonucleotide switching structures, or aptamers, have been widely studied as selective receptors that can precisely identify targets in different analyzed matrices with minimal interference from other components in an antibody-like recognition process. These aptasensors, especially when integrated into sensing platforms, enable a multitude of sensors that can outperform antibody-based sensors in terms of flexibility of the sensing strategy and ease of deployment to areas with limited resources. Research into compounds that efficiently enhance signal transduction and provide a suitable platform for conjugating aptamers has gained huge momentum over the past decade. The multifaceted nature of conjugated polymers (CPs), notably their versatile electrical and optical properties, endows them with a broad range of potential applications in optical, electrical, and electrochemical signal transduction. Despite the substantial body of research demonstrating the enhanced performance of sensing devices using doped or nanostructure-embedded CPs, few reviews are available that specifically describe the use of conjugated polymers in aptasensing. The purpose of this review is to bridge this gap and provide a comprehensive description of a variety of CPs, from a historical viewpoint, underpinning their specific characteristics and demonstrating the advances in biosensors associated with the use of these conjugated polymers.
Printable biosensors have gained numerous exciting advancements towards downstream applications in fundamental biomedical research, healthcare, food safety, environmental monitoring and governance, and to name a few. Particularly, paper-based printable biosensors have gained rising popularity in providing affordable platforms due to their merits, such as cost-effective, accurate, simple, and efficient detection of diseases for clinical diagnosis. In addition to advantages and opportunities in point-of-care detection, printable biosensors are also facing challenges. Herein, this review aims to provide a systematic summary of the development of printable biosensors, with a special focus on paper-based printable biosensors. Different types of substrates for printable biosensors are highlighted with a focus on paper substrates which have superior properties like low-cost, simple, flexible, lightweight, recyclable, etc. In addition, current printing technologies to fabricate paper-based sensors, including wax printing, photolithography, screen printing, inkjet printing, and laser printing summarize, are discussed, together with strategies for biomolecular fabrication on substrates and transducers. Finally, we also discuss the challenges and possible future perspectives, hoping to provide researchers and clinicians with informative insights into paper-based printable biosensors for smart and effective point-of-care detection.
Photoelectrochemical (PEC) enzymatic biosensors have attracted widespread attention for their specificity and sensitivity, but the charge migration between an enzyme and a semiconductor remains uncertain. In this work, horseradish peroxidase (HRP) was successfully immobilized on ionic liquid-functioned Cu@Cu2O (IL-Cu@Cu2O) aerogels to boost charge transfer and an interfacial redox reaction. The photogenerated electrons flow from the conduction band of Cu2O to HRP under the assistance of Cu and are subsequently captured by [Fe(CN)6]3- in the electrolyte, which boosts the PEC response. The improved interfacial catalytic ability after the immobilization of HRP is proved by the enhanced redox ability under light irradiation. Benefiting from the excellent PEC activity and catalysis reaction of IL-Cu@Cu2O@HRP, an immunoassay platform was constructed for sensing prostate-specific antigens, which presents a wide detection range and a low limit of detection. An in-depth understanding of the direct electronic communication between a photoactive material and an enzyme for boosted charge transfer and interfacial catalysis provides a new view for the design of advanced PEC sensing platforms.
Photoelectrochemical sensors have outstanding advantages including high sensitivity and miniaturization for outdoor use. Recently, perovskite quantum dots have attracted significant attention due to their high photoluminescence quantum yield. Nonetheless, there is still a strong need to improve their performance in challenging aqueous biological applications. In this paper, based on the molecularly imprinted polymer encapsulation of CsPbBr3 perovskite quantum dot/TiO2 inverse opal heterojunction structures, linear photoelectrochemical detection of cholesterol in aqueous solution was obtained without the involvement of an enzyme. The attenuation of photocurrent intensity under intermittent irradiation within 900 s (45 on/off cycles) was only 8.6%, demonstrating the superior stability of CsPbBr3 based sensor here. At the same time, the minimum detection limit of 1.22 × 10-9 mol L-1 in buffer conditions was lower than that reported for cholesterol photoelectric sensors. It has also been shown that the photoelectrochemical sensor of CsPbBr3 here outperformed that of CH3NH3PbBr3, which is another important member of the perovskite family. Finally, the proposed photoelectrochemical sensor platform was successfully applied in the determination of cholesterol in challenging serum with satisfactory recovery. The synergism among CsPbBr3 perovskite quantum dots, TiO2 inverse opal structure and imprinted polymer has led to greatly improved water stability, super selectivity and sensitivity, thus promoting the development of perovskite-based biological sensors.
A novel and highly sensitive upconversion fluorescence and colorimetric dual readout iodate (IO3-) nanosensor system was constructed by using both the outstanding optical performance of NaYF4:Yb, Tm upconversion nanoparticles (UCNPs) and the analyte-triggered cascade signal amplification (CSA) technique. The construction of the sensing system consisted of three processes. First, IO3- oxidized o-phenylenediamine (OPD) to diaminophenazine (OPDox), while IO3- was reduced to I2. Second, the generated I2 can further oxidize OPD to OPDox. This mechanism has been verified by 1H NMR spectra titration analysis and HRMS measurement, which effectively improves the selectivity and sensitivity of the measurement of IO3-. Third, the generated OPDox can effectively quench the fluorescence of UCNPs via the inner filter effect (IFE), realize analyte-triggered CSA, and allow quantitative determination of IO3-. Under the optimized conditions, the fluorescence quenching efficiency showed a good linear relationship to IO3- concentration in the range of 0.06-100 μM, and the detection limit reached 0.026 μM (3RSD/slope). Moreover, this method was applied to detect IO3- in table salt samples, yielding satisfactory determination results with excellent recoveries (95.5-105%) and high precision (RSD <5.5%). These results suggest that the dual-readout sensing strategy with well-defined response mechanisms has promising application prospects in physiological and pathological studies.
Breast cancer is the most common malignant tumor in women, which seriously threatens the life and health of patients. Therefore, facile and sensitive detection of human breast cancer cells is crucial for cancer diagnosis. In this work, plum-branched CdS/Bi2S3 heterostructures (CdS/Bi2S3 HSs) were synthesized under hydrothermal condition, whose photoelectrochemical (PEC) property and biocompatibility were scrutinously investigated. In parallel, a signal amplification strategy was designed based on immune recognition between epidermal growth factor receptor (EGFR) overexpressed on membrane of breast cancer cells MDA-MB-231 and its aptamer. Integration of the above together, a highly sensitive PEC cytosensor was developed for analysis of target MDA-MB-231 cells, exhibiting a wider linear range of 1 × 102 ∼ 3 × 105 cells mL-1 with a limit of detection (LOD) down to 6 cells mL-1 (S/N = 3). Further, the biosensor was explored for anticancer drug (e.g., dacomitinib) screening by monitoring the variations in the PEC signals of the expressed EGFR upon drug stimulation. The obtained CdS/Bi2S3 HSs are identified as promising and feasible photoactive material for determination of cancer cells and drug screening in clinic and related research.
As an important tumor marker, the ultra-sensitive detection of low-abundance microRNAs provides important data support for early warning of tumors. Herein, taking microRNA-141 as the target model, a novel enzyme-free semi-homogeneous photoelectrochemical (SHO-PEC) biosensor was designed by entropy-driven three-dimensional (3D) DNA walker with exponential signal amplification, magnetic enrichment and separation of pseudo-targets, bridged [email protected] quantum dots to promote photocathodic current enhancement, and in situ generated silver nanoparticles (NPs) to accelerate charge separation. In this protocol, ZnS shell passivates the surface defects of the soft core CdTe, introducing considerable strain that causes electrons to extend towards the shell, which is responsible for the higher photocurrent response. Also, the Ag NPs enable ultrafast photogenerated electron transfer by forming Schottky junctions. These two unique sensitized mechanisms were proposed for the first time in PEC sensing. Moreover, a one-step simple electrode modification strategy avoids tedious layer-by-layer assembly and rinsing steps. These make the “signal-on” SHO-PEC biosensor with remarkable advantages of high sensitivity, good specificity, strong reliability, fast speed, easy operation, and low cost. This research provides a new initiative for the development of PEC sensing platforms with excellent comprehensive performance.
Semiconductor quantum dots (QDs) are a promising class of nanomaterials for developing new photoelectrodes and photoelectrochemistry systems for energy storage, transfer, and biosensing applications. These materials have unique electronic and photophysical properties and can be used as optical nanoprobes in displays, biosensors, imaging, optoelectronics, energy storage and energy harvesting. Researchers have recently been exploring the use of QDs in photoelectrochemical (PEC) sensors, which involve exciting a QD-interfaced photoactive material with a flashlight source and generating a photoelectrical current as an output signal. The simple surface properties of QDs also make them suitable for addressing issues related to sensitivity, miniaturization, and cost-effectiveness. This technology has the potential to replace current laboratory practices and equipment, such as spectrophotometers, used for testing sample absorption and emission. Semiconductor QD-based PEC sensors offer simple, fast, and easily miniaturized sensors for analyzing a variety of analytes. This review summarizes the various strategies for interfacing QD nanoarchitectures for PEC sensing, as well as their signal amplification. PEC sensing devices, particularly those used for the detection of disease biomarkers, biomolecules (glucose, dopamine), drugs, and various pathogens, have the potential to revolutionize the biomedical field. This review discusses the advantages of semiconductor QD-based PEC biosensors and their fabrication methods, with a focus on disease diagnostics and the detection of various biomolecules. Finally, the review provides prospects and considerations for QD-based photoelectrochemical sensor systems in terms of their sensitivity, speed, and portability for biomedical applications.
A novel photoelectrochemical glucose sensor was constructed based on three-dimensional (3D) porous GaN photoanode fabricated via wet etching of as-grown GaN epitaxial wafer. The increased photocurrents indicated glucose can be photooxidized by 3D porous GaN in both neutral and alkaline electrolytes. In neutral electrolyte, the detection range and sensitivity were 100 µM to 3.6 mM and 40.14 µA mM⁻¹ cm⁻², respectively. In alkaline electrolyte, the detection range was 1 µM to 6.66 mM, and the sensitivities were 631.9 µA mM⁻¹ cm⁻² in the range of 1–161 µM and 60.03 µA mM⁻¹ cm⁻² in the range of 161 µM to 6.66 mM. Moreover, 3D porous GaN exhibited favorable reproducibility, good selectivity and satisfied stability toward glucose detection. In addition, this sensor can detect glucose in human serum samples, demonstrating the good practicability of 3D porous GaN.
Exosome is an emerging tumor marker, whose concentration level can reflect the occurrence and development of tumors. The development of rapid and sensitive exosome detection platform is of great significance for early warning of cancer occurrence. Here, a strategy for electrochemical detection of A549-cell-derived exosomes was established based on DNA/ferrocene-modified single-walled carbon nanotube complex (DNA/SWCNT-Fc). DNA/SWCNT-Fc complexes function as a signal amplification platform to promote electron transfer between electrochemical signal molecules and electrodes, thereby improving sensitivity. At the same time, the exosomes can be attached to DNA/SWCNT-Fc nanocomposites via the established PO4³⁻-Ti⁴⁺-PO4³⁻ method. Moreover, the application of EGFR antibody, which can specifically capture A549 exosomes, could improve the accuracy of this sensing system. Under optimal experimental conditions, the biosensor showed good linear relationship between the peak current and the logarithm of exosomes concentration from 4.66 × 10⁶ to 9.32 × 10⁹ exosomes/mL with a detection limit of 9.38 × 10⁴ exosomes/mL. Furthermore, this strategy provides high selectivity for exosomes of different cancer cells, which can be applied to the detection of exosomes in serum samples. Thus, owing to its advantages of high sensitivity and good selectivity, this method provides a diversified platform for exosomes identification and has great potential in early diagnosis and biomedical applications.
Cancer is a leading cause of death globally and early diagnosis is of paramount importance for identifying appropriate treatment pathways to improve cancer patient survival. However, conventional methods for cancer detection such as biopsy, CT scan, magnetic resonance imaging, endoscopy, X-ray and ultrasound are limited and not efficient for early cancer detection. Advancements in molecular technology have enabled the identification of various cancer biomarkers for diagnosis and prognosis of the deadly disease. The detection of these biomarkers can be done by biosensors. Biosensors are less time consuming compared to conventional methods and has the potential to detect cancer at an earlier stage. Compared to conventional biosensors, photoelectrochemical (PEC) biosensors have improved selectivity and sensitivity and is a suitable tool for detecting cancer agents. Recently, 2D carbon materials have gained interest as a PEC sensing platform due to their high surface area and ease of surface modifications for improved electrical transfer and attachment of biorecognition elements. This review will focus on the development of 2D carbon nanomaterials as electrode platform in PEC biosensors for the detection of cancer biomarkers. The working principles, biorecognition strategies and key parameters that influence the performance of the biosensors will be critically discussed. In addition, the potential application of PEC biosensor in clinical settings will also be explored, providing insights into the future perspective and challenges of exploiting PEC biosensors for cancer diagnosis.
Photoelectrochemical (PEC) biosensing as a promising and largely developing technique has been widely applied in biological analysis in recent years because of its low background signal and high sensitivity. By utilizing suitable PEC active materials to establish a photoelectric (PE) conversion system, selective and sensitive measurements can be achieved with the help of specific biological recognition elements. PEC biosensors rely on the change of photocurrent that depends on the electron transfer process of nanomaterials. Therefore, the electron manipulation of PEC active nanomaterials is crucial for PEC sensing. In this review, from the perspective of the electron transfer manipulation of PEC active nanomaterials, we summarize the principle of PEC biosensors in three parts, i.e., generation of excited electrons in PEC active materials, introduction of specific materials for the formation of new electron transfer pathways, and separation of excited electrons in semiconductors. For each part, typical PEC biosensors are displayed and compared to reveal the superiority of different principles. In addition, current challenges of PEC biosensors are discussed, and some insight is given into the development of PEC biosensors in the future.
A signaling strategy can directly determine the analytical performance and application scope of photoelectrochemical (PEC) immunoassays, so it is of great significance to develop an effective signaling strategy. The electro-Fenton reaction has been extensively used to degrade organic pollutants, but it has not been applied to PEC immunoassays. Herein, we report a novel signaling strategy for a PEC immunoassay based on electro-Fenton degradation of liposomes (Lip) on a photoelectrode. Lip vesicles are coated on Au@TiO2 core-shell photoactive material, which can prevent ascorbic acid (AA) from scavenging photogenerated holes. In the presence of a target, the immunomagnetic bead labels are converted to Fe3+ for electro-Fenton reaction, and hydroxyl radicals generated by the electro-Fenton reaction can degrade the Lip vesicles on the photoelectrode. Because of the degradation of Lip vesicles, photogenerated holes can be scavenged more effectively by AA, leading to an increase in photocurrent. Based on the electro-Fenton-regulated interface electron transfer, the sensitive "signal on" PEC immunoassay of a carcinoembryonic antigen is achieved, which features a dynamic range from 0.05 to 5 × 104 pg mL-1 and a detection limit of 0.01 pg mL-1. Our work provides a novel and efficient PEC immunoassay platform by introducing the electro-Fenton reaction into PEC analysis.
Exploiting innovative strategies with signal amplification in photoelectrochemical (PEC) biosensing systems to realize sensitive screening of low-abundance proteins has become one of the mainstream research orientations. Herein we reported a new strategy to amplify photocurrent signal employing a photocatalyst-electrolyte effect in alkaline media for the sensitive monitoring of prostate-specific antigen (PSA) using snowflake-liked [email protected]2S4 heterojunction as photosensitizer. In this strategy, both the band-edge position and surface redox reaction process were subtly altered by modulating the alkalinity of electrolyte. The hydroxyl anions (OH⁻) from NaOH could be oxidized to hydroxyl radicals (·OH) by the holes in [email protected]2S4, thus accelerating the scavenging of holes and promoting the photocurrent. Based on the above-mentioned mechanism, a sensitive split-type glucose oxidase-mediated PEC immunosensor for PSA detection was fabricated. Upon target PSA introduction, the glucose acid was generated through the sandwich-type immunoreaction to affect the alkalinity of PEC detection environment, thereby suppressing the photocurrent intensity. The [email protected]2S4-based PEC immunosensor exhibited satisfactory photocurrent responses with a good linear range of 0.04–40 ng mL⁻¹ at a limit of detection of 14 pg mL⁻¹. Significantly, this research not only introduces an effective strategy to detect PSA with good sensitivity and specificity, but also provides a new insight to amplify the signal by regulating the electrolyte.
Herein, based on CRISPR/Cas12a and catalytic hairpin assembly (CHA) non-enzyme amplification technology, a general photoelectrochemical (PEC) biosensor with high sensitivity and specificity is constructed using Bi/g-C3N4 nanohybrids as photoelectric composite electrode for the detection of miRNA-122. Notably, the single-strand DNA labelled with the sensitizer methylene blue (MB) was combined with the electrode to secondary improved the photocurrent response and effectively reduced the detection background. The miRNA-122 was specifically recognized by the CHA process, and then amplified into a rich signal output, which effectively improved the detection sensitivity. The target DNA complex generated by CHA cycle on the electrode surface hybridized with Cas12a-crRNA duplex to formed the Cas12a-crRNA-target DNA ternary complex, which activated their trans-cleavage ability and repelled MB to leave the electrode surface. The PEC signal was significantly reduced, achieving accurate detection of the miRNA-122. Under the action of multiple amplification mechanisms, the sensor showed prominent sensitivity and selectivity, the universal CRISPR/Cas12a cutting characteristics further expanded its analysis potential and simplified the operation difficulty, which can expand the application in biomedical detection and clinical diagnosis, showing great potential in efficient nucleic acid detection and in vitro diagnosis.
As an important heptapeptide toxin, microcystine-LR (MC-LR) has attracted extensive attention because of its great harm to animals, plants and plankton in water. Therefore, an ultrasensitive photoelectrochemical aptasensor based on ZnIn2S4/CdSe heterojunction was disigned to monitor MC-LR. In this strategy, the ZnIn2S4/CdSe heterojunction with matching energy levels was used as the substrate of the aptasensor. By reason of the effective separation of electrons and holes, the heterojunction exhibited wide light absorption region and increased light utilization rate, resulting in a higher electrical signal. The specific recognition of MC-LR depend on the precise binding with aptamer, which modified on the electrode through base complementary pairing. In the presence of MC-LR, MC-LR was specific recognized by MC-LR aptamer, the photocurrent signal amplifier Bi2S3 was released from the aptasensor electrode, leading to a decreased photocurrent. The designed photoelectrochemical aptasensor showed an ultrasensitive detection for MC-LR with a wide response range from 10⁻¹ to 10⁻⁸ µM, and lower detection limit of 0.55×10⁻⁸ µM (3σ/S).
Based on the necessity and urgency of cardiac troponin I (cTnI) detection for the diagnosis of myocardial infarction, a novel unlabeled photoelectrochemical (PEC) immunosensor has been developed to detect cTnI rapidly and sensitively. Silicon nanowire arrays (SiNWs) were prepared via metal-assisted chemical etching. To improve the stability and sensitivity towards cTnI sensing, the surface of silicon nanowire arrays were coated with polydopamine by an in situ growth method. PDA was uniformly modified on the nanowire surface to provide a reliable active site for antibody binding. The linear dynamic range of the cTnI detection method was 0.005-10 ng mL-1, and the detection limit was 1.47 pg mL-1. The designed PEC immunosensor exhibited good sensitivity, selectivity, stability and reproducibility. The electrode enabled label-free detection and provided a new route to realize point-of-care testing of cTnI.
Hybridization chain reaction (HCR), a one-dimensional DNA self-assembly process, is considered to be an enzyme-free isothermal amplification method. It shows great prospects and provides a wide range of applications for the construction of biosensors. In recent years, photoelectrochemistry (PEC) biosensor has attracted extensive attention as a new bioanalysis technology. In this work, we addressed the progress in the development of PEC biosensors in combination with the HCR-based signal amplification © 2022 The Authors. Published by ESG (www.electrochemsci.org). This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution license (http://creativecommons.org/licenses/by/4.0/)
Signal amplification strategies are of great interest in photoelectrochemical (PEC) sensing research. Herein, we explored a novel approach whereby hole transfer was accelerated from the photosensitive material Blue-TiO2 (B-TiO2) to the hole mediator N-hydroxyphthalimide (NHPI). Simultaneously, the introduction of the organic molecule NHPI can promote the efficiency of visible light absorption and expand the absorption range of B-TiO2. Under visible light irradiation, the photocurrent value of NHPI/B-TiO2 is 2.7-fold larger than that of B-TiO2, which can be ascribed to the acceleration of hole transfer by NHPI. More specifically, NHPI acts as a hole mediator, which effectively transfers photo-generated holes from the valence band (VB) of B-TiO2 to NHPI. NHPI can be oxidized to phthalimide-N-oxyl radical (PINO*), thereby causing inhibition of photo-generated carrier recombination and enhancement of the photocurrent. Furthermore, a PEC aptasensor for the sensitive detection of diazinon (DIA) was constructed by combining specific aptamers on an NHPI/B-TiO2 nanocomposite surface. The oxidation product of NHPI, PINO*, oxidizes the DIA captured by the aptamer. Under optimized experimental conditions, the linear range for DIA detection was 0.1-1000 nM, and the detection limit of the NHPI/B-TiO2 nanocomposite aptamer sensing was 0.03 nM (S/N=3). Therefore, this proposed method involving the hole mediator can be used as a new strategy to improve the performance of PEC.
Using an In2O3/WO3 type-II heterojunction modified fluorine-doped tin oxide (FTO) electrode as the photoanode and CdS quantum dots (QDs)-polydopamine nanospheres (PDA NSs) as the secondary antibody (Ab2) label, the photoelectrochemistry (PEC) sandwich immunosensing of the lung cancer marker CYFRA21-1 was studied. WO3 nanoplates were prepared by a hydrothermal method, In2O3 nanoporous spheres were prepared by a hydrothermal method followed by calcination, and the In2O3/WO3 type-II heterojunction with high PEC activity was prepared by ultrasonic mixing and cast-coating. PDA NSs with a high surface area can be loaded with abundant Ab2 molecules and many CdS QDs with an energy level well matched with the heterojunction, so the photocurrent signal can be amplified by the formation of a sandwich immunostructure. Through the simulation experiments of photoelectrode-modified chitosan films of varying thickness, the effective transport distance of photogenerated charges is preliminarily discussed. Under the optimized conditions, the photocurrent was linear with the common logarithm of CYFRA21-1 concentration from 100 fg mL-1 to 50 ng mL-1, with a limit of detection of 56 fg mL-1 (S/N = 3). The immunoassay of CYFRA21-1 in human serum samples gave satisfactory recovery results.
As a noninvasive substitute for traditional tissue biopsy, liquid biopsy has emerged as a novel method for the early diagnosis of malignant tumors. In the past decade, low-cost biosensors have been widely studied, and compared to other methods, they have exhibited superior performance in bioanalysis, including liquid biopsies. With the advanced generation of optical and electrochemical biosensors, photoelectrochemical (PEC) biosensors coupled with nanosciences (referred to as PEC nanosensors) have attracted much attention in recent years as they have reached an even higher sensitivity. In this review, the working principle, detection strategy and photoactive nanomaterials of PEC nanosensors were summarized, recent applications of PEC nanosensors for diagnosing different tumor biomolecules in liquid samples were reviewed, and the design process for each type of PEC nanosensor were especially considered. Finally, some perspectives on developing PEC nanosensors were provided. This review provides systematic retrospective analysis and insights for developing PEC nanosensors in cancer liquid biopsy.
Development of novel photoactive materials is of great significance for improving the analytical performance of photoelectrochemical (PEC) biosensors. Herein, sensitive PEC biosensor was developed based on organic PM6:Y6 p-n heterojunction as photoactive matrix for circulating tumor cells (CTCs) detection. Y6, as organic acceptor that combines with the organic donor PM6 forms p-n heterojunction promoted separation of photo-generated charges with high charge transfer efficiency, resulting in the enhancement of photocurrent intensity. The detection of CTCs was achieved through the traditional “sandwich” protocol. Magnetic nanobeads (MNs) decorated with anti-epithelial cell attachment molecule antibody (anti-EpCAM) were used for capturing and separate CTCs, while the Au-aptamer probe and silver staining reaction were designed for dual signal amplification. The localized surface plasmon resonance (LSPR) of gold nanoparticles (Au NPs), and silver nanoparticles (Ag NPs) that generated by silver staining reaction improved photocurrent response of PEC sensor. This PEC biosensor was applied to detect MCF-7 and displayed an ultra-low detection limit of 9 cell mL- 1 and linear range from 10 to 10000 cell mL⁻¹. This work explored a path for the application of organic semiconductors as photoactive materials in PEC sensing, which may find broad applications for detecting varied analytes.
Small-molecule photosensitizers have great application prospects in photoelectrochemical (PEC) sensing due to their defined composition, diversified structure, and adjustable photophysical properties. Herein, we propose a new strategy for PEC analysis based on the target-induced in situ formation of the organic photosensitizer. Taking thiophenol (PhSH) as a model analyte, we designed and synthesized a 2,4-dinitrophenyl (DNP)-caged coumarin precursor (Dye-PhSH), which was then covalently coupled onto the TiO2 nanoarray substrate to obtain the working photoanode. Due to the intramolecular photoinduced electron transfer process, Dye-PhSH has only a very weak photoelectric response. Upon reacting with the target, Dye-PhSH undergoes a tandem reaction of the detachment of the DNP moiety and the intramolecular cyclization process, which leads to a coumarin dye with a pronounced photoelectric effect, thus achieving a highly selective turn-on PEC response to PhSH. For the first time, this study was to construct a PEC sensor by exploiting specific organic reactions for the in situ generation of small molecule-based photoactive material. It can be anticipated that the proposed strategy will expand the paradigm of PEC sensing and holds great potential for detecting various other analytes.
There is an intensive search for heterogeneous single atom catalysts (SACs) of high activity, efficiency, durability, and selectivity for a wide variety of electrocatalytic conversion and chemical reactions, such as the hydrogen evolution reaction (HER), oxygen evolution/reduction reaction (OER and ORR), CO2 reduction reaction (CO2 RR), and nitrogen reduction reaction (NRR). With the downsizing from nanoparticles and clusters to single atoms, there are steady changes in the bond and coordination environment for each and every atom involved. Indeed, the single atoms in these electrocatalysts are not “singles”; they are “married” to the supporting surfaces, and their performance is controlled by the bonding and coordination with the substrate surfaces. Herein, an overview is presented on the brief history leading to the rapid development of SACs and their current status, by focusing on their synthesis, control of composition, strategies to realize single atoms with the desired bonds and coordination, and targeted performance in selected reactions. Their applications in the selected spectrum of energy conversion and chemical reactions are discussed, in relation to their structures at varying length scales down to the atomic level. A particular emphasis is placed on on‐going research activities, together with the future perspectives and particular challenges for SACs.
Electrocatalytic nitrogen reduction reaction (NRR) has much prospect for substituting the energy-consuming Haber-Bosch process. Nevertheless, its sluggish reaction kinetics and the competing hydrogen evolution reaction always result in limited ammonia yield and low Faradaic efficiency (FE). In this work, the Fe-decorated porphyrinic metal-organic framework (MOF) is employed as a precursor to construct single-atom Fe implanted nitrogen-doped carbon catalysts (Fe1-N-C) through a mixed ligand strategy. Benefiting from the highly dispersed single-atom Fe sites, hierarchically porous structure and good conductivity, Fe1-N-C shows a FE of 4.51% and ammonia yield rate of 1.56×10-11 mol cm-2 s-1 at -0.05 V versus reversible hydrogen electrode, superior to those of Co1-N-C and Ni1-N-C. Theoretical calculations reveal that Fe1-N-C shows the lowest energy barrier of the rate-determining step during NRR process, accordant to its highest activity obtained in experiments. This work reveals the unique potential of single-atom catalysts for electrochemical NRR and provides in-depth insights into the catalytic mechanism of NRR.
A new organic-inorganic heterostructure was prepared by hydrothermally depositing poly (3,4-dioxoethylthiophene) (PEDOT) on TiO2 nanowire arrays (TiONWs) to construct a biosensor that can simultaneously function both as photoelectrochemical (PEC) and electrochemical (EC) sensor to detect lactate. In both cases, the PEDOT-TiONWs heterostructure not only acted as an immobilization platform for lactate dehydrogenase (LDH) and coenzyme NAD⁺, but also generated current signals, which were further amplified by the cyclic catalytic mechanism. Specifically, LDH catalytically converted lactate to pyruvate, meanwhile NAD⁺ was transformed to NADH. For PEC sensing, the photo-generated holes from PEDOT-TiONWs could oxidize NADH back to NAD⁺, fulfilling a catalytic cycle. Herein, PEDOT significantly promoted the separation of electron-hole pairs and enhanced PEC signals due to its well-matched energy levels with TiONWs, high conductivity and strong visible light absorption. A dynamic range of 0.5–300 μM was observed between the PEC signals and lactate concentration, based on which a sensitivity of 0.1386 ± 0.0053 μA μM⁻¹ and a detection limit of 0.08 ± 0.0032 μM were estimated. For EC sensing, PEDOT-TiONWs could directly oxidize NADH to NAD⁺ at ∼0.54 V to realize the cyclic amplification due to the high conductivity and strong electrocatalytic capability of the heterostructure. The EC biosensor displayed a similar performance upon PEC mode of operation, except the relatively poor selectivity due to the possible oxidation of the interferences at the potentials over 0.54 V.
As a newly developed and powerful analytical method, photoelectrochemical (PEC) biosensors open up new opportunities to provide wide applications in early diagnosis of diseases, environmental monitoring and food safety detection. The properties of diverse photoactive materials are one of the essential factors, which can greatly impact the PEC performance. The continuous development of nanotechnology has injected new vitality into the field of PEC biosensors. In many studies, much efforts on PEC sensing with semiconductor materials are highlighted. Thus, we propose a systematical introduction of recent progress in nanostructures-based PEC biosensors to exploit more promising materials and advanced PEC technologies. This review briefly evaluates the several advanced photoactive nanomaterials in PEC field with an emphasis on charge separation and transfer mechanism over the past few years. In addition, we introduce the application and research progress of PEC sensor from the perspective of basic principle, and give a brief overview of the main advances in versatile sensing pattern of nanostructures-based PEC platforms. This last section covers the aspects of future prospects and challenges in the nanostructures-based PEC analysis field.
Mycotoxins, highly toxic secondary metabolites of fungus, have brought considerable threats to human health. It is of great significance to develop low-cost, rapid and efficient analytical methods for monitoring mycotoxins in foodstuffs. Photoelectrochemical (PEC) biosensors have been promising tools for mycotoxin detection thanks to their superior properties. Photoactive materials play important roles in the biosensing systems as transducer converting chemical information into detectable PEC signal. Signal strategies based on specific recognition elements also affects a lot on the analytical performance of PEC biosensors. This paper provides a comprehensive review on photoactive materials and signal strategies used in the PEC biosensors for mycotoxin monitoring. The future prospects in this field are also discussed.
A signal-on photoelectrochemical (PEC) biosensor was successfully established for the sensitive monitoring of carcinoembryonic antigen (CEA) by using copper indium disulfide-sensitized graphitic-like carbon nitride (g-C3N4/CuInS2) as the photosensitive material and cobalt oxyhydroxide (CoOOH) as the light-blocking material, coupling target-triggered hybridization chain reaction (HCR) with hydrolysate-induced dissolution/etching of CoOOH nanosheets. Initially, a sandwiched reaction occurred between capture aptamer-conjugated magnetic bead and trigger aptamer in the presence of CEA. Then, the carried trigger aptamer initiated HCR between two hairpin sequences to produce long double-helix strand for capturing alkaline phosphatase. The generated ascorbic acid reduced/etched CoOOH nanosheets into divalent cobalt ions, which decreased the amount and thickness of CoOOH and exposed the underlying g-C3N4/CuInS2, thus leading to a distinct increase in the photocurrent. Under optimum conditions, PEC sensor showed high sensitivity toward CEA with a dynamic range of 0.02−40 ng mL⁻¹ and a detection limit of 5.2 pg mL⁻¹. Also, it possessed favorable selectivity, high stability as well as good precision. The accuracy of PEC approach was well consistent with commercial CEA ELISA kit. These exceptional analytical performances of PEC biosensor indicated that it might have a broad application prospect in the diagnosis of CEA.
This work reports a ZIF-8 (ZIF: Zeolitic Imidazolate Framework)-assisted NaYF4:Yb,[email protected] upconverter for the photoelectrochemical (PEC) biosensing of carcinoembryonic antigen (CEA) under near-infrared (NIR) irradiation on a homemade 3D-printing device with DNA walker-based amplification strategy. The composite photosensitive material NaYF4:Yb,[email protected], as converter to transfer NIR import to photocurrent output, was driven from annealed NaYF4:Yb,[email protected] Yb3+ and Tm3+-codoped NaYF4 (NaYF4:Yb,Tm) converted NIR excitation into UV emission, matching with the absorption of ZnO for in-situ excitation to generate the photocurrent. Upon target CEA introduction, the swing arm of DNA walker including the sequence of CEA aptamer carried out the sandwiched bioassembly with CEA capture aptamer on the G-rich anchorage DNA tracks-functionalized magnetic beads. Thereafter, DNA walker was triggered, and the swing arm DNA was captured by the G-rich anchorage DNA according to partly complementary pairing and Exonuclease III (Exo III) consumed anchorage DNA by a burnt-bridge mechanism to go into the next cycle. The released guanine (G) bases from DNA walker enhanced the photocurrent response on a miniature homemade 3D-printing device consisting of the detection cell, dark box and light platform. Under optimal conditions, NaYF4:Yb,[email protected] NIR light-driven PEC biosensor presented high sensitivity and selectivity for CEA sensing with a detection limit of 0.032 ng mL-1. Importantly, our strategy provides a new horizon for the development of NIR-based PEC biosensors in the aspect of developing MOF-derived photoelectric materials, flexible design of 3D-printing device and effective signal amplification mode.
Photoelectrochemical sensing is an attractive tool for rapid and accurate monitor of chemical and biochemical mole-cules. Compared with conventional analysis techniques, photoelectrochemical sensing exhibits unique technique superiority and has become a hot topic in material chemis-try and analytical chemistry. This review provides an over-view of the important advances in the construction and application of photoelectrochemical sensing in recent year. In the first segment, we briefly introduce the general princi-ple and technical characteristic of photoelectrochemical sensing. In the subsequent sections, we primarily devote to elaborating the typical strategies of design and engineering photoactive materials for improve the light excitation as well as charge separation/transfer to modulate the perfor-mance of photoelectrochemical sensing system. Addition-ally, the current research status of photoelectrochemical sensing with a particular emphasis on the innovative sens-ing devices and detection modes for achieving specific sensing functions is describes in detail with the illustrative examples. Finally, the critical challenges on the journey to achieve real-life applications of photoelectrochemical sens-ing and the viable solutions for solving these problems as well as the future research perspectives are discussed.
A ratiometric photoelectrochemical (PEC) sensing strategy was proposed for monitoring of carcinoembryonic antigen (CEA) based on a homemade 3D printing device with dual-working photoelectrodes (PE1 and PE2), coupling λ-exonuclease (λ-Exo)-assisted recycling amplification with CdS quantum dots. Gold nanoparticles-functionalized ZnO nanorods were utilized as PEC substrate for generating initial photocurrent and immobilizing DNA probe. Upon incu-bation of target with DNA trigger/CEA aptamer-modified magnetic bead (tri/apt-MB), DNA trigger dissociated from magnetic bead and then hybridized with capture probe (cp) on PE1 or opened hairpin probe (hp) on PE2 to form dou-ble-stranded DNA (dsDNA). The exonuclease could recognize and cleave two newly generated dsDNA, leading to the release of trigger. The free trigger strand continued to hybridize with the remaining cp/hp, which were cleaved by λ-Exo, and then trigger was released again and restarted next recycle with the λ-Exo. After digestion of λ-Exo, the num-ber of capture probes on PE1 was reduced, and many short DNA fragments were produced on PE2, thereby resulting in the decreasing CdS QDs on PE1 and the increasing CdS QDs on PE2. As a result, it was observed that the ratio value of photocurrents (PE1/PE2) significantly decreased with the increasing CEA. Under optimum conditions, the sensing method showed a good linear relationship toward CEA within the dynamic range of 0.02-10 ng mL-1 and a detection limit of 6.0 pg mL-1. Moreover, the ratiometric PEC sensor exhibited good reproducibility, satisfying stability, and re-markable anti-interference performance, which suggests its promising application prospect to detect target CEA.
This work designed a MgIn2S4-TiONA heterojunction by growing MgIn2S4 nanoplates on TiO2 nanowire array (TiONA) for preparation of visible light photoelectrochemical (PEC) sensing platform. The heterojunction exhibited strong absorption of visible light, large surface area and high loading of biomolecules, leading to high sensing sensitivity. Using adenosine triphosphate (ATP), a marker of cell vitality, as the target model, a PEC sandwich aptasensor was constructed by immobilizing capture DNA1 on MgIn2S4 surface. In the presence of ATP and signal DNA2 with terminal ferrocene as the electron donor, a sandwiched DNA1-ATP-DNA2 complex could be formed on the PEC aptasensor. The aptasensor showed excellent performance with a wide linear range from 50 fM to 100 nM and a detection limit of 20 fM. The sensing performance including specificity, reproducibility, stability and practical use were also evaluated, showing promising application of the MgIn2S4-TiONA heterojunction in PEC biosensing.
Promoting the efficient full utilization of photogenerated electrons and holes for dual-function photocatalytic pollutants removal has become a research hot spot. Herein, a well-designed Z-Scheme Co 3 O 4 /Ag/Bi 2 WO 6 nanocomposite was fabricated through a multi-step synthesis and applied for removing heavy metal ions Cr(VI) and antibiotic tetracycline hydrochloride (TCH) simultaneously under visible light irradiation for the first time. Compared to the half-reactions, the photocatalytic efficiency of Co 3 O 4 /Ag/Bi 2 WO 6 in removal of Cr(VI)-TCH coexistence system was found to be 6.86(Cr(VI)) and 2.58(TCH) times higher than that in its single system due to synergistic effects of photocatalytic reduction and oxidation with better utilization of electrons and holes. Meanwhile, The photocatalytic performance of Co 3 O 4 /Ag/Bi 2 WO 6 in simultaneous degradation of Cr(VI) and TCH is about 7.89 and 5.65 times higher than that of pure Bi 2 WO 6 , respectively. And ternary Co 3 O 4 /Ag/Bi 2 WO 6 photocatalyst exhibited much better photocatalytic activity compared with single Bi 2 WO 6 , Ag/Bi 2 WO 6 and Co 3 O 4 /Bi 2 WO 6 heterojunctions owing to the wide spectral response, more efficient photogenerated charge separation and utilization and strong redox capacity. Besides, the Z-Scheme photocatalytic enhanced mechanism of Co 3 O 4 /Ag/Bi 2 WO 6 heterojunction was proved based on the photoluminescence (PL), photoelectrochemical and electron spin resonance (ESR) measurements, band structure characterizations and corresponding theoretical analyses.
Oxygen defect-engineered is an important strategy to improve the photoelectric activity of materials. Herein, a facile one-pot solvothermal method was utilized to synthesize visible light-responsive photoactive Bi 2 MoO 6 nanoparticles anchored boron and nitrogen co-doped graphene (BNG) nanosheets nanocomposites with oxygen vacancy. The incorporation of BNG nanosheets increased the oxygen vacancies amounts on Bi 2 MoO 6 remarkably, and the presences of oxygen vacancies can be beneficial to broaden the absorption range. The absorption edge of Bi 2 MoO 6 /BNG was widened from 500 nm to 550 nm compared to Bi 2 MoO 6 , and the charge transfer was accelerated to improve the photoactive of Bi 2 MoO 6 /BNG. Under visible light illumination, the photoelectrochemical (PEC) response of the as-prepared Bi 2 MoO 6 /BNG was 11.6-fold, 6.7-fold, 3.1-fold and 2.4-fold higher than that of pristine Bi 2 MoO 6 , Bi 2 MoO 6 /graphene, Bi 2 MoO 6 /nitrogen doped graphene and Bi 2 MoO 6 /boron doped graphene. Using Bi 2 MoO 6 /BNG nanocomposites with the superior PEC performance as photoactive materials in combination with specifically recognized lincomycin (LIN) aptamer, a highly efficient PEC aptasensor was successfully constructed for sensitive analysis of LIN. Under optimal conditions, the proposed PEC aptasensor exhibited excellent analytical performance for LIN with a wide linear response of 1 × 10 ⁻¹¹ to 1 × 10 ⁻⁶ mol L ⁻¹ along with a low detection limit of 3.7 × 10 ⁻¹² mol L ⁻¹ (defined as S/N = 3). The as-prepared Bi 2 MoO 6 /BNG nanocomposites exhibit excellent visible light response and PEC performance, indicating its potential applications in PEC biosensor.
Saline-alkali soil is a major environmental constraint impairing plant growth and crop productivity. In this study, we identified a Ca2+ sensor/kinase/plasma membrane (PM) H+-ATPase module as a central component conferring alkali tolerance in Arabidopsis (Arabidopsis thaliana). We report that the SCaBP3 (SOS3-LIKE CALCIUM BINDING PROTEIN3)/CBL7 (CALCINEURIN B-LIKE7) loss-of-function plants exhibit enhanced stress tolerance associated with increased PM H+-ATPase activity and provide fundamental mechanistic insights into the regulation of PM H+-ATPase activity. Consistent with the genetic evidence, interaction analyses, in vivo reconstitution experiments, and determination of H+-ATPase activity indicate that interaction of the Ca2+ sensor SCaBP3 with the C-terminal Region I domain of the PM H+-ATPase AHA2 (Arabidopsis thaliana PLASMA MEMBRANE PROTON ATPASE2) facilitates the intramolecular interaction of the AHA2 C terminus with the Central loop region of the PM H+-ATPase to promote autoinhibition of H+-ATPase activity. Concurrently, direct interaction of SCaPB3 with the kinase PKS5 (PROTEIN KINASE SOS2-LIKE5) stabilizes the kinase-ATPase interaction and thereby fosters the inhibitory phosphorylation of AHA2 by PKS5. Consistently, yeast reconstitution experiments and genetic analysis indicate that SCaBP3 provides a bifurcated pathway for coordinating intramolecular and intermolecular inhibition of PM H+-ATPase. We propose that alkaline stress-triggered Ca2+ signals induce SCaBP3 dissociation from AHA2 to enhance PM H+-ATPase activity. This work illustrates a versatile signaling module that enables the stress-responsive adjustment of plasma membrane proton fluxes.
In this work, a novel photoelectrochemical (PEC) aptasensor was developed for the sensitive detection of aflatoxin B1 (AFB1) based on a resonance energy transfer strategy between Ce-TiO2@MoSe2 heterostructure and Au nanoparticles (AuNPs). Ce-TiO2@MoSe2 composite was obtained by growing MoSe2 nanosheets on a TiO2 nanocube doped by Ce element with a facile hydrothermal method. The composite effectively extended the absorption of TiO2 to the visible region and avoided the self-aggregation of MoSe2 nanosheets, leading to the excellent photocurrent response under visible light excitation. The PEC aptasensor was then fabricated by immobilizing Ce-TiO2@MoSe2 composite on an ITO electrode, followed by the modification of aminated AFB1 aptamer. An AuNPs-labeled DNA sequence was subsequently hybridized with the aptamer to fabricate a sandwich structure, which was destroyed after the introduction of AFB1, decreasing the amount of energy acceptor (AuNPs) at the electrode surface. Accordingly, the photocurrent was increased with the increase of AFB1 concentration. Under the optimal conditions, the PEC aptasensor showed a wide linear range of 0.03–200 ng mL-1 and a low detection limit of 0.01 ng mL-1 for AFB1 determination.
A key characteristic of chloroplast gene expression is the predominance of posttranscriptional control via numerous nucleus-encoded RNA binding factors. Here, we explored the essential roles of the S1-domain-containing protein photosynthetic electron transfer B (petB)/ petD Stabilizing Factor (BSF) in the stabilization and translation of chloroplast mRNAs. BSF binds to the intergenic region of petB-petD, thereby stabilizing 3' processed petB transcripts and stimulating petD translation. BSF also binds to the 5' untranslated region of petA and activates its translation. BSF displayed nucleic-acid-melting activity in vitro, and its absence induces structural changes to target RNAs in vivo, suggesting that BSF functions as an RNA chaperone to remodel RNA structure. BSF physically interacts with the pentatricopeptide repeat protein Chloroplast RNA Processing 1 (AtCRP1) and the ribosomal release factor-like protein Peptide chain Release Factor 3 (PrfB3), whose established RNA ligands overlap with those of BSF. In addition, PrfB3 stimulated the RNA binding ability of BSF in vitro. We propose that BSF and PrfB3 cooperatively reduce the formation of secondary RNA structures within target mRNAs and facilitate AtCRP1 binding. The translation activation function of BSF for petD is conserved in Arabidopsis (Arabidopsis thaliana) and maize (Zea mays), but that for petA operates specifically in Arabidopsis. Our study sheds light on the mechanisms by which RNA binding proteins cooperatively regulate mRNA stability and translation in chloroplasts.
An all-solid-state metal-mediated Z-scheme photoelectrochemical (PEC) immunoassay was designed for sensitive detection of prostate-specific antigen (PSA) by using WO 3 -Au-CdS nanocomposite as photoactive material and copper ion (Cu ²⁺ ) as an inhibitor. The Z-scheme PEC system comprising of CdS nanoparticle (photosystem I; PS I), WO 3 nanorod (photosystem II; PS II) and gold nanoparticle (Au NP; solid electron mediator) was reasonably established by a simple and green synthetic method. As an important part of Z-scheme system, the sandwiched gold nanoparticles between electron donor materials and hole provider materials could accelerate electron transfer from positive conduction band (CB) of WO 3 to negative valence band (VB) of CdS, thus resulting in high-efficient separation of the carriers. In the presence of target PSA, a sandwiched immunoreaction was executed between capture antibody-coated microplate and CuO nanoparticle-labeled detection antibody. Thereafter, CuO nano labels were dissolved into Cu ²⁺ ions under acidic condition to decrease the photocurrent of Z-scheme WO 3 -Au-CdS thanks to the formation of exciton trapping center of Cu x S (x = 1,2) on the surface. Under optimum conditions, Z-scheme PEC immunoassay exhibited good photocurrents toward target PSA within a linear range of 0.01–50 ng mL ⁻¹ at a limit of detection of 1.8 pg mL ⁻¹ . Moreover, the Z-scheme PEC immunoassay had high selectivity and accuracy. Importantly, this method provides a new horizon for detection of disease-related biomarkers with high sensitivity.
It is essential to develop a highly efficient detection platform for tetracycline (Tc). Herein, based on well-designed hierarchical MIL-68(In)-NH 2 /MWCNT/CdS composites as a highly efficient transducer, a label-free visible light driven photoelectrochemical (PEC) aptasensor was systematically fabricated. Characterization results indicate that the forming of MIL-68(In)-NH 2 /CdS heterojunction remarkable facilitated the transfer and inhibited the recombination of charge carriers. Moreover, the transfer properties of multiwalled carbon nanotubes (MWCNTs) further improved the photoelectric conversion efficiency by adjusting electron transport routes. The aptamer as a biorecognition unit was grafted on the modified electrode by chemical bonding effect, and Tc molecules could be captured through the specific interaction of aptamer and Tc in solution. The concentration of Tc was detected by observing the fluctuation of photocurrent signals. Under optimized conditions, the proposed aptasensor showed the broad linear range from 0.1 nmol L ⁻¹ to 1 μmol L ⁻¹ with a low detection limit (LOD) of 0.015 nmol L ⁻¹ . Furthermore, the high sensitivity, excellent reproducibility and favorable stability of the PEC sensing platform indicated the potential applications for antibiotic residues detecting in environmental media.
A simple “signal-on” photoelectrochemical (PEC) aptasensor is constructed for Aflatoxin B1 (AFB1) detection based on electrochemically reduced graphene oxide/poly(5-formylindole)/Au (erGO/P5FIn/Au) nanocomposites. The nanocomposites are synthesized by simple electrochemical deposition method and show good photoelectrochemical performance. Poly(5-formylindole) (P5FIn) can generate electron-hole pairs under light irradiation, leading to the formation of robust cathode photocurrent. Au can be acted as signal amplifier due to the high conductivity. The erGO is used to immobilize AFB1 aptamer chain by π-π stacking interaction between the carbon six-membered ring in graphene and the C-N heterocyclic ring in nucleobases of ssDNA. After the insulating AFB1 aptamer chain is fixed to the electrode, the signal of PEC sensor is “OFF”. In the process of AFB1 detection, the aptamer chain detaches from the surface of erGO, which results in “ON” of the sensor signal. Based on this design, this constructed PEC aptasensor shows a high sensitivity for AFB1 with a wide linear detection range (LDR) from 0.01 ng mL ⁻¹ to 100 ng mL ⁻¹ . The limit of detection (LOD) is 0.002 ng mL ⁻¹ . This PEC sensor also exhibits good stability, selectivity, specificity, and satisfactory practical sample analysis ability. This work may provide a new promising PEC platform for AFB1 detection as well as some other small molecules analysis.
In this study, the novel visible light double Z-scheme photocatalysts (Ag 3 PO 4 /Bi 2 S 3 /Bi 2 O 3 ) were synthesized by the facile means. The crystal texture, chemical states, morphology and optical characteristics of prepared photocatalysts were investigated by XRD, FTIR, XPS, SEM, TEM, N 2 adsorption-desorption analysis, UV–vis DRS, and PL etc. techniques, respectively. Meanwhile, the band structures and the density of states of three single-phase semiconductor and Ag 3 PO 4 /Bi 2 S 3 /Bi 2 O 3 (ABB) composite had been calculated by Materials Studio program based on density functional theory. For assessing the photocatalytic performance of these samples, the visible light photodegradation of antibiotics sulfamethazine (SAZ) and cloxacillin (CLX) were performed. The effects of initial antibiotic concentration, reaction pH, supporting electrolyte and surfactant on photocatalytic performance were all investigated. The results indicated that the ABB-3 composite exhibited higher photocatalytic performance than other comparison samples. Furthermore, four cycle experiments confirmed the ABB-3 composite also exhibited satisfactory photostability. The scavenger tests and ESR data demonstrated that the active species h ⁺ , [rad] O 2⁻ , and [rad] OH worked together in the photocatalytic process, and the h ⁺ and [rad] O 2⁻ play a more important role than [rad] OH. All in all, the increased photocatalytic performance of ABB composite could owe to the photosensitization of Bi 2 S 3 and the double Z-scheme photocatalytic system. This study could inspire some new idea for building the novel and efficient heterogeneous photocatalysts and benefiting their practical application.
A novel p-type semiconductor-based cathodic “signal-on” photoelectrochemical (PEC) aptasensor was proposed for highly sensitive and selective detection of chloramphenicol (CAP). The photocathode was fabricated with hierarchical porous flower-like [email protected] composite synthesized via a one-pot solvothermal method using glucose as both green reductant and carbon precursor. Due to the surface plasmon resonance (SPR) effect of Bi and high-conductivity of carbon, the composite exhibited an enhanced cathodic photocurrent as compared with pure BiOI or Bi-BiOI. When CAP-binding aptamer was immobilized as recognition element on [email protected] modified electrode, a cathodic PEC aptasensor showing specific “signal-on” response to CAP was constructed. Some influencing factors such as coating amount of [email protected] suspension, applied bias potential, and aptamer concentration were studied. Under the optimum conditions, the cathodic photocurrent of the constructed PEC aptasensor increased linearly with CAP concentration from 2 to 250 nM, with a detection limit (3S/N) of 0.79 nΜ. The proposed sensor was successfully applied to the determination of CAP in pharmaceutical tablet, eye drop and lake water samples.
This work presented an innovative and rationally engineered palindromic molecular beacon (PMB)-based 'Z-scheme' photoelectrochemical (PEC) biosensing protocol for the selective screening of kanamycin (Kana) through DNA hybridization-induced conformational conversion. Interestingly, the ingenious-designed PMB integrated the multifunctional elements including recognition region, primer-like palindromic fragment and polymerization-nicking template. The co-sensitized structures consisted of CdS quantum dot-functionalized hairpin DNA2 (QD-HP2) and the region-selectively deposited gold nanoparticles onto {001} facets of BiOCl (BiOCl-Au). Compared with BiOCl-Au alone, the attachment of CdS QDs onto BiOCl-Au (i.e., BiOCl-Au-CdS QDs) exhibited evidently enhanced photocurrent intensity thanks to synergistic effect of 'Z-scheme' BiOCl-Au-CdS QDs. After incubation with target Kana, Kana-aptamer binding could induce the exposure of PMB region for hairpin DNA1 (HP1). The exposed palindromic tails hybridized with each other (like a molecular machine) to consume the substrates (dNTPs) and fuels (enzyme) for the releasing of numerous nick fragments (Nick). The as-generated nick fragments could specifically hybridize with the complementary region of QD-HP2, thus resulting in the decreasing photocurrent because of the increasing spatial distance for electron transfer between two-type photosensitizers. Under optimum conditions, PMB-based sensing system exhibited satisfying photocurrent responses toward target Kana within the working range from 50 to 5000 fM at a low detection limit of 29 fM. Impressively, the concept of palindromic fragment-mediated primer-free biosensing strategy offers a new avenue for advanced development of efficient and convenient bio-detection systems.
An ultrasensitive photoelectrochemical (PEC) aptasensor was designed for detection of chloramphenicol (CAP) based on graphene quantum dots-sensitized TiO2 nanotube arrays (GQDs/TiO2 NTs). The GQDs/TiO2 NTs nanohybrids were prepared by a coupling technique of linker molecule binding and electrophoretic deposition. It exhibited significantly enhanced visible-light photoelectrochemical activity, which was firstly employed as the photoactive material for fabrication of PEC aptasensor. As the recognition unit, the aptamers of CAP were immobilized on GQDs/TiO2 NTs photoelectrode via π–π stacking interaction between GQDs and the nucleobases of the aptamer. In this signal-on proposal, the aptasensor was used for the label-free analysis of CAP by monitoring the increase in photocurrent that resulted from the formation of aptamer-CAP bioaffinity complexes with ascorbic acid as an efficient electron donor for scavenging photogenerated holes. Under the optimized conditions, the aptasensor showed a wide linear range from 0.5 nM to 100 nM for CAP detection with a low detection limit of 57.9 pM (S/N = 3). With good selectivity and sensitivity, the PEC aptasensor was applied to the determination of CAP in spiked honey samples with satisfactory results, suggesting that the GQDs/TiO2 NTs photoelectrode has a promising application in constructing PEC sensor platform.
Lithium‐sulfur (Li‐S) battery based on sulfur cathodes is of great interest because of high capacity and abundant sulfur source. But the shuttling effect of polysulfides caused by charge‐discharge process results in low sulfur utilization and poor reversibility. Here, we demonstrate a good approach to improve the utility of sulfur and cycle life by synthesizing carbon nanofibers decorated with MoO2 nanoparticles (MoO2‐CNFs membrane), which plays a role of multiinterlayer inserting between the separator and the cathode for Li‐S battery. The S/MoO2‐CNFs/Li battery showed a discharge capacity of 6.93 mAh cm⁻² (1366 mAh g⁻¹) in the first cycle at a current density of 0.42 mA cm⁻² and 1006 mAh g⁻¹ over 150 cycles. Moreover, even at the highest current density (8.4 mA cm⁻²), the battery achieved 865 mAh g⁻¹. The stable electrochemical behaviors of the battery has achieved because of the mesoporous and interconnecting structure of MoO2‐CNFs, proving high effect for ion transfer and electron conductive. Furthermore, this MoO2‐CNFs interlayer could trap the polysulfides through strong polar surface interaction and increases the utilization of sulfur by confining the redox reaction to the cathode.
A near-infrared light (NIRL)-activated ratiometric photoelectrochemical (PEC) aptasensor was fabricated for detection of carcinoembryonic antigen (CEA) coupling with upconversion nanoparticles (UCNPs)-semiconductor nanocrystals-based spatial-resolved technique on a homemade 3D printing device in which a self-regulating integrated electrode was designed for dual signal readout. The as-prepared NaYF4:Yb, Er UCNPs@CdTe nanocrystals were initially assembled on two adja-cent photoelectrodes, then CEA aptamer 1 (A1) and capture DNA (CA) were modified onto two working photoelectrodes (WP1 and WP2) through covalent binding, respectively, and then gold nanoparticle-labeled CEA aptamer 2 (Au NP-A2) were immobilized on the surface of functional WP2 for the formation of double-stranded DNA. Upon target CEA introduction, the various concentrations of CEA were captured on the WP1, whereas the binding of the CEA with Au NP-A2 could be re-leased from the WP2 thanks to the highly affinity of CEA toward A2. The dual signal readout with the 'signal-off' of WP1 and 'signal-on' of WP2 were employed for the spatial-resolved PEC (SR-PEC) strategy to detect CEA as an analytical model. Combining NaYF4:Yb, Er UCNPs@CdTe nanocrystals with spatial-resolved model on 3D printing device, the PEC rati-ometric aptasensor based on steric hindrance effect and exciton-plasmon interactions (EPI) exhibited a linear range from 10.0 pg mL-1 to 5.0 ng mL-1 with a limit of detection of 4.8 pg mL-1 under 980 nm illumination. The SR-PEC ratiometric strategy showed acceptable stability and reproducibility with a superior anti-interference ability. This approach can provide the guidance for the design of ratiometric, multiplexed and point-of-care biosensors.
Hollow heterostructured g-C3N4@CeO2 photocatalysts with rich oxygen vacancies are controllable designed by a facile strategy. The synergetic effect and oxygen vacancies of g-C3N4@CeO2 play the major role in the process of CO2 reduction, leading to CH4 generating much earlier and higher concentration than that of the pristine g-C3N4 and CeO2 alone. Meanwhile, the unique hollow structures can make multiple reflections of light in the cavity, and thus enhance the utilization efficiency of light. Moreover, the L-cysteine offers amine groups and meanwhile is anchored on the surface of g-C3N4 during the synthesis process, and thus contributes greatly to the enhanced CO2 adsorption capability. Additionally, the large CO2 adsorption capability is also beneficial for the enhanced photocatalytic activity. Therefore, the novel photocatalysts exhibit a remarkable reduction performance for CO2 reduction under visible light irradiation. The g-C3N4@CeO2 (CeO2 49.7 wt %) shows the highest yields of CH4 (3.5 μmol g⁻¹), CH3OH (5.2 μmol g⁻¹) and CO (16.8 μmol g⁻¹), which are higher than most of other latest reported g-C3N4 based photocatalysts for CO2 photoreduction, including coupled with semiconductors and noble metal cocatalysts. This strategy might represent a novel way for the effective conversion of CO2 to clean fuels and can also be great potential used in the energy and environmental science.
4-Chlorophenol (4-CP) is a toxic chlorinated organic pollutant that can result in many harmful effects, such as carcinogenesis, teratogenesis, and mutagenesis, and that has recently attracted increasingly widespread attention. Therefore, it is necessary to develop a highly sensitive and selective method for the detection of 4-CP in water. A sensitive photoelectrochemical sensor based on the heterojunction between a BiPO4 nanocrystal and a BiOCl nanosheet (BiPO4/BiOCl) was designed for detecting 4-CP. The BiPO4/BiOCl heterojunction was synthesized via an in situ hydrothermal method with the assistance of ionic liquids (ILs) 1-hex-adecyl-3-methylimidazolium chloride ([C16mim]Cl) and 1-octyl-3-methylimidazolium dihydrogen phosphate ([Omim]H2PO4). Compared to pure BiOCl and pure BiPO4, the BiPO4/BiOCl heterojunction possessed effective separation of photoinduced electron-hole pairs, resulting in enhanced photoelectrochemical performance. When considering this enhanced photoelectrochemical response in terms of 4-CP, the photoelectrochemical sensor that was designed based on the BiPO4/BiOCl heterojunction presented a strong linear relationship, a wide range, a low detection limit, and high repeatability, specificity and stability. Therefore, the photoelectrochemical sensor presented here can be considered an effective analytical method for monitoring 4-CP. This work not only provides a simple synthetic method for the production of BiPO4 nanocrystals, but also broadens the application of BiPO4-based heterojunction materials in photoelectrochemical sensors.
A novel enhanced photoelectrochemical (PEC) DNA biosensor, based on a compact heterojunction g-C3N4/MoS2 and co-sensitization effect with CdSe quantum dots (QDs), was first proposed for simple and accurate analysis of a short ssDNA. In this work, the g-C3N4/MoS2 was successfully synthesized and used as the electrode matrix material to construct PEC biosensor. 2D/2D heterojunction was formed between g-C3N4 and MoS2, which could promote the separation of photogenerated electron-hole pairs resulting in an enhanced photocurrent. In the presence of target DNA, CdSe QDs labeled reporter DNA was complementary pairing with target DNA which was specific recognized by capture DNA loading on self-assembled CdS QDs film, leading to close contact between CdSe QDs and g-C3N4/MoS2 modified electrode surface, thereby resulting in the enhanced photocurrent intensity due to the co-sensitization effect. Under the optimal operating conditions, the photoelectrochemical biosensor demonstrated favorable accuracy and could respond to 0.32 pM (S/N = 3) with a linear concentration range from 1.0 pM to 2.0 μM. Moreover, the proposed PEC DNA biosensor exhibits high sensitivity, excellent specificity, acceptable reproducibility and accuracy, showing a promising potential in DNA bioanalysis and other relative fields.
Developing effective sensing method for trace analysis of ampicillin (AMP) is urgent and significant due to its residue possess serious threats to human health. Herein, a p-n heterojunction, on the basis of p-type BiFeO3 nanoparticles coupled n-typed ultrathin graphite-like carbon nitride (utg-C3N4) nanosheets, has been designed and synthesized via a simple electrostatic interaction strategy. Such p-n heterojunction has two advantages: one is capable to narrow the band gap of photoactive materials from 2.20 eV of BiFeO3 down to 2.04 eV of BiFeO3/utg-C3N4, leading to improve the efficiency of visible light utilization; and the other is to facilitate the charge separation rate, resulting in the boosted photoelectrochemical (PEC) performance of BiFeO3/utg-C3N4. Under visible light illumination, the photocurrent of the resulted BiFeO3/utg-C3N4 was 7.0-fold enhanced than that of pure BiFeO3 nanoparticles, and indeed 2.3-fold enhanced comparing to BiFeO3/bulk-C3N4. Based on excellent PEC properties of BiFeO3/utg-C3N4, an on-off-on PEC aptasensor was successfully fabricated for ampicillin (AMP) determination with highly selectivity and sensitivity. The fabricated PEC aptasensor exhibited excellent PEC performance with a broad linear in the range from 1 × 10–12 mol L–1 to 1 × 10⁻⁶ mol L–1 as well as a low detection limit of 3.3 × 10–13 mol L–1 (S/N = 3), and also good feasibility in real sample. The excellent analytical performance indicated that PEC aptasensor on the basis of the visible light driven BiFeO3/utg-C3N4 heterojunction can provide a promising biosensor platform for sensitive detection AMP in food and environment analysis.
An innovative near-infrared (NIR) light-driven photoelectrochemical (PEC) aptasensor was constructed for sensitive screening of carcinoembryonic antigen (CEA) on the basis of in-situ formation of Ag2S nanoparticles on the NaYF4:Yb,Er upconversion nanoparticles (UCN), coupling with hybridization chain reaction (HCR) for the signal am-plification. Utilization of UCN as the light nanotransducer could convert the NIR light into an applicable wavelength harvested by semiconductors. The multiemissions of NaYF4:Yb,Er UCN could match well with the absorption charac-teristics of Ag2S. In the presence of target CEA, a sandwich-type reaction was carried out between capture CEA ap-tamer/NaYF4:Yb,Er-modified electrode and trigger CEA aptamer, which underwent an unbiased strand-displacement reaction to open C-rich hairpin probes in sequence between two alternating hairpins with the assistance of C-Ag+-C chelation reaction. Upon addition of sulfidion, the chelated Ag+ ions in the long-nicked DNA poly strands by hybridi-zation chain reaction reacted with S2- to generate Ag2S nanoparticles. The formed Ag2S could utilize effectively the upconversion emissions to amplify the photocurrent. Under optimal conditions, NaYF4:Yb,Er-based NIR light-responsive PEC aptasensing platform exhibited high sensitivity for the determination of CEA within a dynamic linear range of 0.005 – 5.0 ng mL-1. The limit of detection was 1.9 pg mL-1. Good precision and high specificity could be ac-quired in this system for the analysis of target CEA. Human serum samples containing target CEA were measured by using our strategy, and received well-matched results relative to human CEA enzyme-linked immunosorbent assay kits. Importantly, NaYF4:Yb,Er-based NIR light-responsive PEC aptasensing system provides a new ideal on the detection of disease-related biomarkers by using nucleic acid-based amplification strategy.
An ultrasensitive label-free photoelectrochemical (PEC) immunosensor with high visible-light activity was developed for quantitative detection of amyloid β-protein (Aβ) by cross-linking anti-Aβ antibody onto the Ag2S sensitized SnO2/SnS2 nanocomposites. Specifically, SnO2 with flower-like porous nanostructure was innovatively applied in PEC immunosensor as a basal material. It could form a heterostructure with SnS2, which brought about the sensitization of SnO2 and enhanced the separation of photogenerated electrons and holes. Moreover, Ag2S was in-situ growth on the surface of SnO2/SnS2, which further enhanced the photocurrent response significantly. Therefore, SnO2/SnS2/Ag2S could form stepwise band-edge structure, which benefited the light harvesting and provided a good foundation for sensor construction and detection. Under optimal conditions, the PEC immunosensor was used to detect the content of Aβ and exhibited a wide linear concentration range from 0.5 pg mL-1 to 100 ng mL-1, with low limit of detection (0.17 pg mL-1) and limit of quantification (0.56 pg mL-1). Additionally, the designed PEC immunosensor exhibited good reproducibility, specificity, and stability which may find potential applications in the biosensor, biomedicine, clinical diagnosis, photocatalysis and other related fields.
Using photoelectrochemical (PEC) platform for ultrasensitive detection of sulfate-reducing bacteria (SRB) is a big challenge since sensor sensitive component can be damaged by corrosive metabolites. In this work, a novel bio-etching strategy for sensitizing PEC platform is developed to detect SRB. In the presence of bacterial metabolite (H2S), BiOCl platform can be bio-etched to form Bi2S3/BiOCl p-n heterojunction, leading to a significant enhancement of photocurrent. The PEC sensing platform fabricated by bio-etching strategy presents acceptable detection specificity and high detection sensitivity with a low detection limit of 29 cfu/mL for SRB. The current work can provide new strategies to sensitize PEC platforms for detection of microorganisms that produce corrosive metabolite.
Previous works on photoelectrochemical (PEC) biosensors have demonstrated that photoanode-based type possesses satisfying sensitivity, because photoanode utilize electrons as the majority charge carriers and a distinct photocurrent can be generated when electron donors are furnished. However, as hole-oxidation reaction occurs at the photoanode interface, photoanode-based PEC sensor has inferior anti-interference capacity to reductive substances coexisting in the biological sample, leading to a challenged selectivity. Herein, a universal design on selectivity-enhanced PEC enzyme sensor was proposed by integrating photoanode with biocathode. Specifically, CuInS2 sensitization layer and ZnS passivation layer were deposited in sequence on the TiO2 film modified indium−tin oxide (ITO) electrode mainly by successive ionic layer adsorption and reaction (SILAR) means, forming the hybrid ZnS/CuInS2/TiO2/ITO photoanode. A carbon fiber paper (CFP) electrode was modified with biocatalysts of enzymes via the assistance of chitosan (CS) to fabricate the biocathode. Utilizing glucose oxidase (GOx) and horserdish peroxidase (HRP) as biocatalysts, a selectivity-enhanced PEC sensor for glucose was developed. The PEC sensing platform integrating photoanode with biocathode not only inherits distinct photocurrent of the photoanode-based sensor; but also possesses enhanced selectivity, because just biocathode was incubated in the biological sample and there is on interaction between photoanode and coexisting reductive substances.
In this work, a new “signal-on” split-type photoelectrochemical (PEC) sensing platform for prostate-specific antigen (PSA) detection was successfully constructed using p-type Cu-doped Zn0.3Cd0.7S as the photosensitive semiconductor material and target-triggered rolling circle amplification (RCA) for signal amplification. The signal derived from Cu-doped Zn0.3Cd0.7S was amplified by hemin/G-quadruplex. Upon target PSA introduction, the aptamer-primer probe (apt-pri) was captured by capture antibody-conjugated magnetic bead (MB-mAb) to form the sandwiched MB-mAb/PSA/apt-pri. The complex could initiate the RCA reaction to produce a long single-stranded DNA that provided binding sites for G-rich DNA and to form long single-stranded DNA/G-quadruplex/hemin. Upon the addition of exonuclease III (Exo III), the hemin/G-quadruplex immobilized on the RCA long product could be released by the digestion of Exo III. The hemin/G-quadruplex complexes in this study were used as efficient electron acceptors to neutralize the photoelectrons generated from the semiconductor and hindered the recombination of charges, thus enhancing the photocurrent. Under the optimum conditions, the developed sensing system displayed a good analytical performance with a linear range of 0.05–40 ng mL⁻¹ PSA and a detection limit of 16.3 pg mL⁻¹. Furthermore, good selectivity, high anti-interference ability, satisfactory reproducibility, and good accuracy were also achieved. These prominent analytical properties revealed that our strategy might be a potential and reliable tool for the detection of PSA.
Utilizing high-energy beta particles emitted from radioisotope for long-lifetime betavoltaic cells is a great challenge due to low energy conversion efficiency (ECE). Here we report a betavoltaic cell fabricated using TiO2 nanotube arrays (TNTAs) electrochemically reduced in ethylene glycol electrolyte (EGECR-TNTAs) for the enhancement of betavoltaic effect. The electrochemical reduction of TNTAs using high cathodic bias in organic electrolytes is indeed a facile and effective strategy to induce in situ self-doping of oxygen vacancy (OV) and Ti3+ defects. The black EGECR-TNTAs is highly stable with a significantly narrower bandgap and higher electrical conductivity as well as UV-Vis-NIR light absorption. A 20 mCi of 63Ni betavoltaic cell based on the reduced TNTAs exhibits maximum ECE of 3.79% with open-circuit voltage of 1.04 V, short-circuit current density of 117.5 nA cm-2, and maximum power density of 39.2 nW cm-2. The betavoltaic enhancement can be attributed to the enhanced charge carrier transport and separation as well as multiple exciton generation of electron-hole pairs due the generation of OV and Ti3+ interstitial bands below the conductive band of TiO2.
In this work, a CuS-TiO2 heterojunction composite was prepared by dispersedly depositing CuS nanoparticles on TiO2 nanospheres surface with a hydrothermal method, and was then used to construct a photoelectrochemical (PEC) aptasensor for sensitive detection of microcystin-LR (MC-LR) in aquatic environment. The energy bands of CuS nanoparticles and spherical anatase TiO2 were well matched, which enhanced the photo-to-current conversion efficiency. The composite exhibited the enhanced visible light absorption, the improved separation of photo-generated charges, and the reduced self-aggregation of CuS nanoparticles, leading to the enhanced photocurrent response. The PEC aptasensor was constructed by immobilizing CuS-TiO2 composite on ITO electrode with chitosan film that further covalently bound aminated aptamer. After the target, microcystin-LR (MC-LR) as an analyte model, was captured by the aptamer on the aptasensor, it could be oxidized by the photo-generated hole to impede the electron-hole recombination and further amplify the photocurrent. The PEC aptasensor showed superior analytical performance for MC-LR with a linear range of 5.0 × 10-5 nM to 250 nM and a detection limit of 2.0 × 10-5 nM. The detection results with the aptasensor for practical water samples indicated its promising application in environmental monitoring.
A novel enhanced photoelectrochemical DNA sensor, based on a TiO2/Au hybrid electrode structure, was developed to detect target DNA. The sensor was developed by successively modifying fluorine-tin oxide (FTO) electrodes with TiO2 nanoparticles, gold (Au) nanoparticles, hairpin DNA (DNA1), and CdSe-COOH quantum dots (QDs), which acted as signal amplification factors. In the absence of target DNA, the incubated DNA1 hairpin and the CdSe-COOH QDs were in close contact with the TiO2/Au electrode surface, leading to an enhanced photocurrent intensity due to the sensitization effect. After incubation of the modified electrode with the target DNA, the hairpin DNA changed into a double helix structure, and the CdSe QDs moved away from the TiO2/Au electrode surface, leading to a decreased sensitization effect and photoelectrochemical signal intensity. This novel DNA sensor exhibited stable, sensitive and reproducible detection of DNA from 0.1 μM to 10 fM, with a lower detection limit of 3 fM. It provided good specificity, reproducibility, stability and is a promising strategy for the detection of a variety of other DNA targets, for early clinical diagnosis of various diseases.
A new double photosystems-based 'Z-scheme' photoelectrochemical (PEC) sensing platform is designed for ultrasensitive detection of prostate-specific antigen (PSA) by coupling with three-dimensional (3D) DNA walker. Two photosystems consist of CdS quantum dots (photosystem I; PS I) and BiVO4 photoactive materials (photosystem II; PS II), whereas gold nanoparticles (AuNPs) photodeposited on high-active {010} facets of BiVO4 are used as the electron mediators to promote electron transfer from conduction band (CB) of PS II to valence band (VB) of PS I. 3D DNA walker-based amplification strategy is carried out between hairpin DNA1 conjugated onto the AuNP, hairpin DNA2 labeled with CdS quantum dot (QD-H2) and DNA walker complementary with the PSA aptamer modified to magnetic bead (Apt-MB). Upon addition of target, DNA walker strand is displaced from DNA walker/Apt-MB to open hairpin DNA1 on AuNP@BiVO4. In the presence of QD-H2, DNA walker induces the hybridization of DNA1 with DNA2 on the gold nanoparticles step by step, thereby resulting in the assembly of CdS QDs on the AuNP@BiVO4 to form 'Z-scheme' double photosystems with strong photocurrent. Under optimum conditions, the 'Z-scheme' PEC sensing system exhibits good photocurrent responses toward target PSA within the working range of 0.01 – 50 ng mL-1 at a low detection limit of 1.5 pg mL-1. Good reproducibility and accuracy are acquired for analysis of target PSA and human serum specimens relative to commercial PSA ELISA kit. Importantly, our strategy provides a new horizon for photoelectrochemical in vitro diagnostics.
In this work, a sensitive photoelectrochemical aptasensor was developed for kanamycin detection using an enhanced photocurrent response strategy, which is based on the surface plasmon resonance effect of gold nanoparticles deposited on a 3D TiO2-MoS2 flower-like heterostructure. A significant aspect of this development lies in the photoelectrochemical and morphological features of the unique ternary composite, which have contributed to the excellent performance of the sensor. To develop an aptasensor, mercapto-group modified aptamers were immobilised on the photoactive composite as a recognition unit for kanamycin. The TiO2-MoS2-AuNP composite was demonstrated to accelerate the electron transfer, increase the loading of aptamers and improve the visible light excitation of the sensor. Under optimal conditions, the aptasensor exhibited a dynamic range from 0.2 nM to 450 nM of kanamycin with a detection limit of 0.05 nM. Overall, we have successfully synergised both the electrical and the optical merits from individual components to form a ternary composite, which was then demonstrated as an effective scaffold for the development of PEC biosensors.
As a broad-spectrum antibiotic, tetracycline (TC) is widely used in agricultural purposes and human therapy. More attention is paid to TC as a serious threat to human health, including the fast spreading of antibiotic resistance gene and the serious toxicity to aquatic organisms. Therefore, the timely and accurate determination of TC residues is an urgent task to protect the safety of human. Herein, an effective and facile photoelectrochemical sensor platform based on carbon nitride/bismuth oxyhalide (CN/BiOBr) composites can be constructed for monitoring TC. The flower-like CN/BiOBr composites are prepared via a simple one-pot ethylene glycol-assisted solvothermal process with the addition of ionic liquid 1-hexadecyl-3-methylimidazolium bromide ([C16mim]Br). In view of matched energy band positions of CN and BiOBr, the addition of CN can reduce the recombination of photogenerated electron-hole pairs and improve the efficiency of visible light utilization, leading to enhancing photoelectrochemical response of BiOBr. Under light excitation, the photocurrent of CN/BiOBr composites is drastically improved, which is 6 times as much as that of pure BiOBr. Considering the superior photoelectrochemical performance, a photoelectrochemical sensor for monitoring TC has been developed, displaying linearly enhanced photocurrent with increasing the TC concentration. Two linear relationships received are from 8.0 to 4.0 × 102 ng mL-1, and 4.0 × 102 to 5.2 × 103 ng mL-1, respectively. The detection limit is 3.8 ng mL-1. The photoelectrochemical sensor exhibits a series of benefits including excellent stability, a wide linear range, a low detection limit and good anti-interference ability. Therefore, this work may offer great promises in providing a universal and efficient photoelectrochemical sensor for the tetracycline detection, and pave the way of constructing more materials used in photoelectrochemical detection field.
In this study, we developed a novel photoelectrochemical (PEC) sensor for the highly sensitive detection of erythromycin by functionalising graphene oxide (GO) with nickel tetra-amined phthalocyanine (NiTAPc) through covalent bonding, which resulted in the formation of NiTAPc-Gr. The fabricated sensor showed a higher PEC efficiency under blue light, exhibiting a peak wavelength of 456 nm, as compared to that of the monomer. Further, the NiTAPc-Gr/indium tin oxide (ITO) sensor exhibited a photocurrent that was 50-fold higher than that for a GO/ITO sensor under the same conditions. Under optimal conditions, the NiTAPc-Gr PEC sensor showed a linear response for erythromycin concentrations ranging from 0.40 to 120.00 μmol L-1, with the minimum limit for detection being 0.08 μmol L-1. Thus, the NiTAPc-Gr sensor exhibited superior performance and excellent PEC characteristics, high stability, and good reproducibility with respect to the sensing of erythromycin. Moreover, it is convenient to use, fast, small, and cheap to produce. Hence, it should find wide use in the analysis of erythromycin in real-world applications.
In this work, a sensitive potentiometric resolved ratiometric photoelectrochemical aptasensor for Escherichia coli (E. coli) detection was successfully fabricated with non-metallic nanomaterials. To avoid the use of precious metals or heavy metals, three-dimensional graphene hydrogel-loaded carbon quantum dots (C-dots/3DGH) and graphene-like carbon nitride (g-C3N4) with excellent PEC activity and matched potential were prepared. These two materials were modified onto two adjacent areas on the ITO electrode. By applying different bias voltage, the cathodic current generated by C-dots/3DGH and the anodic current generated by g-C3N4 can be clearly distinguished and would not interfere with one another. Then E. coli aptamer was modified onto the surface of C-dots/3DGH. In the presence of targets, the binding of E. coli with aptamer lead to the steric hindrance greatly increased and the cathodic current decreased significantly. Meanwhile, the anodic current generated by g-C3N4 was not influenced and it can serve as a stable reference to evaluate the environmental factors. Therefore, the concentration of E. coli can be quantified by the ratio of cathodic current to anodic current, which can effectively eliminate these analyte-independent factors and provide a more precise analysis. In addition, this ratiometric PEC biosensor also showed a good sensitivity and a wide linear range (2.9 cfu/mL to 2.9 × 106 cfu/mL).
A novel label-free photoelectrochemical (PEC) sensor based on graphene quantum dots doped with nitrogen and sulfur (N,S-GQDs) and CdS co-sensitized hierarchical Zn2SnO4 cube was fabricated to detect cardiac troponin I (cTnI). The unique hierarchical Zn2SnO4 cube was synthesized successfully by the solvothermal method, which has a large specific surface to load functional materials. N,S-GQDs nanoparticles were assembled to the surface of cubic Zn2SnO4 coated ITO electrode, which efficiently accelerated the electronic transition and improved photo-to-current conversion efficiency. Then, CdS nanoparticles further were modified by in-situ growth method to form Zn2SnO4/N,S-GQDs/CdS composite with prominent photocurrent, which was 30 times that of the Zn2SnO4 cube alone. In this work, the specific immune recognition between cTnI antigens and cTnI antibodies (anti-cTnI) reduced the intensity of the photoelectric signal. And the intensity decreased linearly with the logarithm of cTnI concentration range from 0.001 ng/mL to 50 ng/mL with a detection limit of 0.3 pg/mL. With high sensitivity, excellent selectivity, good stability and reproducibility, the fabricated PEC sensor showed promising applications in the sensor, clinical diagnosis of myocardial infarction and PEC analysis.
A novel photoelectrochemical (PEC) aptasensor based on cerium (Ce) doped CdS modified graphene (G)/BiYWO6 was designed, which exhibits enhanced PEC intensity compared with pure BiYWO6, G/BiYWO3 and BiYWO6/Ce:CdS. In this scenario, ascorbic acid (AA) was exploited as an efficient and non-poisonous electron donor for scavenging photogenerated holes. The doping of Ce in CdS promoted its visible light absorption range and facilitated the charge transfer rate as well as hindered the h+/e- recombination. Moreover, the combination of G further promoted the electron carrier separation and transfer process due to its excellent electron collection and shuttling characteristic. Thus, the G/BiYWO6/Ce:CdS heterostructure was successfully served as a matrix for the PEC detection of tetracycline (Tc) at 0 V (vs Hg/Hg2Cl2). Under optimal conditions, the PEC aptasensor could offer a sensitive and specific detection limit (3 S/N) of Tc down to 0.01 ng/mL, as well as acceptable reproducibility, selectivity and storage stability, which opened up a promising pathway for the development of PEC biosensors.
Ti³⁺ self-doped TiO2/g-C3N4 mesostructured nanosheets heterojunctions (Ti³⁺-TiO2/Meso-g-C3N4) have been prepared via calcination-sonication assisted method using amino cyanamide as precursors, combined with a solid-state chemical reduction method. The Ti³⁺-TiO2/Meso-g-C3N4 heterojunctions with narrow band gap of ∼2.21 eV possess relative high surface area of ∼73.8 m² g⁻¹, and large pore size of ∼10 nm. Remarkably, the Ti³⁺-TiO2/Meso-g-C3N4 heterojunctions exhibit excellent visible-light-driven photocatalytic activity for degradating phenol in wastewaters. The photocatalytic hydrogen production rate of Ti³⁺-TiO2/Meso-g-C3N4 heterojunctions rise to ∼290.2 μmol h⁻¹ g⁻¹, which is about 4 and 14 times higher than that of the bare Meso-g-C3N4 and TiO2, respectively. The enhanced photocatalytic activity may be ascribed to the synergetic effect of the mesoporous structure providing sufficient surface active sites, and Ti³⁺ self-doping and the formed heterojunctions promoting the spatial separation of photogenerated electron-hole pairs.
A direct formatted photoelectrochemical (PEC) aptasensing platform was constructed for ultrasensitive microcystin-LR (MC-LR) detection with AgI-nitrogen-doped graphene (AgI-NG) composites as photocathode and aptamer as recognition element. The photocurrent of the AgI-NG composites was about 10.9 times higher than that of AgI. Furthermore, to investigate the sensing mechanism, the experiments with photoluminescence (PL) and time-correlated single-photon counting (TCSPC) technique were implemented as supporting evidence. The developed aptasensor can be used for MC-LR detection in fish samples. The experimental and theoretical efforts elucidate that the theory of flow directions of electron give reasonable explanation for the sensing process: prevailing electron-hole recombination constitutes a signal-off strategy, while electron transfer playing the leading role presents a signal-on performance. Impressively, we discovered that the sensing mechanism differed significantly when applied to the same analyte despite the commonality among the detecting configuration themselves, which is dependent by the interaction between the analyte MC-LR and transducer. For the detection process, in the presence of MC-LR, the specific recognition of the targets with the sensing interface would trigger the formation of the aptamer/MC-LR complex, resulting in reduced electron transfer rate, increased charge recombination, and hence quenched photocurrent intensity of the AgI-NG with detection limits of 0.017 pM. This work will help to complement the vital theoretical explanation about the underlying sensing mechanism, and future designing of PEC aptasensors.
Herein, novel photoactive materials, nitrogen-doped porous carbon-ZnO (NPC-ZnO) nanopolyhedra, were prepared by direct carbonization of ZIF-8 nanopolyhedra in a nitrogen atmosphere. The morphology, structure and photoelectrochemical (PEC) properties were characterized by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, nitrogen adsorption-desorption method, and PEC methods. The results showed that the obtained NPC-ZnO nanopolyhedra had rhombic dodecahedron morphology with uniform particle size of about 100 nm and high surface area of 609.2 m2 g-1. Under visible light irradiation, the NPC-ZnO nanopolyhedra showed better PEC performance than ZnO nanorod and ZIF-8 nanopolyhedra in aqueous media with dissolved oxygen and ascorbic acid (AA). Taking alkaline phosphatase (ALP) as a model, a NPC-ZnO nanopolyhedra-based PEC sensor was developed and showed good performance for ALP assay with a wide linear response range from 2 to 1500 U L-1 and a low detection limit of 1.7 U L-1. Moreover, the PEC sensor possessed acceptable selectivity, reproducibility and stability. The prepared NPC-ZnO nanopolyhedra provide a new photoactive material for construction of PEC sensors and may have promising applications in PEC assay of heavy metal ions, organic pollutants and biomolecules.
High sensitivity of biosensor is one of the most important factor to realize the accurate detection of biomarkers. To achieve this purpose, enhancing initial signal and amplifying the value of signal change are two main approaches. In this study, a novel signal-off photoelectrochemical (PEC) immunosensor for highly sensitive determination of insulin was developed upon dual inhibition effect of CuS-SiO2 composites toward CdS sensitized carbon doped titanium dioxide (C-TiO2/CdS). Due to the doping of carbon and sensitization of CdS, C-TiO2/CdS sensitized structure was employed as ideal photoactive matrix, which provided stable and enhanced basal signal. To achieve the amplification of signal change value, CuS-SiO2 composites were prepared and used as labels. On account of the competitively light harvesting and electron donors consuming by p-type semiconductor CuS, less light energy and electron donors arrived at the C-TiO2/CdS sensitized structure. Besides, the remarkable steric hindrance effect of CuS-SiO2 labeled secondary antibodies (CuS-SiO2-Ab2) conjugates obstructed the transfer of electrons and diffusion of the electron donors to the photoelectrode surface, leading to further decrease of photocurrent compared with the pure CuS nanoparticles. Greatly enhanced sensitivity is achieved due to the dual inhibition effect of CuS-SiO2 composites on C-TiO2/CdS. Taking advantage of the synergy effect of C-TiO2/CdS sensitized structure and dual inhibition effect of CuS-SiO2-Ab2 bioconjugates, the as-prepared immunosensor for insulin exhibited high sensitivity and good stability with a low detection limit of 0.03 pg mL⁻¹. Additionally, the strategy provided an efficient and simple approach for signal amplification and held great promise for other PEC immunoassay development.
A novel photoelectrode of three-dimensional (3D) lupinus-like TiO2 nanorod@Sn3O4 nanosheet hierarchical heterostructured arrays (TiO2@Sn3O4 HHAs) on transparent FTO glass substrate was designed and fabricated by a two-step solvothermal growth process. Photoelectrochemical(PEC) measurements showed that 3D lupinus-like TiO2@Sn3O4 HHAs photoelectrode displayed enhanced photocurrent density (3-fold increase with respect to pure TiO2), improved conversion efficiency, more negative onset potential (from -0.13 to -0.33 V vs normal hydrogen electrode (NHE)), and higher light on/off cycle stability. The improved PEC properties may be ascribable to the enhancement of light harvesting and large contact area with the electrolyte by increased surface area as well as improvement of charge transfer and collection through the synergistic effects between band structures and morphology.
A novel signal-amplified strategy based on dopamine-loaded liposome (DLL) was developed for competitive-type non-enzymatic photoelectrochemical (PEC) immunoassay of small- molecular aflatoxin B1 (AFB1) in foodstuff, using Mn2+-doped Zn3(OH)2V2O7•2H2O nanobelts. The signal was amplified by high-loaded capacity of liposome and high-efficient dopamine molecule to enhance photocurrent of Mn2+-doped Zn3(OH)2V2O7•2H2O nanobelts. The loaded dopamine in the liposome was used as an electron donor to scavenge the hole and inhibit the charge recombination. To design such an immunoassay system, AFB1-bovine serum albumin (AFB1-BSA) conjugate was covalently bound with the multifunctional liposome via the cross-linkage glutaraldehyde, whereas monoclonal anti-AFB1 antibody was labeled onto magnetic bead by typical carbodiimide coupling. Upon addition of target AFB1, a competitive immunoreaction was carried out between the analyte and the AFB1-BSA-DLL for the conjugated antibody on the magnetic bead. Followed by magnetic separation, the carried DLL on the magnetic beads was lysed by using Triton X-100 to release the encapsulated dopamine. The as-produced dopamine (as an elector donor) increased the photocurrent of the Mn2+-doped Zn3(OH)2V2O7•2H2O nanobelts. The photocurrent depended on the as-released amount of the dopamine. The change in the photocurrent enhanced with the increasing AFB1 concentration. Under the optimal conditions, Mn2+-doped Zn3(OH)2V2O7•2H2O nanobelts exhibited good photoelectrochemical responses for the detection of AFB1, and allowed the detection of AFB1 at a concentration as low as 0.3 pg mL-1 within a linear range from 0.5 pg mL-1 to 10 ng mL-1. Importantly, this system provided an ideal PEC immune sensing platform based on Mn2+-doped Zn3(OH)2V2O7•2H2O nanobelts and the high-loaded liposome for the detection of small molecules.
The idea that single metal atoms dispersed on a solid support can act as an efficient heterogeneous catalyst was raised in 2011 when single Pt atoms on an FeOx surface were reported to be active for CO oxidation and preferential oxidation of CO in H2. The last six years have witnessed tremendous progress in the field of single-atom catalysis. Here we introduce the major achievements on this topic in 2015 and 2016. Some particular aspects of single-atom catalysis are discussed in depth, including new approaches in single-atom catalyst (SAC) synthesis, stable gold SACs for various reactions, the high selectivity of Pt and Pd SACs in hydrogenation, and the superior performance of non-noble metal SACs in electrochemistry. These accomplishments will encourage more efforts by researchers to achieve the controllable fabrication of SACs and explore their potential applications. © 2017 Dalian Institute of Chemical Physics, the Chinese Academy of Sciences