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Analytical applications of carbon dots in forensics, security, and other related fields
Abstract
Fluorescent carbon dots (CDs) with stable physicochemical properties are one of the fascinating classes of carbon nanomaterials that have small particle size and distinctive optical properties added widespread attention in recent years. Along with the unique optical properties such as high photoluminescence, photo-bleaching resistance, and light stability, CDs have the promising advantages of low cost, good biocompatibility, environmental friendliness, and easy functionalization. Moreover, CDs can surface passivation and functionalization with other types of materials to get the nanostructured composites with outstanding properties, which offer new visions and concepts for the research of several fields. Hence, CDs are promising nanomaterials for chemical sensing, biological imaging, nanomedicine, photocatalysis, adsorption treatment, and electrocatalysis. This chapter details contribution of CDs in forensic, security, and other related analytical applications. It is likely to offer a significant guidance for the further study of CDs in the field of forensic science and detection.
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Zero-dimensional (0D) nanomaterials, including graphene quantum dots (GQDs), carbon quantum dots (CQDs), fullerenes, inorganic quantum dots (QDs), magnetic nanoparticles (MNPs), noble metal nanoparticles, upconversion nanoparticles (UCNPs) and polymer dots (Pdots), have attracted extensive research interest in the field of biosensing in recent years. Benefiting from the ultra-small size, quantum confinement effect, excellent physical and chemical properties and good biocompatibility, 0D nanomaterials have shown great potential in ion detection, biomolecular recognition, disease diagnosis and pathogen detection. Here we first introduce the structures and properties of different 0D nanomaterials. On this basis, recent progress and application examples of 0D nanomaterials in the field of biosensing are discussed. In the last part, we summarize the research status of 0D nanomaterials in the field of biosensing and anticipate the development prospects and future challenges in this field.
Carbon dots (CDs) have received significant attention worldwide from the beginning of this century, and recently, it has bloomed in every branch of applied sciences. Because of their outstanding physical and chemical properties together with biocompatibilities, CDs find a wide spectrum of applications in drug delivery, explosive detection, chemical sensing, food safety, bioimaging, energy conversion, photocatalysis, etc. This brief review is focused on the synthesis of CDs and their applications. The photophysical properties of CDs are also discussed herewith.
Sensitive and selective assays are demanded for quantitation of new psychoactive substances such as 4-chloroethcathinone that is a π-conjugated keto compound. Carbon dots (C-dots) prepared from L-arginine through a hydrothermal route have been used for quantitation of 4-chloroethcathinone in aqueous solution and on C-dot-functionalized papers (CDFPs). To prepare CDFPs, chromatography papers, each with a pattern of 8 × 12 circles (wells), are first fabricated through a solid-ink printing method and then the C-dots are coated into the wells. π-Conjugated keto or ester compounds induce photoluminescence quenching of C-dots through an electron transfer process. At pH 7.0, the CDFPs allow screening of abused drugs such as cocaine, heroin and cathinones. Because of poor solubility of heroin and cocaine at pH 11.0, the C-dot probe is selective for cathinones. The C-dots in aqueous solution and CDFPs at pH 11.0 allow quantitation of 4-chloroethcathinone down to 1.73 mM and 0.14 mM, respectively. Our sensing system consisting of a portable UV-lamp, a smartphone and a low-cost CDFP has been used to detect cathinones, cocaine and heroin at pH 7.0, showing its potential for screening of these drugs in crime sites.
Abstract Fluorescent carbon dots (CDs) including carbon quantum dots (CQDs) and graphene quantum dots (GQDs) have drawn great interest because of their low cost and low toxicity, and they represent a new class of carbon materials prepared by simple synthetic routes. In particular, the optical properties of CDs can be easily tuned by the surface passivation of the organic layer and functionalization of the CDs. Based on the advantages of these carbon materials, CQDs and GQDs have been applied in various fields as nanoplatforms for sensing, imaging, and delivery. In this review, we discuss several synthetic methods for preparing CQDs and GQDs, as well as their physical properties, and further discuss the progress in CD research with an emphasis on their application in heavy metal sensing.
Carbon dots (CDs) display tunable photoluminescence and excitation-wavelength dependent emission. The color of fluorescence is affected by electronic bandgap transitions of conjugated π-domains, surface defect states, local fluorophores and element doping. In this review (with 145 refs.), the studies performed in the past 5 years on the relationship between the fluorescence mechanism and modes for modulating the emission color of CDs are summarized. The applications of such CDs in sensors and assays are then outlined. A concluding section then gives an outlook and describes current challenges in the design of CDs with different emission colors.
Graphical abstractSchematic representation of the relationship between the color-emitting (blue, green, yellow, red and multicolor) modulation of carbon dots and fluorescence mechanism including bandgap transitions of conjugated π-domains and surface defect states.
An ideal anti-counterfeiting technique has to be inexpensive, mass-producible, nondestructive,
unclonable and convenient for authentication. Although many anti-counterfeiting
technologies have been developed, very few of them fulfill all the above requirements. Here
we report a non-destructive, inkjet-printable, artificial intelligence (AI)-decodable and
unclonable security label. The stochastic pinning points at the three-phase contact line of the
ink droplets is crucial for the successful inkjet printing of the unclonable security labels. Upon
the solvent evaporation, the three-phase contact lines are pinned around the pinning points,
where the quantum dots in the ink droplets deposited on, forming physically unclonable
flower-like patterns. By utilizing the RGB emission quantum dots, full-color fluorescence
security labels can be produced. A convenient and reliable AI-based authentication strategy is
developed, allowing for the fast authentication of the covert, unclonable flower-like dot
patterns with different sharpness, brightness, rotations, amplifications and the mixture of
these parameters.
Nanosensors with high sensitivity utilize electrical, optical, and acoustic properties to improve the detection limits of analytes. The unique and exceptional properties of nanomaterials (large surface area to volume ratio, composition, charge, reactive sites, physical structure and potential) are exploited for sensing purposes. High-sensitivity in analyte recognition is achieved by preprocessing of samples, signal amplification and by applying different transduction approaches. In this review, types of signals produced and amplified by nanosensors (based on transducers) are presented, to sense exceptionally small concentrations of analytes present in a sample. The use of such nanosensors, sensitivity and selectivity can offer different advantages in biomedical applications like earlier detection of disease, toxins or biological threats and create significant improvements in clinical as well as environmental and industrial outcomes. The emerging discipline of nanotechnology at the boundary of life sciences and chemistry offers a wide range of prospects within a number of fields like fabrication and characterization of nanomaterials, supramolecular chemistry, targeted drug supply and early detection of disease related biomarkers.
Conventional optical security devices provide authentication by manipulating a specific property of light to produce a distinctive optical signature. For instance, microscopic colour prints modulate the amplitude, whereas holograms typically modulate the phase of light. However, their relatively simple structure and behaviour is easily imitated. We designed a pixel that overlays a structural colour element onto a phase plate to control both the phase and amplitude of light, and arrayed these pixels into monolithic prints that exhibit complex behaviour. Our fabricated prints appear as colour images under white light, while projecting up to three different holograms under red, green, or blue laser illumination. These holographic colour prints are readily verified but challenging to emulate, and can provide enhanced security in anti-counterfeiting applications. As the prints encode information only in the surface relief of a single polymeric material, nanoscale 3D printing of customised masters may enable their mass-manufacture by nanoimprint lithography.
Heavy metal detection has become very important for the protection of water resource. In this work, a novel controllable probe is presented for the sensitive detection of Pb²⁺ in aqueous solutions. The probe was synthesized via the immobilization of surface functionalized carbon dots (named as CAEA-Hs) into the shell of the spherical polyelectrolyte brushes (SPB). The fluorescence of CAEA-H was firstly “turned off” via electrostatic interaction induced quenching. Based on the aggregation induced emission enhancement (AIEE), the fluorescence of the immobilized CAEA-H could be specifically turned on via the aggregation of the SPB particles. This fluorescence “turn on” sensor could selectively detect Pb²⁺ among five different metal ions with a relatively wide detecting range (0–1.67 mM) and good linear relationship (R² = 0.9958). Moreover, the aggregating behavior and nano-structure of CAEA-H loaded SPB have been systematically analyzed via small angle X-ray scattering, turbidity titration, and Zeta-potential measurement. Based on a series of control experiments, we finally gain an insight into the sensing mechanism of this novel sensing probe. This contributed a proof of concept demonstration that sensitive and selective chemical detection can be achieved via a C-dot/SPB synergistic platform.
Apparently mundane, amorphous nanostructures of carbon have optical properties which are as exotic as their crystalline counterparts. In this work we demonstrate a simple and inexpensive mechano-chemical method to prepare bulk quantities of self-passivated, amorphous carbon dots. Like the graphene quantum dots, the water soluble, amorphous carbon dots too, exhibit excitation-dependent photoluminescence with very high quantum yield (~40%). The origin and nature of luminescence in these high entropy nanostructures are well understood in terms of the abundant surface traps. The photoluminescence property of these carbon dots is exploited to detect trace amounts of the nitro-aromatic explosive - 2,4,6-trinitrophenol (TNP). The benign nanostructures can selectively detect TNP over a wide range of concentrations (0.5 to 200 µM) simply by visual inspection, with a detection limit of 0.2 µM, and consequently outperform nearly all reported TNP sensor materials.
Carbon dots (C-dots) are a new class of carbon nanomaterials having size of less than 10 nm. C-dots have been emerged as a star in field of fundamental and technical importance due to its alluring properties. Here in this paper, we have described synthetic routes for fabrication of C-dots. There are several methods for the synthesis of carbon dots, but in this report we have mainly emphasized on hydrothermal, solvothermal and microwave methods. Since these methods are very simple, fast, cost-effective and also do not require very high temperature hence energy efficient and environment friendly. The toxicity concerns can also be overcome with use of green precursors. These methods have also proved very efficient in upgradation of waste material and up cycling of negatively valued product into valuable product. Properties of C-dots such as structure, optical properties, chemiluminescence, electochemiluminescence, in vitro and in vivo toxicity have been briefly discussed. Further, applications of C-dots in biomedical field and environment concern have also been discussed.
Carbogenically coated silica nanoparticles (C-SiO2) exhibit color-tunability and carry great promise for two important forensic applications. First, the C-SiO2 nanopowders are ideal for fingerprint development, yielding strong contrast against multicoloured and patterned backgrounds. Second, spontaneous nanoparticle aggregation leads to non-duplicable, inexpensive nanotags that can support sustainable technologies to combat counterfeiting.
We demonstrate for the first time a wearable biochemical sensor for monitoring alcohol consumption through the detection and quantification of a metabolite of ethanol, ethyl glucuronide (EtG). We designed and fabricated two co-planar sensors with gold and zinc oxide as sensing electrodes. We also designed a LED based reporting for the presence of EtG in the human sweat samples. The sensor functions on affinity based immunoassay principles whereby monoclonal antibodies for EtG were immobilized on the electrodes using thiol based chemistry. Detection of EtG from human sweat was achieved through chemiresistive sensing mechanism. In this method, an AC voltage was applied across the two coplanar electrodes and the impedance across the sensor electrodes was measured and calibrated for physiologically relevant doses of EtG in human sweat. EtG detection over a dose concentration of 0.001-100 μg/L was demonstrated on both glass and polyimide substrates. Detection sensitivity was lower at 1 μg/L with gold electrodes as compared to ZnO, which had detection sensitivity of 0.001 μg/L. Based on the detection range the wearable sensor has the ability to detect alcohol consumption of up to 11 standard drinks in the US over a period of 4 to 9 hours.
Fluorescent carbon dots (CDs) are a novel type of fluorescent nanomaterials, which not only possess the specific quantum confinement effects of nanomaterials due to the small size of nanomaterials, but also have good biocompatibility and high fluorescence. Meanwhile, fluorescence CDs overcome the shortcomings of high toxicity of traditional nanomaterials. Moreover, the preparation procedure of fluorescent CDs is simple and easy. Therefore, fluorescent CDs have great potential applied in photocatalysis, biochemical sensing, bioimaging, drug delivery, and other related areas. In this paper, recent hot researches on fluorescent CDs are reviewed and some problems in the progress of fluorescent CDs are also summarized. At last, a future outlook in this direction is presented.
Amine-functionalized carbon dots (A-CDs) were synthesized by one-step hydrothermal reaction of urea and citric acid. The purified CD sample exhibits a surface states dominated fluorescence emission with a quantum yield of 30%. The A-CDs demonstrate excellent sensitivity toward methamphetamine pre-precursor and precursor, and a remarkable selectivity against common drug cutting agents (diluents) such as Aspirin, Paracetamol, etc. The specific selectivity of CDs towards such type of drug precursor molecules is first time reported, which appears to be related to the spatial distribution of the surface functional groups. The fluorescence-based sensing mechanism is revealed by a detailed analysis on the static and dynamic fluorescence behaviour. We further demonstrated an immobilization strategy for fabricating solid-state sensors, and the retained sensitivity of the A-CDs after immobilization. The study reveals the potential of the use of a CDs as an effective sensing probe for illicit drugs, which is in demand.
In this paper, the importance of modern technology in forensic investigations is discussed. Recent technological developments are creating new possibilities to perform robust scientific measurements and studies outside the controlled laboratory environment. The benefits of real-time, on-site forensic investigations are manifold and such technology has the potential to strongly increase the speed and efficacy of the criminal justice system. However, such benefits are only realized when quality can be guaranteed at all times and findings can be used as forensic evidence in court. At the Netherlands Forensic Institute, innovation efforts are currently undertaken to develop integrated forensic platform solutions that allow for the forensic investigation of human biological traces, the chemical identification of illicit drugs and the study of large amounts of digital evidence. These platforms enable field investigations, yield robust and validated evidence and allow for forensic intelligence and targeted use of expert capacity at the forensic institutes. This technological revolution in forensic science could ultimately lead to a paradigm shift in which a new role of the forensic expert emerges as developer and custodian of integrated forensic platforms.
© 2015 The Author(s) Published by the Royal Society. All rights reserved.
Classification, chemistry, and applications of fullerenes, carbon dots, nanotubes, graphene, nanodiamonds, and combined superstructures of a range of carbon nanoallotropes are investigated. The investigations also cover superstructures consisting of combinations of carbon nanoallotropes such as fullerene aggregates, CNTs or graphene thin films, fibers, membranes, and aerogels in addition to describing individual carbon nanoallotropes. The issue of chemical modification of carbon nanoallotropes with division into several sections based on the origins of the chemical reactivity in each case is also investigated.
In this work, for the first time, novel polyaniline/carbon dots (PANI/Cdots) nanocomposites have been synthesized by a simple method. Meanwhile, the bright fluorescence of Cdots is effectively quenched by PANI through fluorescence resonance energy transfer. With the addition of Hg2+, the strong binding ability between Hg2+ and amino groups of PANI makes the Cdots be released break away from the PANI, resulting in restoration of Cdots fluorescence, which constructs a fluorescent probe for Hg2+ detection. This fluorescence “off-on” signal is sensitive to the concentration of Hg2+, and there is a good linear relationship between the fluorescence intensity of Cdots and the Hg2+ concentrations in the range from 0.05 to 1.0 µM. The detection limit for Hg2+ at a concentration is 0.8 nM. Moreover, it turns out that the nanoprobes represent a rather high selectivity for Hg2+ detection. We believe the PANI/Cdots composites will emerge a new class of fluorescence materials that could be very likely to be suitable for practical application.
Background
Product counterfeiting is growing in scope, scale, and threat. This includes awareness of deceptive and non-deceptive counterfeiting types. (This paper does not consider copyright or digital piracy, currency counterfeiting, fraudulent documents, or artwork forgery.) In response, many organizations are focusing on product counterfeiting including INTERPOL, International Standards Organization, World Health Organization, World Customs Organization, and the U.S. Department of Justice. The goal of this research is to help brand owners and agencies efficiently select appropriate countermeasures including overt, covert and forensic packaging features, as well as functions of market monitoring, modifying supply chains, enforcement, prosecution and legislation.
In this paper, a simple and sensitive fluorescent sensor for methyl parathion is developed based on l-tyrosine methyl ester functionalized carbon dots (Tyr-CDs) and tyrosinase system. The carbon dots are obtained by simple hydrothermal reaction using citric acid as carbon resource and l-tyrosine methyl ester as modification reagent. The carbon dots are characterized by transmission electron microscope, high resolution transmission electron microscopy, X-ray diffraction spectrum, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The carbon dots show strong and stable photoluminescence with a quantum yield of 3.8%. Tyrosinase can catalyze the oxidation of tyrosine methyl ester on the surface of carbon dots to corresponding quinone products, which can quench the fluorescence of carbon dots. When organophosphorus pesticides (OPs) are introduced in system, they can decrease the enzyme activity, thus decrease the fluorescence quenching rate. Methyl parathion, as a model of OPs, was detected. Experimental results show that the enzyme inhibition rate is proportional to the logarithm of the methyl parathion concentration in the range 1.0×10−10–1.0×10−4 M with the detection limit (S/N=3) of 4.8×10−11 M. This determination method shows a low detection limit, wide linear range, good selectivity and high reproducibility. This sensing system has been successfully used for the analysis of cabbage, milk and fruit juice samples.
In this report, we successfully developed a simple and fast MW-assisted method for preparing CDs with strong solid-state fluorescence (SSF) by using phthalic acid and piperazine as precursors. The prepared p-CDs can be obtained in high yield (48.7%) and emit bright yellow-green SSF under 365 nm UV light. The absolute PL quantum yield (PLQY) of p-CDs in solid state was measured to be 20.5%, which is much higher than that in aqueous solution. This interesting phenomenon shows that p-CDs not only successfully conquer the aggregation-caused fluorescence quenching (ACQ) effect, but also achieve enhanced fluorescence emission, which was rarely reported in previous literatures as CDs in solid state always reduce their fluorescence emission due to the excessive resonance energy transfer (RET) or direct π-π interactions. In addition, the relationship between the feed ratio of precursors and optical properties of the CDs were also investigated detailedly. Based on their strong SSF, the p-CDs were successfully used in rapid latent fingerprints detection and white light-emitting diodes (WLEDs) preparation with high quality. In summary, this research not only developed a new type of CDs with strong enhanced SSF, but also offered a valuable reference for design SSF-emitting CDs with high yield.
Great advances have been made on the sensor based methods for the chemical analysis owing to their high sensitivity, selectivity, less testing time, and minimized usage of chemical reagents. Quantum Dots (QDs) having excellent optical properties are highly explored for variety of scientific applications where light plays an important role. In recent years, there have been increasing number of publications on the applications of QDs as photoluminescent nanosensor for the detection of chemical and biomolecules. However, there is hardly any publication describing the usage of QDs in the detection of various toxic chemicals at one place. Hence, a literature survey is made on the applications of QDs as chemosensor in the detection of gaseous, anionic, phenolic, metallic, drug-overdose and pesticide poison so as to open a new perspective towards the role of sensors in the analytical toxicology. In this review, the QDs based analysis of biospecimens for poisonings in clinical and forensic toxicology laboratories is highlighted.
This work comprehensively reviews some fundamental concepts about explosives and their two commonly used classifications based on either their velocity of detonation or their application. These classifications are highly useful in the military/legal field, but completely useless for the chemical determination of explosives. Because of this reason, a classification of explosives based on their chemical composition is comprehensively revised, discussed and updated. This classification seeks to merge those dispersed chemical classifications of explosives found in literature into a unique general classification, which might be useful for every researcher dealing with the analytical chemical identification of explosives. In the knowledge of the chemical composition of explosives, the most adequate analytical techniques to determine them are finally discussed.
Synthesis of red emissive carbon dots (CDs) are highly desirable for sensing application, still remaining bottlenecks in terms of precursor synthesis and product purification. Herein, we have designed a new strategy of realizing efficient red emissive CDs optimal emission at 610 nm (fluorescence quantum yield ca. 24.0 %) based on solvothermal treatment of citric acid and thiourea using dimethylformamide as solvent. Further investigations reveal that the conjugating sp2-domain controlling, the incorporation of nitrogen and surface engineering are mainly responsible for the obtained red-emission of CDs. Taking advantage of optical properties and abundant surface functional groups, CDs were considered to facilely construct ratiometric fluorescent platform for quantifying trace-level organophosphorus pesticides (OPs). Combining acetylcholinesterase-mediated the polymerization of dopamine and the inhibition of pesticide toward enzyme, the degree of polymerization of dopamine rationally depend on the concentration of OPs. By measuring the fluorescence intensity ratio, the proposed platform exhibited highly selective and robust performance toward OPs, displaying ultrasensitive recognition in pg L-1 level. The multi-excitation format could efficiently shield background interference from complex samples by introducing a self-calibrated reference signal, which afford accurate and reliable quantitative information, endowing CDs as a universal candidate for biosensing application by combining target-specific recognition elements.
The realization of long-wavelength emissions and thoroughly understanding of photoluminescence (PL) mechanism are still huge challenges to be addressed for further development of carbohydrate-derived carbon dots (CDs). Herein, novel CDs with excellent green emission were synthesized from a precursor comprising of xylose and m-phenylenediamine in phosphoric acid solution via a simple microwave-assisted hydrothermal method. The PL efficiency was dependent on the combination of different acids and the precursor as well as the synthesis temperature, while the PL properties were mainly related to the acid base environment of precursor. Optical performance and structural characterization revealed that the oxygen-containing groups and protonated amino groups were mainly responsible for the blue and green emission properties, respectively. Moreover, a multi-center fluorescent mechanism on the different PL performances of xylose-derived CDs was proposed and verified by further investigating the pH-dependent PL behaviors. Based on the switching between green and blue emission in different pH regions, the xylose-derived CDs solution was demonstrated to be a promising fluorescent ink for anti-counterfeit printing. This research open a door for value-added utilization of xylose, as well as providing a facile and green strategy for large-scale preparation of CDs.
Graphene based sensors have shown excellent potential in the trace detection of specific gases which are hazardous to humans or environmentally toxic. Sensor designs incorporating pristine graphene, graphene oxide, and nano-patterned graphene have been the focus of much recent experimental and computational research. The application of graphene based sensors in the trace detection of explosives has seen relatively limited study, due in part to the difficulties of conducting experiments using the nitramine and aromatic explosives of central interest. Computational studies of explosive sensors are not subject to hazardous materials handling constraints, and may be used to complement experimental research on the development of low weight, low power, graphene based sensors. Ab initio models of five different graphene nanoribbon sensor configurations have been developed, and their chemiresistive response to three widely used explosives and four background gases has been investigated. The results indicate that the sensitivity and selectivity of nanoribbon devices exposed to mixtures of explosives and background gases will vary significantly with explosive type and sensor configuration.
Carbon Dots (CDs) were obtained using a hydrothermal method and used for the detection of fingerprints through fluorescent imaging. Synthesized CDs exhibited a brightness emission at 495 nm, which
was related to their structural and chemical properties. The results of detailed surface characterizations by XPS, ss-NMR and fluorescence spectroscopies, suggested that the negative charge of the functionals groups promoted electrostatic interactions between the charged CDs surface functional groups (amine, amide and carboxylic) and the secretion components present in the thin layer of fluid left on the surface upon its direct contact with human fingers. The obtained results were validated by the scientific protocol
of the Police Automated Fingerprint Identification System (AFIS) based on a biometric identification.
Detection of explosive residues in soil and post-blast debris is an important issue in sensor design for environmental and criminological purposes. An easy-to-use and low-cost gold nanoparticles (AuNPs)-based colorimetric sensor was developed for the determination of nitroaromatic explosives, i.e., trinitrotoluene (TNT) and tetryl, capable of analyte detection at picomolar (pM) levels. The sensor nanoparticles were synthesized by functionalizing the negatively-charged thioglycolic acid (TGA)-modified AuNPs with positively-charged (±)-trans-1,2-diaminocyclohexane (DACH) at a carefully calculated pH. The working principle of the sensor is charge-transfer (CT) interaction between the electron-rich free amino (–NH2) group of DACH and the electron-deficient –NO2 groups of TNT/tetryl, added to possible nanoparticle agglomerization via electrostatic interaction of TNT-Meisenheimer anions with more than one cationic DACH-modified AuNPs. The limit of detection (LOD) and limit of quantification (LOQ) of the sensor were 1.76 pM and 5.87 pM for TNT, and 1.74 pM and 5.80 pM for tetryl, respectively. TNT, tetryl and tetrytol, extracted from nitroaromatic explosive‒contaminated soil sample, were determined with the proposed sensor, yielding good recoveries. The sensor could be selectively applied to various mixtures of TNT with common energetic materials such as RDX, HMX, PETN. Additionally, common soil ions (Cl⁻, NO3⁻, SO4²⁻, K⁺, Mg²⁺, Ca²⁺, Cu²⁺, Fe²⁺, Fe³⁺ and Al³⁺) as well as detergents, sugar, sweeteners, acetylsalicylic acid (aspirin), caffeine and paracetamol-based painkiller drugs, which may be used as camouflage materials for explosives, either had no adverse effects or removable interferences on the detection method. The developed method was statistically validated against a GC–MS literature method.
Boron-doped multi-walled carbon nanotubes (B-MWCNTs) were synthesized, treated with hydrochloric acid, “piranha” solution, and decorated with gold nanoparticles (AuNPs). B-MWCNTs were characterized using Raman spectroscopy, scanning electron- and transmission electron microscopy, and electrochemical techniques. The results exhibit enhanced response and sensitivity of B-MWCNTs upon modification with AuNPs. Analysis of dopamine (DA) and epinephrine (EP) in presence of uric acid (UA) was investigated on B-MWCNTs/AuNPs in pig blood serum. Limits of detection of 0.20 and 0.30 μM were estimated for DA and EP, respectively. The findings demonstrate that B-MWCNTs/AuNPs is proper for analysis of DA and EP under coexistence of UA.
The development of base pair selective fluorescent binding probes and their interaction mode with nucleic acids have created great interest for sensing and biomedical applications. Herein, we have used chicken egg shell membrane (ESM) as a cost effective easily available protein source for the synthesis of highly fluorescent carbon dots. The detailed characterizations have confirmed the in situ formation of heteroatom doped graphitic carbon nanodots (CDs) from ESM. The intrinsic fluorescence property of the material has been utilized for the label free binding of duplex deoxyribonucleic acid (DNA). The interaction of different natural and synthetic DNAs with carbon dots resulted in the enhancement of fluorescence characteristics of the latter. Analysis of the binding data obtained from steady state fluorescence studies revealed a selective and stronger affinity of CDs to the adenine–thymine (AT) base pair rich double stranded DNA (ds DNA) than that of the guanine–cytosine (GC) pair rich ds DNA. Base pair specific binding was further validated from isothermal titration calorimetry (ITC) and melting temperature data. The thermodynamic profile revealed endothermic binding that was driven by the hydrophobic interaction at the nano–bio interfaces. The results reveal the potential of carbon dots as a new and promising fluorescent probe for base pair selective and sequence specific DNA recognition.
Latent fingerprints (LFPs) imaging is the most important approach to identify individuals, and there is a persisting need for the development of simple, rapid, accurate, and universal LFPs recognition methods. The nitrogen- and sulfur-doped solid fluorescent carbon dots (N,S-SFCD) are synthesized with a simple microwave-assisted method by using l-glutathione and citric acid as precursors. The obtained N,S-SFCD has a uniform size from 2 to 7 nm with quantum yield over 48%. The presence of heteroatoms and functional groups on the surface endows the N,S-SFCD with good dispersibility and strong fluorescence emission, and overcomes the typical aggregation-induced fluorescence quenching, thus allowing the N,S-SFCD to be used in both solution and their powder forms. Furthermore, the color-tunable fluorescence, electrostatic interaction with fingerprints, and good stability enable N, S-SFCD to act as an excellent chemosensor for fluorescence imaging. LFPs are detected with high resolution through powder method, and their second- and third-level substructures are clearly identified. The method is validated for LFPs visualization on various substrates, and aged (7, 15, and 30 d) LFPs can also be successfully stained with N,S-SFCD. The results demonstrate that the N,S-SFCD as a developer has great potential in LFPs imaging for forensic investigations.
The surface functionalization of carbon dots (CDs) can introduce an additional dimension for the control of their photoluminescence properties and effective promotion of the applications of CDs such as imaging, sensing, etc. In this study, a simple one-step carbonization using Tween 80 as the sole carbon source is described for directly synthesizing white-emitting CDs (WCDs) in high yield. The results revealed the presence of several long alkyl chains on the surface of the as-fabricated WCDs, which effectively suppress the aggregation-caused quenching (ACQ) effect and emit bright white luminescence under an UV illumination of 365 nm in the solution and solid states. Besides, together with the surface protection of long alkyl chains, WCDs preferentially interact with lipophilic fatty residues and are beneficial for the label-free imaging of latent fingerprints. This study provides a promising new method to not only effectively inhibit the intrinsic ACQ effect of CDs but also develop the surface engineering of functionalized white-emitting CDs for practical applications via facile synthesis.
Generally, carbon nanoparticles with a size of 10 nm (or less) are called carbon quantum dots (CQDs, C-dots or CD), which have created huge excitement due to their advantages in chemical inertness, high water solubility, excellent biocompatibility, resistance to photobleaching and various optical superiority. In this article, we describe the recent advancements in the area of CQDs; concentrating on their synthesis techniques, size control, surface modification approaches, optical properties, luminescent mechanism, and their applications in bioimaging, biosensing, drug delivery and catalysis.
Brightly red fluorescent carbon dots are synthesized hydrothermally and dissolved in diluted hydrochloric acid solution. Such carbon dots exhibit excitation-independent emission at about 620 nm with quantum yield over 10%, which is visible in daylight. After the carbon dots solution is sprayed to the fingerprints on various solid substrates and dried in air, clear fingerprints can be seen under an ultraviolet lamp and stay stable for 1 day. Detailed characterizations suggest that during the drying process, the coffee-ring effect and the electrostatic interactions between the carbon dots and the fingerprint residues prevent the typical aggregation-induced fluorescence quenching of carbon dots.
Fluorescent carbon dots (CDs) are a new class of carbon nanomaterials and have demonstrated excellent optical properties, good biocompatibility, great aqueous solubility, low cost, simple synthesis, etc. Since their discovery, various synthesis methods using different precursors were developed, which were mainly classified as top-down and bottom-up approaches. CDs have presented many applications, and this review article mainly focuses on the development of CDs based fluorescent sensors in recent 5 years. The sensing mechanisms, senor design and sensing properties to various targets are summarized. A broad range of analytes including cations, anions, small molecules, macromolecules, cells and bacteria have been discussed. In addition, the challenges and future directions for CDs as sensing materials are also presented.
Anti-counterfeiting patterns are encrypted with nanotaggants that are selectively excited at distinct wavelengths. Decryption is realized by examining the temporal color or graphic responses of the pattern under various illumination wavelengths. The covert color and graphic codes that are designable through control of the nanotaggant composition are expected to provide high-level security.
Carbon quantum dots (CQDs) as a rising star of carbon nanomaterials, by virtue of their unique physicochemical, optical and electronic properties, have displayed tremendous momentum in numerous fields such as biosensing, bioimaging, drug delivery, optoelectronics, photovoltaics and photocatalysis. In particular, the rich optical and electronic properties of CQDs including efficient light harvesting, tunable photoluminescence (PL), extraordinary up-converted photoluminescence (UCPL) and outstanding photoinduced electron transfer have attracted considerable interest in different photocatalytic applications for the sake of full utilization of the solar spectrum. This review aims to demonstrate the recent progress in the synthesis, properties and photocatalytic applications of CQDs, particularly highlighting the fundamental multifaceted roles of CQDs in photoredox processes. Furthermore, we discuss the challenges and future direction of CQD-based materials in this booming research field, with a perspective toward the ultimate achievement of highly efficient and long-term stable CQD-based photocatalysts.
In recent years, the emerging fluorescent carbon dots have shown enormous potentials for biomedical and optoelectronic applications owing to their outstanding characteristics such as good biocompatibility, low cytotoxicity, photostability and versatility in addition to their unique tunable photoluminescence and other exceptional physicochemical properties. In this review, we will update the latest researches on the synthesis, structure, optical and electronic properties of CDs as well as their advanced applications in biomedicine and optoelectronics. We will mainly discuss the applications of CDs in bioimaging with emphasis on stem cells imaging including normal and cancer stem cells, cell nucleus imaging, two-photon fluorescence imaging, red or near-infrared emission for in vivo imaging, cancer therapy including photodynamic therapy, photothermal therapy and chemotherapy, and optoelectronic applications including light emitting diodes and solar energy conversion. Finally, we will size up current challenges on the research of CDs and project future directions of the field. We hope that this review will provide critical insights to inspire new exciting discoveries on CDs from both fundamental and practical standpoints so that the realization of their potential in the biomedical and optoelectronic areas can be facilitated.
A pyrolysis method for synthesizing carbon nanoparticles (CNPs) were developed by using malic acid and ammonium oxalate as raw materials. The incorporation of a minor amount of carbon nanoparticles into starch powder imparts remarkable color-tunability. Based on this phenomenon, an environment friendly fluorescent starch powder for detecting latent fingerprints in non-porous surfaces was prepared. The fingerprints on different non-porous surfaces developed with this powder showed very good fluorescent images under ultraviolet excitation. The method using fluorescent starch powder as fluorescent marks is simple, rapid and green. Experimental results illustrated the effectiveness of proposed methods, enabling its practical applications in forensic sciences.
Abstract In this work, we report the smart application of AgNPs based sensors for determination of time since death (TSD) via recognition and quantification of vitreous humor (VH) cystine as well as provide the portability for on spot determination of TSD. The lower detection limit was found to be 7.0 ng/ml with prominent selectivity. It was found that there is a linear correlation between the VH cystine concentration and TSD as the concentration of cystine increases up to 96 h±3.9 h. Further for the first time TSD determination is given a smart approach and it proves to have a great utility up to 24 h±2.6 h. The linear regression equation between TSD (the dependent variable), RGB intensity of cystine concentration till 24 h (the independent variable) was found to be TSD=26.69+−0.05*x. The proposed method gives the smart detection, portability, rapidity, sensitivity, selectivity as well as cost effectiveness for determination of time since death.
We have developed a hybrid hydrogel nanocomposite film via conjugation of oxidised carbon dots synthesized from 11-mercaptoundecanoic acid. The potential applicability of the film was then successfully tested for removal of Ca2+ and Mg2+ ions from solution.
Here we first reported an ultrasensitive fluorescence resonance energy transfer (FRET) biosensor of dichlorvos based on carbon dots and the traditionally colorimetric Ellman’s test. In Ellman’s test, the absorption intensity of 5-thio-2-nitrobenzoic acid anion (TNB−) at 412 nm can be used for the determination of acetylcholinesterase (AChE) and its inhibitor. We chose TNB− as energy acceptors to construct a FRET sensing system of AChE and its inhibitor. Quaternized carbon dots (Q-CDs) were chosen as energy donors to form an effective FRET system. By a two-step synthetic method, the Q-CDs with high quantum yield (34.2%) were successfully prepared. Experimental results showed TNB− can quench the fluorescence of Q-CDs to a large extent, which indicated an effective FRET between Q-CDs and TNB− was successfully established. As the inhibitor of AChE and common organophosphorus insecticide, dichlorvos can be detected using this sensing system. Under optimal conditions, the linear range of dichlorvos was 5.0 × 10−11 − 1.0 × 10−7 M. Owing to the high sensitivity and green fluorescent material with high quantum yield, this FRET sensing system was adaptable for automated analyzers using in the rapid determination of a great quantity of samples.
The detection of nitroaromatic explosives is of great importance owing to their strong explosive power and harmfulness in terms of the environment, homeland security and public safety. Herein, rare earth-doped carbon dots with multifunctional features were firstly prepared by simply keeping the mixture of terbium(iii) nitrate pentahydrate and citric acid at 190 °C for 30 min. The as-prepared terbium doped carbon dots (Tb-CDs), through a rapid and simple direct carbonization route, have a size of about 3 nm, and exhibit excitation wavelength dependent emission of blue fluorescence, are stable, and can be applied for the selective and colorimetric detection of 2,4,6-trinitrophenol (TNP) in the range of 500 nM-100 μM with a limit of detection of 200 nM based on the inner filtering effect (IFE) of the excitation and emission bands of Tb-CDs by TNP and the electron transfer (ET) from Tb-CDs to TNP, giving a precise and highly reproducible result for detecting complex water samples.
An ultrafast and facile method for the preparation of fluorescent nitrogen-doped carbon nanoparticles (CNPs) has been developed from a single precursor (ammonium citrate dibasic serving as both carbon and nitrogen sources) using cheap home-use microwave oven. The obtained CNPs showed strong blue fluorescence with a quantum yield of ~ 20% and displayed excitation-independent fluorescence behavior. The effects of preparation conditions on fluorescence behavior of CNPs were systematically investigated, while the as-prepared CNPs were thoroughly characterized using various advanced techniques. The mechanism of nanoparticle formation was also discussed and proposed. Furthermore, it was interestingly found that explosive picric acid (PA) could quench the fluorescence signal of CNPs significantly and selectively, while other nitroaromatic explosives have insignificant effect on its fluorescence intensity. The excellent sensing performance to picric acid could be attributed to the synergistic effect of its low molecular orbitals, the presence of fluorescence resonance energy transfer as well as acid-base interactions between picric acid and fluorescent CNPs. These findings here suggest a simple way to prepare highly fluorescent CNPs, which holds great promise in the development of sensitive and selective sensors for PA detection.
We report a new and facile method for the synthesis of highly fluorescent carbon dots (Cdots) using a commercially available induction coil heater. An aqueous solution of citric acid and a diamine compound was heated at 100 degrees C for 12-15 min, upon which the Cdots were produced. The Cdots, with an average size of less than 5 nm (produced when ethylenediamine was used), emitted a blue light with a high quantum yield when excited under UV light. The quantum yield was dependent on the nature of diamine and was as high as 73.5% for ethylenediamine. The as-prepared Cdots could be easily converted into a gel by mixing with chitosan biopolymer. The gel could be used for filling up the refill of a ball-point pen and can be used for UV-active marking, for sensing of explosive compounds (such as picric acid and 2,4-dinitrophenol) with high efficiency and for other fluorescence based applications. The use of a commercial induction coil heater, scalability and high chance of commercial viability make the method particularly appealing.
The incorporation of a minor amount of carbogenic nanoparticles into powder compositions imparts remarkable colour-tuneability, without compromising the flowability. In a proof-of-concept demonstration we report the use of these hybrid nanopowders for the visual enhancement of latent fingerprints where they effectively resolve issues arising from poor contrast against multi-coloured or patterned backgrounds.
