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Nanostrip Flexible Microwave Enzymatic Biosensor for Noninvasive Epidermal Glucose Sensing
Abstract
Microwave sensors based on microstrip antennas are promising as wearable devices because of their flexibility and wireless communication compatibility. However, their sensitivity is limited due to the reduced sensor size and the potential of biochemical monitoring need to be explored. In this work, we present a new concept to enhance the microwave signals using of nanostrip-based metamaterials. The introduction of the nanostrip structures were achieved by theory and simulations. Experiments proof their enhancement to the electric field and sensing response in the characteristic gigahertz (GHz) wave band. Ordered nanostrips were fabricated on plastic substrate through simple nanoscale printing approach. Glucose oxidase is directly doped into the nanostrips, which enables a flexible wearable enzymatic biosensor for glucose sensing. Sensing experiments demonstrated that the nanostrip biosensor gives excellent performance for glucose detection, including high sensitivity, fast response, low detection limit, high affinity, and low power consumption. The applicability of the nanostrip-based sensor as wearable epidermal device for real-time noninvasive monitoring of glucose in sweat is verified as well.
... Up to now, epidermal sensors towards the health monitoring are based on various materials including polymers, hydrogels, different nanomaterials, and the combination of these materials are capable of the detection of the physical parameters e.g., Fig. 3. (i) Schematic illustration showing the epidermal patch, ISF extraction mechanism, and glucose detection mechanisms, and the great correlation between the ISF glucose level as well as the blood glucose concentration [59]. (ii) Schematic representations illustrating the structure of the sensor and the sensing mechanism [63]. (iii) (a) Schematic illustration showing the iontophoresis printable electrodes. ...
... One-dimensional materials including nanowires, nanofibers, and nanostrips are optimal materials for epidermal sensors due to their high surface-to-volume ratio and thus prominent sensing ability [61,62]. Xue et al. reported a microwave epidermal glucose sensor based on a nanostrip structure [63]. The nanostrip consists of polymer (PEDOT: PSS) nanowire and gold antenna and was deposited on a plastic substrate by a simple nanoscale printing approach (Fig. 3(ii)). ...
The epidermal sensor, a kind of wearable epidermal electronics, has become one of the rising research fields with vast applications because they are wireless, lighter, more flexible, compatible with human skin compared with conventional wearable sensors. A large number of physical and biochemical parameters of the human body, human motion, gases can be continuously sensed by epidermal sensors to real-time monitor human health and sports as well as the atmosphere in various environments. In this review, the state-of-the-art materials, e.g., one-dimensional (1D) nanomaterials, two-dimensional (2D) nanosheets, polymers thin film, and hydrogels applied in the epidermal sensors are discussed, and the practical applications are divided into three subtopics of epidermal sensors towards health monitoring, motion monitoring as well as gas monitoring and a prospective of applications of epidermal sensors is also discussed.
... Compared to traditional glucose sensors, flexible wearable devices have emerged as highly promising tools for in situ biomarker analysis in body fluids, such as sweat and interstitial fluids, providing a means to monitor blood glucose levels [169]. Sweat glucose has shown a qualitative correlation with blood glucose levels [170], and the integration of flexible electrodes with printed circuit boards (PCBs) has enabled the development of complete wearable devices. ...
Metal–organic frameworks (MOFs), constructed by coordination between metal-containing nodes and organic linkers, are widely used in various fields due to the advantages of tunable pores, diverse functional sites, stable structure, and multi-functionality. It should be noted that MOF-based materials play a major role in glucose detection, serving as a signal transducer or functional substrate for embedding nanoparticles/enzymes. Diabetes is one of the most common and fast-growing diseases worldwide, whose main clinical manifestation is high blood sugar levels. Therefore, accurate, sensitive, and point-of-care glucose detection is necessary. This review orderly introduces general synthetic strategies of MOF-based materials (pristine MOF, nanoparticles, or enzymes-modified MOF and MOF-derived materials) and detection methods (electrochemical and optical methods) for glucose detection. Then, the review refers to the novel MOF-based glucose detection devices (flexible wearable devices and microfluidic chips), which enable non-invasive continuous glucose monitoring or low-cost microscale detection. On the basis of describing the development of glucose sensors based on MOF materials in the past five years, the review presents merits, demerits, and possible improvements of various detection methods.
... Electrochemical biosensors are the most commonly used methods for sweat biomarker detection (glucose, lactate, cortisol, cytokines, nutrients, etc.) where analytes are converted into electrical signals by functionalized electrodes and then transmitted to the processing components [38,40,80,104,112,113]. Based on the different mechanisms of detecting electrodes and identifying the analytes, the electrochemical biosensors can be categorized into three main types, including enzyme-based [80,[114][115][116], immune-based [92,101,117], and aptamer-based biosensors [37,118,119]. ...
Biological information detection technology is mainly used for the detection of physiological and biochemical parameters closely related to human tissues and organ lesions, such as biomarkers. This technology has important value in the clinical diagnosis and treatment of chronic diseases in their early stages. Wearable biosensors can be integrated with the Internet of Things and Big Data to realize the detection, transmission, storage, and comprehensive analysis of human physiological and biochemical information. This technology has extremely wide applications and considerable market prospects in frontier fields including personal health monitoring, chronic disease diagnosis and management, and home medical care. In this review, we systematically summarized the sweat biomarkers, introduced the sweat extraction and collection methods, and discussed the application and development of epidermal wearable biosensors for monitoring biomarkers in sweat in preclinical research in recent years. In addition, the current challenges and development prospects in this field were discussed.
... where α refers to the charge transfer coefficient, υ (V⋅s -1 ) is the scan rate, R= 8.314 J⋅K -1 ⋅mol -1 , T = 298 K, and F= 96,485 C⋅mol -1 . During the detection process, GOx catalyzed the oxidation of glucose by oxygen to generate gluconolactone and hydrogen peroxide (H 2 O 2 ) [35,36]. The CV response curves of GOx/AuNPs/TA-APTES/aCC sensor in nitrogen (N 2 )-saturated, air-saturated, and oxygen (O 2 )-saturated PBS buffer (0.1 M, pH 6.0) containing 1 mM glucose are gathered in Fig. 4c. ...
... Nevertheless, more recently, scientists have also turned their interest to sweat sampling and wearable sensors, not only for GLU but for other biomarkers too, thanks to the ease of sampling from the skin surface, as the GLU blood levels are associated with the sweat levels [4][5][6]. GLU sensors are divided into enzymatic and non-enzymatic ones, with the first ones being based on the presence of enzymes such as GLU oxidase, hexokinase, and GLU dehydrogenase [1,7]. On the other hand, non-enzymatic sensors are broadly adaptable, providing stability, simplicity, and reproducibility, while are not affected by temperature, pH, or humidity [8][9][10]. ...
In an attempt to expand the coordination chemistry of N,N’-bis(2,4-dicarboxyphenyl)-oxalamide (H6L) ligand, we isolated and structurally characterized two new Fe(II) Metal-Organic Frameworks (MOFs), namely [Fe2(H2L)(H2O)5] (3D-Fe-MOF) and [Fe(H4L)(H2O)2]∙2H2O, (2D-Fe-MOF) by carefully adjusting the reaction conditions to achieve the optimal degree of deprotonation of the bridging ligand. Both MOFs were found stable in water, as evidenced by powder X-ray diffraction data and their ability to sorb glucose (GLU) from either an aqueous solution or artificial sweat was investigated only to show negligible sorption. Α graphite paste sensor (GPE) using the 3D-Fe-MOF as a modifier was fabricated. Τhe 3D-Fe-MOF modified GPE was assessed for non-enzymatic GLU detection in aqueous solution at pH 6 via differential pulse voltammetry and the preliminary results were discussed.
... Wearable sensors interface with the physiological samples via the skin, where they collect and examine sweat, saliva and other physiologically relevant fluids in real-time and relay the collected information (Heikenfeld et al., 2018;Khan et al., 2019). Commercial and lab-scale wearable sensors are available in the form of patches or tattoo (Cui et al., 2020;, bandages (Heikenfeld et al., 2018;Xue et al., 2020), wrist bands (Promphet et al., 2020;Zhao et al., 2019), gloves (Luo et al., 2018), clothing material (Promphet et al., 2020), mouth guard and contact lens (Tseng et al., 2018). Multiplexing of these devices with enzymes allow the use of inherent selectivity and optimum activity under mild physiological condition of pH and temperature. ...
The rapidly growing electronic and plastic wastes has become a global environmental concern. Developing advanced and environmentally safe agro-based materials is an emerging field with an enormous potential for applications in sensors and devices. Here, an agro-based material as membrane has been developed by incorporating tapioca starch and banana peel powder in polylactic acid, with uniform dispersibility and amorphous nature. The material was used for the development of electrochemical sensor for S-gene of SARS-CoV-2. Further, the membrane was used for the development of a non-invasive skin patch for the detection of glucose and a sensor for the assessment of fruit juice quality. Using OECD-recommended model systems, the developed membrane was found to be non-toxic towards aquatic and terrestrial non-target organisms. The developed conductive material opens new avenues in various electrochemical, analytical, and biological applications.
... Baghelani et al. evaluated the performance of a tag split-ring resonator using ISF solutions that were simulated in a detection range of 36-450 mg dl À1 and a detection limit of 0.01 mg dl À1 at the operating frequency of 4 GHz [70]. On the other hand, Xue et al. developed a microwave biosensor based on nanostrips for non-invasive glucose detection through sweat [71]. The sensor was built using microwave sensors with microstrip antennas to improve sensitivity, and GOx was immobilised on nanostrips to improve performance. ...
Monitoring blood glucose levels is a vital indicator of diabetes mellitus management. The mainstream techniques of glucometers are invasive, painful, expensive, intermittent, and time-consuming. The ever-increasing number of global diabetic patients urges the development of alternative non-invasive glucose monitoring techniques. Recent advances in electrochemical biosensors, biomaterials, wearable sensors, biomedical signal processing, and microfabrication technologies have led to significant research and ideas in elevating the patient's life quality. This review provides up-to-date information about the available technologies and compares the advantages and limitations of invasive and non-invasive monitoring techniques. The scope of measuring glucose concentration in other bio-fluids such as interstitial fluid (ISF), tears, saliva, and sweat are also discussed. The high accuracy level of invasive methods in measuring blood glucose concentrations gives them superiority over other methods due to lower average absolute error between the detected glucose concentration and reference values. Whereas minimally invasive, and non-invasive techniques have the advantages of continuous and pain-free monitoring. Various blood glucose monitoring techniques have been evaluated based on their correlation to blood, patient-friendly, time efficiency, cost efficiency, and accuracy. Finally, this review also compares the currently available glucose monitoring devices in the market.
... Wearable biosensors have become futuristic devices as they are widely used to monitor personal and public health and are widely recommended by health experts and physicians. Today, various types of biosensors are available in the market which is used to monitor heart rate, sleep time, temperature, stress management, oxygen level, steps, voice, breath, motion, humidity, pressure, force, voice, etc. Heikenfeld et al., 2018Heikenfeld et al., , 2019Lou et al., 2017;Xue et al., 2020). However, its potentiality and affordability for every person is still a challenge to achieve, but an increase in the research is bringing us near towards future revolution in the biomedical field, practices, and healthcare facilities. ...
An individual's health is one of the essential aspects of life, but due to the limited technology at health care centers, many people face various restrictions during their treatment. These days, Internet-of-Things (IoT) is the most fascinating topic that provides solutions to these limitations in various ways. The IoT is utilized in various healthcare conducts that include detection, treatment, and monitoring of diseases. Wearable devices are a part of IoT that is proposed for helping patients to get the correct treatment. The conventional communication networks developed for humans-based applications face many issues like stringent latency, restricted computing capability, and short battery life. On the other hand, the onset of 5G has developed a new set of technologies that offer the vital "backbone” for connecting to the billions of devices for the upcoming IoT that would completely modify our professional and private lives. Due to the data capabilities, intelligent management, and superfast connectivity of 5G, this network has enabled new health care opportunities that include treatment, data analytics, diagnostics, and imaging. In the current review, a systematic literature survey of IoT, IoT-based wearable devices, and the role of 5G in IoT for healthcare is described in detail. Furthermore, we have explained the usage of wearable devices in detecting the issue in terms of healthcare, such as curing, monitoring, and detection of disease. Nevertheless, this review article also emphasizes the employment of IoT architecture and its wearable devices in addition to the upcoming research challenges related to this area.
... Integration with a nano strip antenna was proposed in this study to enhance the microwave signals, in turn improving the sensitivity of the sensor. A linear response for glucose concentration was recorded in the range 0.1 nM to 10 mM with sensitivity of 0.026 dB/log (nM) [111]. Dautta et al. developed a wireless stretchable and scalable phenylboronic acid-based biosensor for glucose detection in sweat with a hydrogel-interlayer radiofrequency (RF) resonator. ...
Biosensors have potentially revolutionized the biomedical field. Their portability, cost-effectiveness, and ease of operation have made the market for these biosensors to grow rapidly. Diabetes mellitus is the condition of having high glucose content in the body, and it has become one of the very common conditions that is leading to deaths worldwide. Although it still has no cure or prevention, if monitored and treated with appropriate medication, the complications can be hindered and mitigated. Glucose content in the body can be detected using various biological fluids, namely blood, sweat, urine, interstitial fluids, tears, breath, and saliva. In the past decade, there has been an influx of potential biosensor technologies for continuous glucose level estimation. This literature review provides a comprehensive update on the recent advances in the field of biofluid-based sensors for glucose level detection in terms of methods, methodology and materials used.
... Indeed, when the temperature exceeds the typical VPTT, the polymer network shrinks, and the water contained in the hydrogel is expelled from the structure 36 . Thus, crosslinked thermoresponsive hydrogels reversibly switch from a hydrophilic, swollen state to a hydrophobic, shrunken state when heated above the volume phase transition temperature 37 . ...
One of the most fascinating areas in the field of smart biopolymers is biomolecule sensing. Accordingly, multifunctional biomimetic, biocompatible, and stimuli-responsive materials based on hydrogels have attracted much interest. Within this framework, the design of nanostructured materials that do not require any external energy source is beneficial for developing a platform for sensing glucose in body fluids. In this article, we report the realization and application of an innovative platform consisting of two outer layers of a nanocomposite plasmonic hydrogel plus one inner layer of electrospun mat fabricated by electrospinning, where the outer layers exploit photoinitiated free radical polymerization, obtaining a compact and stable device. Inspired by the exceptional features of chameleon skin, plasmonic silver nanocubes are embedded into a poly(N-isopropylacrylamide)-based hydrogel network to obtain enhanced thermoresponsive and antibacterial properties. The introduction of an electrospun mat creates a compatible environment for the homogeneous hydrogel coating while imparting excellent mechanical and structural properties to the final system. Chemical, morphological, and optical characterizations were performed to investigate the structure of the layers and the multifunctional platform. The synergetic effect of the nanostructured system’s photothermal responsivity and antibacterial properties was evaluated. The sensing features associated with the optical properties of silver nanocubes revealed that the proposed multifunctional system is a promising candidate for glucose-sensing applications.
... The existence of polymer encapsulation of biomedical sensors, such as polyethylene naphthalene (PEN) [1], polydimethylsiloxane (PDMS) [2], [3], polyethylene terephthalate (PET) [4], epoxy [5] shows that this polymer material was demanded for encapsulation of biomedical fields, mainly for the sensor. For instance, the sensor that used plastic encapsulation, such as temperature sensor, humidity sensor, pressure sensor, flow sensor, acoustic sensor, etc. ...
Oil palm nanocellulose has been demonstrated to display a wide range of unique properties for many fields. They are suitable for biomedical applications and have been used in this domain for decades. The current variety of nanocellulose fibers allows the development of new nanocomposites. This work fabricated oil palm nanocellulose with variations of fiber loading (1, 2, 3, 4, and 5 wt%) and thermoplastic polyurethane (TPU) polymer matrix by using a mechanical stirring followed by hot pressing methods. The physical characters of nanocellulose oil palm reinforced TPU nanocomposites, such as water absorption, thickness swelling, and density were characterized. The fiber loading of oil palm nanocellulose content at 5 wt% shows the highest water uptake, thickness swelling, and the lowest density properties of oil palm nanocellulose reinforced TPU nanocomposites.
... The existence of polymer encapsulation of biomedical sensors, such as polyethylene naphthalene (PEN) [1], polydimethylsiloxane (PDMS) [2], [3], polyethylene terephthalate (PET) [4], epoxy [5] shows that this polymer material was demanded for encapsulation of biomedical fields, mainly for the sensor. For instance, the sensor that used plastic encapsulation, such as temperature sensor, humidity sensor, pressure sensor, flow sensor, acoustic sensor, etc. ...
Oil palm nanocellulose has been demonstrated to display a wide range of unique properties for many fields. They are suitable for biomedical applications and have been used in this domain for decades. The current variety of nanocellulose fibers allows the development of new nanocomposites. This work fabricated oil palm nanocellulose with variations of fiber loading (1, 2, 3, 4, and 5 wt%) and thermoplastic polyurethane (TPU) polymer matrix by using a mechanical stirring followed by hot pressing methods. The physical characters of nanocellulose oil palm reinforced TPU nanocomposites, such as water absorption, thickness swelling, and density were characterized. The fiber loading of oil palm nanocellulose content at 5 wt% shows the highest water uptake, thickness swelling, and the lowest density properties of oil palm nanocellulose reinforced TPU nanocomposites.
... The existence of polymer encapsulation of biomedical sensors, such as polyethylene naphthalene (PEN) [1], polydimethylsiloxane (PDMS) [2], [3], polyethylene terephthalate (PET) [4], epoxy [5] shows that this polymer material was demanded for encapsulation of biomedical fields, mainly for the sensor. For instance, the sensor that used plastic encapsulation, such as temperature sensor, humidity sensor, pressure sensor, flow sensor, acoustic sensor, etc. ...
Oil palm nanocellulose has been demonstrated to display a wide range of unique properties for many fields. They are suitable for biomedical applications and have been used in this domain for decades. The current variety of nanocellulose fibers allows the development of new nanocomposites. This work fabricated oil palm nanocellulose with variations of fiber loading (1, 2, 3, 4, and 5 wt%) and thermoplastic polyurethane (TPU) polymer matrix by using a mechanical stirring followed by hot pressing methods. The physical characters of nanocellulose oil palm reinforced TPU nanocomposites, such as water absorption, thickness swelling, and density were characterized. The fiber loading of oil palm nanocellulose content at 5 wt% shows the highest water uptake, thickness swelling, and the lowest density properties of oil palm nanocellulose reinforced TPU nanocomposites.
... An effective biosensor exhibits several crucial characteristics, namely, high sensitivity, good selectivity, fast response/recovery time, cycle stability, and the capability to operate at low temperatures. In addition to satisfying all of these prerequisites, conductive nanomaterial-based electrodes are renowned for their small size, high surface-to-volume ratio, and unique optical/electrical properties, thereby making them excellent candidates for biosensor-assisted applications [13][14][15][16][17]. ...
Biosensors are of particular importance for the detection of biological analytes at low concentrations. Conducting polymer nanomaterials, which often serve as sensing transducers, are renowned for their small dimensions, high surface-to-volume ratio, and amplified sensitivity. Despite these traits, the widespread implementation of conventional conducting polymer nanomaterials is hampered by their scarcity and lack of structural uniformity. Herein, a brief overview of the latest developments in the synthesis of morphologically tunable conducting polymer-based biosensors is discussed. Research related to the dimensional (0, 1, 2, and 3D) hetero-nanostructures of conducting polymers are highlighted in this paper, and how these structures affect traits such as the speed of charge transfer processes, low-working temperature, high sensitivity and cycle stability are discussed.
... Wearable biosensors have become futuristic devices as they are widely used to monitor personal and public health and are widely recommended by health experts and physicians. Today, various types of biosensors are available in the market which is used to monitor heart rate, sleep time, temperature, stress management, oxygen level, steps, voice, breath, motion, humidity, pressure, force, voice, etc. Heikenfeld et al., 2018Heikenfeld et al., , 2019Lou et al., 2017;Xue et al., 2020). However, its potentiality and affordability for every person is still a challenge to achieve, but an increase in the research is bringing us near towards future revolution in the biomedical field, practices, and healthcare facilities. ...
A microwave biosensor based on a planar low-pass-split ring resonator is proposed for detecting tacrolimus concentrations in solution. The biosensor was used to detect tacrolimus in an aqueous solution and blood samples containing tacrolimus drug concentration. As the concentration of a sample changes, so do its dielectric properties, causing a shift in the resonant frequency and S parameter. The experimental results show that the resonant frequency and insertion loss are highly linearly related to sample concentration for tacrolimus aqueous solution detection (R² = 0.99). The detection results of real blood samples were similar to those of tacrolimus aqueous solution, with a linear relationship using frequency (R² = 0.99) and insertion loss (R² = 0.91),to demonstrate its effectiveness. In addition, the sensor exhibits low limit of detection (LoD) of 0.032 ng/mL. Finally, the frequency detection resolution (FDR) for the concentration variation range of blood samples from tacrolimus is 32.37 MHz/(ng/mL). The higher the FDR value, the higher the sensor's sensitivity to sample concentration detection and resonance frequency variation, demonstrating the feasibility of a label-free biosensing scheme. This study presents simple method for achieving a microwave biosensor that is both highly sensitive and fast response.
We propose a machine learning‐based microwave spectrum detection method based on the nitrogen‐vacancy (NV) color centers in diamonds. The functional relationship between the fluorescence spectrum and standard microwave spectrum was established. The response matrix was calculated using the Tikhonov regularization technique, and an unknown microwave spectrum was reconstructed. Diamond particles with a size of only 5×5 μm2 were placed in the microfluidic structures. Consequently, the frequency detection range of the microwave spectrum ranged from 2.892 to 6.214 GHz with a resolution of 22 kHz. The proposed research opens new paths for microwave spectrum detection and imaging at the microscopic scale. This article is protected by copyright. All rights reserved.
This article presents an approach to significantly improve the resolution of a highly-sensitive microwave planar sensor response with a super-resolution generative adversarial network (SRGAN). Three identical complementary split-ring resonators are coupled so that the sensitivity is doubled. This highly-sensitive resonator with a deep transmission zero at 4.7 GHz is deployed to measure minute variations of glucose in interstitial fluid. Measuring the sensor response with 1001 frequency-points allows differentiating 10 glucose samples within the range of 40–400 mg/dL. However, in practical readout systems with limited number of frequency-points (here 28), recognizing the deep zero in the S21 response lacks precision. Sensor responses (magnitude vs. frequency and phase vs. frequency) are converted into equivalent 2D images (heatmaps: phase vs. frequency with colored pixels as amplitude) to be compatible as SRGAN input. As a result of 8-fold resolution enhancement using SRGAN, the classification accuracy is substantially improved from 62.1% to 93.3%. The proposed passive sensor followed by an SRGAN unit is shown to be practical as a wearable glucose monitoring sensor due to its high-sensitivity and high resolution features in a low-profile design.
Recent advances in nanolithography, miniaturization, and material science, along with developments in wearable electronics, are pushing the frontiers of sensor technology into the large‐scale fabrication of highly sensitive, flexible, stretchable, and multimodal detection systems. Various strategies, including surface engineering, have been developed to control the electrical and mechanical characteristics of sensors. In particular, surface wrinkling provides an effective alternative for improving both the sensing performance and mechanical deformability of flexible and stretchable sensors by releasing interfacial stress, preventing electrical failure, and enlarging surface areas. In this study, recent developments in the fabrication strategies of wrinkling structures for sensor applications are discussed. The fundamental mechanics, geometry control strategies, and various fabricating methods for wrinkling patterns are summarized. Furthermore, the current state of wrinkling approaches and their impacts on the development of various types of sensors, including strain, pressure, temperature, chemical, photodetectors, and multimodal sensors, are reviewed. Finally, existing wrinkling approaches, designs, and sensing strategies are extrapolated into future applications. This review summarizes recent advances in wearable sensors based on surface wrinkling phenomena, which greatly improves the various performances of the device. Basic mechanics, fabrication methods, and various practical applications are extensively discussed. In addition, perspectives for developing wrinkle‐based wearable sensors in the future are suggested.
Against the backdrop of increased public health awareness, inorganic nanomaterials have been widely explored as promising nanoagents for various kinds of biomedical applications. Layered double hydroxides (LDHs), with versatile physicochemical advantages including excellent biocompatibility, pH-sensitive biodegradability, highly tunable chemical composition and structure, and ease of composite formation with other materials, have shown great promise in biomedical applications. In this review, we comprehensively summarize the recent advances in LDH-based nanomaterials for biomedical applications. Firstly, the material categories and advantages of LDH-based nanomaterials are discussed. The preparation and surface modification of LDH-based nanomaterials, including pristine LDHs, LDH-based nanocomposites and LDH-derived nanomaterials, are then described. Thereafter, we systematically describe the great potential of LDHs in biomedical applications including drug/gene delivery, bioimaging diagnosis, cancer therapy, biosensing, tissue engineering, and anti-bacteria. Finally, on the basis of the current state of the art, we conclude with insights on the remaining challenges and future prospects in this rapidly emerging field.
In this work, a new type of graphite paste electrode (GPE) modified with a water-stable Cu(II)-complex is described as new candidate for the voltammetric determination of glucose (GLU) and uric acid (UA) in sweat. The oxidation of CLU and UA was electrocatalyzed by Cu(II) which was electrochemically generated in-situ from the Cu(II)-complex precursor. Three in-house synthesized water-insoluble Cu(II)-complexes {[Cu(PhCOO)(H2O)2]∙PhCOO∙H2O}n, [Cu(Et-saoH)2] and [Cu(Me-saoH)2] (where, Et-saoH2: 2-hydroxypropiophenone oxime, Me-saoH2: 2-hydroxyethanone oxime) were synthesized and compared with conventional copper oxides (CuO and Cu2O) as electrode modifiers for the voltammetric detection of GLU and UA in acidic media. The {[Cu(PhCOO)(H2O)2]∙PhCOO∙H2O}n exhibited the most favorable electrochemical performance and the determination of both biomarkers was carried out without interference from common electroactive metabolites presented in artificial sweat, offering low limits of detection (5 μmol L⁻¹ GLU and 4.6 μmol L⁻¹ UA). The results confirm that {[Cu(PhCOO)(H2O)2]∙PhCOO∙H2O}n-modified GPE is a promising non-enzymatic sensor for the simultaneous determination of GLU and UA in sweat.
Herein, the one-step fabrication of novel three-dimensional sponge-like piezoelectric electrospun nanofiber structures is reported. Ferroelectric polymers are biocompatible and flexible materials that present attractive opportunities for the fabrication of portable energy harvesters for energy efficient wearable electronic devices. While being compatible with diverse fabrication methods, thicker and denser 3D forms have only been obtained from extruder-based, low-yield approaches. Electrospinning polyvinylidene fluoride (PVDF) and polyvinylidene fluoride-co-trifluoroethylene (PVDF-TrFE) solutions with added polyethylene oxide (PEO) and lithium chloride was explored as an alternative approach for the scaled-up fabrication of 3D structures. The resulting PVDF/PEO and PVDF-TrFE/PEO 700 µm thick sponge-like fiber mats were used as active cores for piezoelectric generators. The produced sponge-like core generators achieved an average peak-to-peak voltage of 69.4 V when subjected to a 1.58 N impact force applied at a frequency of 4 Hz and connected to a 15.1 M Ω resistive load. Their measured instantaneous output power of 40.7 µW cm–2 exceeds that of similar state-of-the-art generators by a factor of 2. Our fabrication method provides a low-cost, one-step, and scalable alternative for creating micro- and nanofibrous three-dimensional structures.
Non-enzymatic biosensors based on various nanomaterials with large surface-volume ratios and high catalytic efficiencies have been proposed to compensate for the non-stability and high cost of enzymatic biosensors. However, the construction of a stable, highly sensitive, flexible, three-dimensional (3D), microstructured, non-enzymatic biosensor integrated with a smartphone-based portable system has been challenging. Herein, highly conductive laser-induced graphene (LIG) array with a honeycomb-like 3D microstructure co-decorated with copper(I) oxide and gold nanocatalysts was developed via simple and green electro-deposition and chemical reduction approaches for a miniaturized electrochemical flexible non-enzymatic biosensor. SEM, XRD, Raman and XPS analyzations indicated that the Cu2O and Au nanocatalysts co-decorated three-dimensional, laser-induced graphene hybrid nanomaterials were developed successfully. The signal of the biosensor was improved by more than 10 fold compared to the LIG alone due to the co-decorated with copper(I) oxide and gold nanocatalysts. The fabricated electrochemical biochip was integrated with a smartphone-based microstation for glucose monitoring, presenting a larger linear interval of 1–20 mM with an excellent sensitivity of 236 μA/mM/cm² and a relatively low detection limit of 0.31 μM. Noticeably, the biochip could measure blood sugar on curved surfaces and still deliver stable sensing signals after being bent back-and-forth 25 times. The novel biosensor is a potentially valuable flexible electronic device. The hybrid nanomaterials developed in this work may be applicable to other biosensing, catalytic, and energy devices (supercapacitors and batteries).
Nowadays, wearable biosensors are considered the most recent cutting-edge technology in the field of analytical biochemistry. They have attracted increasing attention due to their promising potential to revolutionize traditional medical diagnostic methods. In this context, we present the recent trends related to the applications of biorecognition elements in wearable electrical, electrochemical, and optical biosensing devices. Indeed, the first section of this chapter deals with the main biorecognition elements employed, and the most used immobilization techniques for the development of wearable biosensors. In the second part, we highlight the different applications of wearable biosensors in body fluids, including saliva, sweat, and tears. Finally, we summarize the current challenges and prospects of the implementation of biorecognition elements in wearable biosensors field.
Wearable sweat sensors combine the benefits of noninvasive sweat sampling and wearable real-time measurement, providing a powerful platform for monitoring a wealth of biochemical components of sweat related to physiological conditions. The recent progress of wearable sweat sensors is attributed to the rapid development of interdisciplinary research among material science, manufacturing technology, and advanced electronics field. This review focuses on the construction of wearable sweat sensors, especially the design of a flexible sensing interface and integrated wearable sweat sensor. In addition, we outline the extensive applications of wearable sweat sensors from healthcare and sports monitoring to biofuel cells. Finally, several issues and opportunities of future wearable sweat sensors are discussed.
As the increasing number of diabetic around the world and the deficiencies of invasive blood glucose detection such as prickly pain and no continuous monitoring. In this paper, an ultra-wide band microwave based technique combined with a cascaded general regression neural network (C-GRNN) was proposed for blood glucose level estimation to achieve noninvasive and intelligent monitoring. Different glucose solutions were tested by using the reported monitoring system, in which C-GRNN was used for intelligent detection and frequency choice. The proposed C-GRNN could reduce the prediction interval from 12.3858 mg/dl to 2.1375 mg/dl compared with conventional GRNN, and the root mean square error (RMSE) reached 2.20 mg/dl. These results showed good estimation performance. We also conducted a continuous-time blood glucose level (BGL) monitoring on volunteer using proposed noninvasive method. The final results showed well accuracy, where the RMSE and mean absolute percentage error (MAPE) were 13.3208 mg/dl and 9.74% respectively.
Microwave-based sensing for tissue analysis is recently gaining interest due to advantages such as non-ionizing radiation and non-invasiveness. We have developed a set of transmission sensors for microwave-based real-time sensing to quantify muscle mass and quality. In connection, we verified the sensors by 3D simulations, tested them in a laboratory on a homogeneous three-layer tissue model, and collected pilot clinical data in 20 patients and 25 healthy volunteers. This report focuses on initial sensor designs for the Muscle Analyzer System (MAS), their simulation, laboratory trials and clinical trials followed by developing three new sensors and their performance comparison. In the clinical studies, correlation studies were done to compare MAS performance with other clinical standards, specifically the skeletal muscle index, for muscle mass quantification. The results showed limited signal penetration depth for the Split Ring Resonator (SRR) sensor. New sensors were designed incorporating Substrate Integrated Waveguides (SIW) and a bandstop filter to overcome this problem. The sensors were validated through 3D simulations in which they showed increased penetration depth through tissue when compared to the SRR. The second-generation sensors offer higher penetration depth which will improve clinical data collection and validation. The bandstop filter is fabricated and studied in a group of volunteers, showing more reliable data that warrants further continuation of this development.
The COVID‐19 pandemic has continued to spread rapidly, and patients with diabetes are at risk of experiencing rapid progression and poor prognosis for appropriate treatment. Continuous glucose monitoring (CGM), which includes accurately tracking fluctuations in glucose levels without raising the risk of coronavirus exposure, becomes an important strategy for the self‐management of diabetes during this pandemic, efficiently contributing to the diabetes care and the fight against COVID‐19. Despite being less accurate than direct blood glucose monitoring, wearable noninvasive systems can encourage patient adherence by guaranteeing reliable results through high correlation between blood glucose levels and glucose concentrations in various other biofluids. This review highlights the trending technologies of glucose sensors during the ongoing COVID‐19 pandemic (2019–2020) that have been developed to make a significant contribution to effective management of diabetes and prevention of coronavirus spread, from off‐body systems to wearable on‐body CGM devices, including nanostructure and sensor performance in various biofluids. The advantages and disadvantages of various human biofluids for use in glucose sensors are also discussed. Furthermore, the challenges faced by wearable CGM sensors with respect to personalized healthcare during and after the pandemic are deliberated to emphasize the potential future directions of CGM devices for diabetes management.
For decades, diabetes mellitus has been of wide concern with its high global prevalence, resulting in increasing social and financial burdens for individuals, clinical systems and governments. Continuous glucose monitoring (CGM) has become a popular alternative to the portable finger-prick glucometers available in the market for the convenience of diabetic patients. Hence, it has attracted much interest in various glucose sensing technologies to develop novel glucose sensors with better performance and longer lifetime, especially non-invasive or minimally invasive glucose sensing. Effort has also been put into finding biocompatible materials for implantable applications to achieve effective in vivo CGM. Here, we review the state-of-the-art researches in the field of CGM. The currently commercially available CGM technologies have been analyzed and a summary is provided of the potential types of recently researched non-invasive glucose monitors. Furthermore, the challenges and advances towards implantable applications have also been introduced and discussed, especially the novel biocompatible hydrogel aimed at minimizing the adverse impact from foreign-body response. In addition, a large variety of promising glucose-sensing technologies under research have been reviewed, from traditional electrochemical-based glucose sensors to novel optical and other electrical glucose sensors. The recent development and achievement of the reviewed glucose sensing technologies are discussed, together with the market analysis in terms of the statistical data for the newly published patents in the related field. Thus, the promising direction for future work in this field could be concluded.
Nowadays, there is increased demand for wearable sensors for sweat glucose monitoring in order to facilitate diabetes management in a patient-friendly and noninvasive manner. This work describes a wearable glucose monitoring device in the form of an electrochemical ring (e-ring) fabricated by 3D printing. The 3D-printed e-ring consists of three carbon-based plastic electrodes (fabricated using a conductive filament) integrated at the inner side of a ring-shaped flexible plastic holder (fabricated using a nonconductive filament). The e-ring is modified with an electrodeposited gold film and is coupled to a miniature potentiostat directly addressable by a smartphone, offering the possibility for nonenzymatic amperometric self-testing of glucose levels in human sweat. Optical and electrochemical techniques are employed for the characterization of the e-ring. The device is resistant to mechanical bending and enables noninvasive glucose detection in sweat in the physiologically relevant concentration range of 12.5–400 μmol L–1 without interference from common electroactive metabolites. The 3D-printed e-ring bridges the gap between the existing fabrication/sensing technologies and the desired operational features for glucose self-monitoring and may be employed as a paradigm of in-house fabricated wearable sensors.
Conducting polymer composites (CPCs) have been versatily utilized in actualizing advanced devices such as supercapacitors, biosensors, photovoltaic cells, batteries, catalysts, chemical sensors, and so on. Conducting polymer nanocomposites (CPNCs) are derived from hybridization of intrinsically conductive polymers (CPs) with inorganic entities thereby fabricating multifunctional materials with enhanced performances. Conducting polymer bionanocomposites (CPBs) are electrically conducting biocomposites derived from mixing of CPs with biopolymers such as proteins, cellulose, guar-gums, chitosan, chitin, gelatin, and so on, resulting in emancipation of CBs for use in biomedical, agricultural and food engineering due to attainment of biocompatibility, biodegradability, and electrical conductivity. Therefore, this paper presents recently emerging trends in synthesis, characterization, and properties of CP composites, nanocomposites, bionanocomposites, and applications.
The metabolic disorder of glucose in human body will cause diseases such as diabetes and hyperglycemia. Hence the determination of glucose content is very important in clinic diagnosing. In recent years, researchers have proposed various non-invasive wearable sensors for rapid and real-time glucose monitoring from human body fluids. Unlike those reviews which discussed performances, detection environments or substrates of the wearable glucose sensor, this review focuses on the sensing nanomaterials since they are the key elements of most wearable glucose sensors. The sensing nanomaterials such as carbon, metals, and conductive polymers are summarized in detail. And also the structural characteristics of different sensing nanomaterials and the corresponding wearable glucose sensors are highlighted. Finally, we prospect the future development requirements of sensing nanomaterials for wearable glucose sensors. This review would give some insights to the further development of wearable glucose sensors and the modern medical treatment.
Layered nanostructures (LNs), including two-dimensional nanosheets, nanoflakes, and planar nanodots, show large surface-to-volume ratios, unique optical properties, and desired interfacial activities. LNs are highly promising as alternative probes and platforms due to numerous merits, e.g. signal amplification, improved recognition ability, and anti-interference capacity, for emerging sensing applications. Significantly, when stimuli-responsive aggregation occurs, the modified LNs show engineered morphologies, attractive optical absorption and fluorescence characteristics, which are remarkably programmable. On the basis of the altered aggregation behaviours of LNs, as well as their modulated physical and chemical characteristics, a series of novel sensing assays exhibiting enhanced sensitivity, simple operation, multiple functions, and improved anti-interference capacity are reported, contributing to both point-of-care testing and high-throughput measurements. Herein, the aggregation-induced response sensing strategies of LNs are comprehensively summarized with the classification of materials and variation of aggregated routes aiming at understanding dimension-dependent features, expanding nanoscale biosensor applications, and addressing key issues in disease diagnosis and environmental analysis.
Small-sized, low-cost, and high-sensitivity sensors are required for pressure-sensing applications because of their critical role in consumer electronics, automotive applications, and industrial environments. Thus, micro/nanoscale pressure sensors based on micro/nanofabrication and micro/nanoelectromechanical system technologies have emerged as a promising class of pressure sensors on account of their remarkable miniaturization and performance. These sensors have recently been developed to feature multifunctionality and applicability to novel scenarios, such as smart wearable devices and health monitoring systems. In this review, we summarize the major sensing principles used in micro/nanoscale pressure sensors and discuss recent progress in the development of four major categories of these sensors, namely, novel material-based, flexible, implantable, and self-powered pressure sensors. Keywords: M/NEMS, Pressure sensor, Flexible sensor, Piezoresistive sensor, Capacitive sensor, Piezoelectric sensor, Resonant sensor, 2D material
Development of reliable glucose sensors for noninvasive monitoring without interruption or limiting users' mobility is highly desirable, especially for diabetes diagnostics, which requires routine/long‐term monitoring. However, their applications are largely limited by the relatively poor stability. Herein, a porous membrane is synthesized for effective enzyme immobilization and it is robustly anchored to the modified nanotextured electrode solid contacts, so as to realize glucose sensors with significantly enhanced sensing stability and mechanical robustness. To the best of our knowledge, this is the first report of utilizing such nanoporous membranes for electrochemical sensor applications, which eliminates enzyme escape and provides a sufficient surface area for molecular/ion diffusion and interactions, thus ensuring the sustainable catalytic activities of the sensors and generating reliable measureable signals during noninvasive monitoring. The as‐assembled nanostructured glucose sensors demonstrate reliable long‐term stable monitoring with a minimal response drift for up to 20 h, which delivers a remarkable enhancement. Moreover, they can be integrated into a microfluidic sensing patch for noninvasive sweat glucose monitoring. The as‐synthesized nanostructured glucose sensors with remarkable stability can inspire developments of various enzymatic biosensors for reliable noninvasive composition analysis and their ultimate applications in predictive clinical diagnostics, personalized health‐care monitoring, and chronic diseases management. A porous membrane is synthesized for effective enzyme immobilization and to ensure the sustainable catalytic activities of the electrochemical sensors. It is robustly anchored to the modified nanotextured electrode solid contacts to realize glucose sweat sensors with significantly enhanced sensing stability and mechanical robustness, which are highly desirable for applications in noninvasive health monitoring.
This paper describes a low-cost, small size, and high-sensitivity microwave sensor using a Complementary Circular Spiral Resonator (CCSR), which operates at around 2.4 GHz, for identifying liquid samples and determining their dielectric constants. The proposed sensor was fabricated and tested to effectively identify different liquids commonly used in daily life and determine the concentrations of various ethanol–water mixtures at by measuring the resonant frequency of the CCSR. Using acrylic paint, a square channel was drawn at the most sensitive position of the microwave sensor to ensure accuracy of the experiment. To estimate the dielectric constants of the liquids under test, an approximate model was established using a High-Frequency Simulator Structure (HFSS). The results obtained agree very well with the existing data. Two parabolic equations were calculated and fitted to identify unknown liquids and determine the concentrations of ethanol–water mixtures. Thus, our microwave sensor provides a method with high sensitivity and low consumption of material for liquid monitoring and determination, which proves the feasibility and broad prospect of this low-cost system in industrial application.
Flexible and wearable electronics are attracting wide attention due to their potential applications in wearable human health monitoring and care systems. Carbon materials have combined superiorities such as good electrical conductivity, intrinsic and structural flexibility, light weight, high chemical and thermal stability, ease of chemical functionalization, as well as potential mass production, enabling them to be promising candidate materials for flexible and wearable electronics. Consequently, great efforts are devoted to the controlled fabrication of carbon materials with rationally designed structures for applications in next‐generation electronics. Herein, the latest advances in the rational design and controlled fabrication of carbon materials toward applications in flexible and wearable electronics are reviewed. Various carbon materials (carbon nanotubes, graphene, natural‐biomaterial‐derived carbon, etc.) with controlled micro/nanostructures and designed macroscopic morphologies for high‐performance flexible electronics are introduced. The fabrication strategies, working mechanism, performance, and applications of carbon‐based flexible devices are reviewed and discussed, including strain/pressure sensors, temperature/humidity sensors, electrochemical sensors, flexible conductive electrodes/wires, and flexible power devices. Furthermore, the integration of multiple devices toward multifunctional wearable systems is briefly reviewed. Finally, the existing challenges and future opportunities in this field are summarized.
In this work, we propose a metamaterial absorber at microwave frequencies with significant sensitivity and non-destructive sensing capability for grain samples. This absorber is composed of cross-resonators periodically arranged on an ultrathin substrate, a sensing layer filled with grain samples, and a metal ground. The cross-resonator array is fabricated using the printed circuit board process on an FR-4 board. The performance of the proposed metamaterial is demonstrated with both full-wave simulation and measurement results, and the working mechanism is revealed through multi-reflection interference theory. It can serve as a non-contact sensor for food quality control such as adulteration, variety, etc. by detecting shifts in the resonant frequencies. As a direct application, it is shown that the resonant frequency displays a significant blue shift from 7.11 GHz to 7.52 GHz when the mass fraction of stale rice in the mixture of fresh and stale rice is changed from 0% to 100%. In addition, the absorber shows a distinct difference in the resonant absorption frequency for different varieties of grain, which also makes it a candidate for a grain classification sensor. The presented scheme could open up opportunities for microwave metamaterial absorbers to be applied as efficient sensors in the non-destructive evaluation of agricultural and food product quality.
Goal:
This paper reports the use of a novel electromagnetic sensor technique for real-time non-invasive monitoring of blood lactate in human subjects.
Methods:
The technique was demonstrated on 34 participants who undertook a cycling regime, with rest period before and after, to produce a rising and falling lactate response curve. Sensors attached to the arm and legs of participants gathered spectral data, blood samples were measured using a Lactate Pro V2, as well as temperature and heart rate data were collected.
Results:
Pairwise mutual information and neural networks are used to produce a predictive model. The model shows a good correlation (R = 0.78) between the standard invasive and novel non-invasive electromagnetic wave based blood lactate measurements, with an error of 13.4% in the range of 0 - 12 mmol/L.
Conclusion:
The work demonstrates that electromagnetic wave sensors are capable of determining blood lactate level without the need for invasive blood sampling.
Significance:
Measurement of blood metabolites, such as blood lactate, in real-time and non-invasively in hospital environments will reduce the risk of infection, increase the frequency of measurement and ensure timely intervention only when necessary. In sports situations, such tools will enhance training of athletes, and enable more effecting training regimes to be prescribed.
Melamine sponge, also named as nano-sponge, is widely used as abrasive cleaner in our daily life. In this work, the fabrication of wearable strain sensor for human motion detection is first demonstrated with commercial available nano-sponge as starting material. The key resistance sensitive material in the wearable strain sensor is obtained by encapsulation of carbonized nano-sponge (CNS) with silicone resin. The as-fabricated CNS/silicone sensor is highly sensitive to strain with a maximum gauge factor of 18.42. In addition, the CNS/silicone sensor exhibits fast and reliable response to various cyclic loading within a strain range of 0-15% and a loading frequency range of 0.01-1 Hz. Finally, the CNS/silicone sensor as wearable device for human motion detection including joint motion, eye blinking, blood pulse and breathing is demonstrated by attaching the sensor to corresponding part of human body. In consideration of the simple fabrication technique, low material cost and excellent strain sensing performance, the CNS/silicone sensor is believed to have great potential in the next-generation of wearable devices for human motion detection.
We report an ultra-thin electronic decal that can simultaneously collect, transmit and interrogate a bio-fluid. The described technology effectively integrates a thin-film organic electrochemical transistor (sensing component) with an ultrathin microbial nanocellulose wicking membrane (sample handling component). As far as we are aware, OECTs have not been integrated in thin, permeable membrane substrates for epidermal electronics. The design of the biocompatible decal allows for the physical isolation of the electronics from the human body while enabling efficient bio-fluid delivery to the transistor via vertical wicking. High currents and ON-OFF ratios were achieved, with sensitivity as low as 1 mg·L⁻¹.
Gait analysis is an important medical diagnostic process and has many applications in healthcare, rehabilitation, therapy, and exercise training. However, typical gait analysis has to be performed in a gait laboratory, which is inaccessible for a large population and cannot provide natural gait measures. In this paper, we present a novel sensor device, namely, Smart Insole, to tackle the challenge of efficient gait monitoring in real life. An array of electronic textile (eTextile) based pressure sensors are integrated in the insole to fully measure the plantar pressure. Smart Insole is also equipped with a low-cost inertial measurement unit including a 3-axis accelerometer, a 3-axis gyroscope, and a 3-axis magnetometer to capture the gait characteristics in motion. Smart Insole can offer precise acquisition of gait information. Meanwhile, it is lightweight, thin, and comfortable to wear, providing an unobtrusive way to perform the gait monitoring. Furthermore, a smartphone graphic user interface is developed to display the sensor data in real-time via Bluetooth low energy. We perform a set of experiments in four real-life scenes including hallway walking, ascending/descending stairs, and slope walking, where gait parameters and features are extracted. Finally, the limitation and improvement, wearability and usability, further work, and healthcare-related potential applications are discussed.
Diabetes mellitus claims millions of lives every year. It affects the body in various ways by leading to many serious illnesses and premature mortality. Heart and kidney diseases, which are caused by diabetes, are increasing at an alarming rate. In this paper, we report a study of a noninvasive measurement technique to determine the glucose levels in the human body. Current existing methods to quantify the glucose level in the blood are predominantly invasive that involve taking the blood samples using finger pricking. In this paper, we report a spectroscopy-based noninvasive glucose monitoring system to measure glucose concentration. Near-infrared transmission spectroscopy is used and in vitro experiments are conducted, as well as in vivo. Our experimental study confirms a correlation between the sensor output voltage and glucose concentration levels. We report a low-cost prototype of spectroscopy-based noninvasive glucose monitoring system that demonstrates promising results in vitro and establishes a relationship between the optical signals and the changing levels of blood–glucose concentration.
A MEMS based novel THz detector structure is designed and realized by micro fabrication. The detector is then characterized to extract its mechanical performance. Operating in 0.5-2THz band, the detector has a pixel size of 200μm×200μm. Bimaterial suspension legs consist of Parylene-C and titanium, the pair of which provides a high mismatch in coefficients of thermal expansion. The pixel is a suspended Parylene-C structure having a 200 nm-thick titanium metallization. Operation principle relies on conversion of absorbed THz radiation into heat energy on the pixel. This increases the temperature of the free-standing microstructure that is thermally isolated from the substrate. The increase in temperature induces mechanical deflection due to bimaterial springs. The detector is designed to deliver a detectivity (D*) of 2×109 cmHz-1/2/W and a refresh rate of 20Hz.
Wearable sensor technologies play a significant role in realizing personalized medicine through continuously monitoring an individual’s health state. To this end, human sweat is an excellent candidate for non-invasive monitoring as it contains physiologically rich information. Previously reported sweat-based and other non-invasive biosensors either can only monitor a single analyte at a time or lack on-site signal processing circuitry and sensor calibration mechanisms for accurate analysis of the physiological state. Given the complexity of sweat secretion, simultaneous and multiplexed screening of target biomarkers is critical and full system integration to ensure the accuracy of measurements is a necessity. Here, a mechanically flexible and fully-integrated perspiration analysis system is presented that simultaneously and selectively measures sweat metabolites (e.g. glucose and lactate) and electrolytes (e.g. sodium and potassium ions), as well as the skin temperature to calibrate the sensors' response. Our work bridges the technological gap between signal transduction, conditioning, processing and wireless transmission in wearable biosensors by merging plastic-based sensors that interface with the skin, and silicon integrated circuits consolidated on a flexible circuit board for complex signal processing. The envisioned application could not have been realized by either of the technologies alone due to their respective inherent limitations. This wearable system is used to measure the detailed sweat profile of human subjects engaged in prolonged indoor and outdoor physical activities, and infer real-time assessment of the physiological state of the subjects. The platform enables a wide range of personalized diagnostic and physiological monitoring applications.
The use of a moisture sensor, based on microwave absorption at 40 GHz, is explored for the direct determination of the water content in milk. The operating principle of the device is based on the relative decrement of a transmitted signal through the sample. The results of the study are based on the measurements of over 150 samples of milk, taken from individual cows, from bulk tank milk and from skimmed milk sources. A high correlation is revealed between the signal absorption, measured by the sensor, and the nominal main solids content in bovine milk, determined independently. In addition, the fat concentrations in raw milk, considered separately from the other constituents, were also well correlated to the microwave moisture meter readings. As the other solid fractions of milk show less or non-significant correlation to the absorption coefficient, it is concluded that the correlation of fat to signal decrement is due to an excluded volume effect.
An extremely compact metamaterial microstrip sensor based on complementary split-ring-resonators (CSRRs) has been fabricated for chemical sensing. This device exhibits a resonance with high rejection at 4.5 GHz, which demonstrates concomitant variations when exposed to liquids of various permittivity values. The resonance frequency of CSRR is sensitive to the change in nearby dielectric material. The sensing of petrol shows a shift in frequency with a sharp dip in transmission, while, with ethanol, the frequency shift CSRRs is accompanied with increase in the power of the signal. The ultra-fast reversibility and repeatability offers good headway towards hybrid fuel sensing applications. (C) 2014 AIP Publishing LLC.
A wireless vibratory strain sensing system, which consists of a passive wireless sensor and a dynamic wireless interrogator, is presented in this paper. The wireless sensor utilizes a microstrip patch antenna as the strain sensing element since its resonant frequency is a function of the tensile strain it experiences. A dynamic wireless interrogator that is based on the principle of frequency modulated continuous wave radar and permits real-time monitoring of the antenna resonant frequency was designed and validated. The principle of operation of the dynamic wireless sensing system was first described, followed by the description of the design and implementation of the antenna-sensor node as well as the wireless interrogator. After calibrating the antenna-sensor response using static tensile tests, vibratory tensile tests were carried out by subjecting the test specimen to sinusoidal tensile loading at different frequencies. Antenna strain sensing accuracy was evaluated by comparing the strain readings from the antenna-sensor and the reference foil strain gauge. It reveals that the antenna-based strain sensing system has good dynamic strain tracking ability.
A multiband Fractal Koch dipole textile antenna is proposed for wearable applications. The antenna is designed to operate at 0.9 GHz, 2.45 GHz and 5.8 GHz. Denim materials as the substrate are selected aiming to obtain robustness, flexibility and a lightweight textile antenna. The antenna model is designed, simulated, optimized and analyzed using Microwave Studio CST software. Two types of multiband antenna prototypes are fabricated and evaluated with different conducting elements (Shield It fabric and copper foil tape). Antenna performance is observed in terms of return loss, bandwidth, radiation pattern and realized gain. Three different comprehensive analyses are taken into consideration: measurement antenna with different bending sizes, on-body measurement and under wet conditions. The antenna performances are evaluated based on resonant frequency (fo) and bandwidth (BW). The antennas performance with bending on the human body (arm & forearm) is compared and investigated. A suitable placement on the body has been discovered between the chest and backside. The antennas have also been tested under wet conditions to ensure a stable characteristic under the influence of water.
Poly(3,4-ethylenedioxythiophene)/Poly(styrenesulfonate) (PEDOT/PSS) is a widely used conductive polymer in the field of flex- ible electronics. The ways its microstructure changes over a broad range of temperature remain not well understood. This paper describes microstructure changes at different temperatures, and correlates microstructure with its physical properties (mechanical and electrical). We used High-Angle Annular Dark-Field Scanning Electron Microscopy (HAADF-STEM) combined with elec- tron energy loss spectroscopy (EELS) to determine the morphology and element atomic ratio of the film at different temperatures. These results together with the Atomic Force Microscopy (AFM) analysis, provide the foundation for a model of how temper- ature affects the microstructure of PEDOT/PSS. Moreover, dynamic mechanical analysis (DMA) and electrical characterization were performed to analyze the microstructure and physical property correlations
A soft tactile sensor able to detect both normal and tangential forces is fabricated with a simple method using conductive textile. Owing to the multi-layered architecture, the capacitive-based tactile sensor is highly sensitive (less than 10 mg and 8 μm, for minimal detectable weight and displacement, respectively) within a wide normal force range (potentially up to 27 N (400 kPa)) and natural touch-like tangential force ranges (from about 0.5 N to 1.8 N). Being flexible, soft, and low cost, this sensor represents an original approach in the emulation of natural touch. © 2014 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
In this paper, an RF identification sensor system is developed. It comprises passive sensors and an ultra-wideband (UWB) reader. The sensors are based on time-coded chipless tags. They consist of an UWB antenna connected to a delay line that is, in turn, loaded with a resistive temperature sensor. This sensor modulates the amplitude of the backscattered signals as a function of the temperature. The sensor tags are identified by changing the length of the delay line. In this paper, the operation principle and design of time-coded tags is presented and the integration of sensors in these tags is addressed. In addition, two measurement techniques are compared to implement the UWB reader. The first one is based on frequency sweeping and uses a vector network analyzer. The second one is based on a low-cost UWB radar. A full characterization of the sensor system is provided.
Surface-enhanced infrared absorption spectroscopy has attracted increased attention for direct access to molecular vibrational fingerprints in the mid-infrared. Perfect-absorber metamaterials (PAMs) with multi-band spectral responses and significant enhancement of the local near-field intensity were developed to improve the intrinsic absorption cross sections of absorption spectrum to identify the vibrational spectra of biomolecules. To verify its performance, the proposed infrared PAM array was used to identify the molecular stretches of a Parylene C film. The resonant responses of the infrared PAMs were accurately tuned to the vibrational modes of the C = C target bonds. The vibrational stretches of the C = C moiety were observed and the auto-fluorescence mechanisms of the Parylene C film were monitored. The unique properties of the PAMs indicate that this approach is a promising strategy for surface-enhanced molecular absorption spectroscopy (SEMS) in the mid-infrared region and for the tracking of characteristic molecular vibrational modes.
This paper presents 1 the design, fabrication, and characterization of a microwave resonator as a tool for concentration measurements of liquid compounds. The sensing device is a rectangular waveguide cavity tuned at 1.91 GHz, which exploits the fundamental TE101 mode in a transmission-type configuration. The coupling structure is optimized by means of a finite element code so as to achieve a high Q-factor. According
to the type of substance inside the mixture, its concentration is conveniently related to changes of the S21 scattering parameter (transmission coefficient) in terms of: 1) resonance frequency; 2) 3-dB bandwidth; and 3) amplitude at the resonance frequency. Experimental tests on liquid solutions in controlled conditions are presented to evaluate the performance of the device.
The assessment of the petroleum products quality often involves multiple indicators, among which water content and acid value are the two major parameters. The complexity of oil sample and narrow space in pipeline transport makes it difficult to monitor oil quality in real time. Considered the practical requirements, a new type of flexible microstrip sensor is proposed in this work. The shape and line width of the microstrip sensor are studied and optimized by theory and experiments. The proposed square spiral-based microstrip sensor has good water content detection resolution at high frequency with less acid interference and it can determine the acid value in low frequency band. The sensor surface is further passivated, protecting it from direct contact with the oil sample to enhance the electrochemical robustness, and still achieves good detection linearity and high sensitivity. After encapsulation on flexible substrate, the proposed microstrip sensor realized the non-contact determination of the water content and acid value of oil at the same time, which is only a few millimeters in size, and can conform to various tubing wall shapes. Due to the fact that the manufacture of the sensor is CMOS-compatible, we expect it to be readily applied to many other miniaturized chemical sensing applications.
Development of wearable devices for continuous respiration monitoring is of great importance for evaluating human health. Here, we propose a new strategy to achieve rapid respiration response by confining conductive polymers into 1D nanowires which facilitates the water molecules absorption/desorption and maximizes the sensor response to moisture. The nanowires arrays were fabricated through a low-cost nanoscale printing approach on flexible substrate. The nanoscale humidity sensor shows a high sensitivity (5.46%) and ultrafast response (0.63 s) when changing humidity between 0 and 13% and can tolerate 1000 repetitions of bending to a curvature radius of 10 mm without influencing its performance. Benefited by its fast response and low power assumption, the humidity sensor was demonstrated to monitor human respiration in real time. Different respiration patterns including normal, fast and deep respiration can be distinguished accurately.
In article 1900671, Qiannan Xue, Xuexin Duan, and co‐workers demonstrate a nanoscale impedimetric immunosensor based on biotin doped conductive polymer nanowire arrays which are fabricated through simple solution printing approach. This sensor can be a general platform for various bio‐analytical applications with ultrahigh sensitivity.
Point-of-care (POC) diagnostics have shown excellent potential in rapid biological analysis and health/disease monitoring. Here, we introduce a versatile, cost-effective, flexible, and wearable POC biomarker patch for effective sweat collection and health monitoring. We design and fabricate channels/patterns on filter paper using wax printing technology, which can direct sweat to collection and biomarker detection zones on the proposed platform. The detection zones are designed to measure the amount of collected sweat, in addition to measuring the sweat pH, and glucose (a potential diabetic biomarker), and lactate concentrations. It is significantly challenging to measure glucose in human sweat by colorimetric methods due to the extremely low glucose levels found in this medium. However, we overcame this issue by effectively engineering our wearable biosensor for optimal intake, storage, and evaporation of sweat. Our design concentrates the colorant (indicator) into a small detection zone and significantly increases the sensitivity for the sweat glucose sensing reactions. The device can thus detect glucose in physiological glucose concentration range of 50–300 μM. This cost-effective and wearable biosensor can provide instant in situ quantitative results for targets of interests, such as glucose, pH, and lactate, when coupled with the imaging and computing functionalities of smartphones. Meanwhile, it is also feasible to extract the air-dried sweat from the storage zone for further ex situ measurements of a broader portfolio of biomarkers, leading to applications of our wearable biosensor in personalized nutrition and medicine.
This paper reports the fabrication of capacitive humidity sensors by integrating a graphene oxide sensing layer inside paper substrates. Graphene oxide sheets were self-assembled on the papers’ fibers. A comparative study between several sensors with different concentrations of graphene oxide and different processing times in the graphene oxide suspension is reported. Its aim is to optimize the sensing layer in terms of concentration and thickness towards the fabrication of highly sensitive and porous sensors. The morphology of the fabricated sensors was characterized using scanning electron microscopy, their structure and chemical composition using Raman and infrared spectroscopies. The washability and mechanical strength of the graphene oxide coated paper were tested in water and in an ultrasonic bath. Last, the sensing capabilities of the fabricated devices were tested for a relative humidity ranging from 30% to 90% RH. The optimal sensor is highly porous, hydrophobic and exhibits a good response towards humidity with a low hysteresis. This work presents a low cost alternative for the use of polymers and coated-papers as substrates for flexible electronics. It is also a first step towards the integration of flexible electronics into substrates, which enables the fabrication of highly porous, economical and flexible devices ideal for air flow monitoring, e-dressings and e-textiles.
Flexible and stretchable polyurethane/carbon nanotube composite with strain detection ability was used for human breath monitoring. The composite material consisted of a network of multiwalled carbon nanotubes and thermoplastic high elastic polyurethane. It was found that elongation of the composite led to a macroscopic increase in electrical resistance, which can be used as a principle for applied strain detection. This detection was reversible, durable, and sensitive with gauge factor reaching very promising value, as, for example, ~46 at applied deformation of 8.7%. Further, the composite could be elongated to very large extend of deformation without discontinuity in measured resistance change reaching gauge factor ~ 450 at composite mechanical break at ~300% of strain. Sensor durability was also confirmed by sine wave deformation cycling when any decrease in the sensor properties for more than 103 cycles was observed. Simultaneously, the prepared composite possessed other utility properties also and was considered as multifunctional when it was tested as an organic solvent vapor sensor, an element for Joule heating and finally as a microstrip antenna.
Flexible ammonia (NH3) sensors based on one-dimensional nanostructures have attracted great attention due to their high flexibility and low-power consumption. However, it is still challenging to reliably and cost-effectively fabricate ordered nanostructure-based flexible sensors. Herein, a smartphone-enabled fully integrated system based on a flexible nanowire sensor was developed for real-time NH3 monitoring. Highly aligned, sub-100 nm nanowires on a flexible substrate fabricated by facile and low-cost soft lithography were used as sensitive elements to produce impedance response. The detection signals were sent to a smartphone and displayed on the screen in real time. This nanowire-based sensor exhibited robust flexibility and mechanical durability. Moreover, the integrated NH3 sensing system presented enhanced performance with a detection limit of 100 ppb, as well as high selectivity and reproducibility. The power consumption of the flexible nanowire sensor was as low as 3 μW. By using this system, measurements were carried out to obtain reliable information about the spoilage of foods. This smartphone-enabled integrated system based on a flexible nanowire sensor provided a portable and efficient way to detect NH3 in daily life.
A new aptamer-based lateral flow strip assay has been designed and developed for on-site rapid detection of cortisol in sweat. Cortisol in sweat has been identified as a key biomarker to monitor physiological stress. A highly sensitive and specific cortisol sensor was achieved by conjugating cortisol-selective aptamers to the surface of gold nanoparticles (AuNPs). Aptamer-functionalized AuNPs are stable against salt-induced aggregation. When cortisol molecules are present in the sample, they interact with the designed aptamers causing their desorption from the AuNP surface. Free AuNPs can then be captured by reaction with cysteamine immobilized on the test zone of the lateral flow test strip. This enables the visual detection of cortisol within minutes. Important parameters that affect the detection sensitivity in both solution and lateral flow assays, such as the loading density of aptamers per AuNP, salt and cysteamine concentrations, were investigated to provide the optimum assay performance. This hand-held device successfully exhibited a visual limit of detection of 1 ng/mL, readily covering the normal range of free cortisol in sweat (8–140 ng/mL). No significant cross reactivity to other stress biomarkers was observed. The advantages of this paper-based biosensor over previously reported test strips include the use of aptamers (which are more stable, simpler to use and lower cost than antibodies) and a simplified lateral flow assay (LFA) strip design (without the use of complementary aptamers in the test line). The resulting LFA aptasensor provides a rapid, sensitive, user-friendly and cost-effective point of care device for cortisol detection in sweat and other biofluids.
In this paper, we propose a humidity sensor based on a negative resistance oscillator using conducting polymer (CP) PEDOT:PSS film at room temperature. The proposed humidity sensor basically consists of a microstrip line and a negative resistance circuit, which creates a negative resistance for high-frequency oscillation. The microstrip line has a circuit structure that is connected through a via hole between the ground plane and the signal line with a CP thin film. From our experimental results, we find that the oscillation frequency of the sensor gradually decreases as the relative humidity (RH) increases. Owing to the conductivity variation of the CP film with the RH value, the oscillation frequency of the sensor sensitively changes in real time. Therefore, we suggest that our microwave-oscillator-based sensor scheme is a good candidate for the design of a robust and stable humidity sensor.
Profuse medical information about cardiovascular properties can be gathered from pulse waveforms. Therefore, it is desirable to design a smart pulse monitoring device to achieve noninvasive and real-time acquisition of cardiovascular parameters. The majority of current pulse sensors are usually bulky or insufficient in sensitivity. In this work, a graphene-based skin-like sensor is explored for pulse wave sensing with features of easy use and wearing comfort. Moreover, the adjustment of the substrate stiffness and interfacial bonding accomplish the optimal balance between sensor linearity and signal sensitivity, as well as measurement of the beat-to-beat radial arterial pulse. Compared with the existing bulky and nonportable clinical instruments, this highly sensitive and soft sensing patch not only provides primary sensor interface to human skin, but also can objectively and accurately detect the subtle pulse signal variations in a real-time fashion, such as pulse waveforms with different ages, pre-and post-exercise, thus presenting a promising solution to home-based pulse monitoring.
Wearable, flexible healthcare devices, which can monitor health data to predict and diagnose disease in advance, benefit society. Toward this future, various flexible and stretchable sensors as well as other components are demonstrated by arranging materials, structures, and processes. Although there are many sensor demonstrations, the fundamental characteristics such as the dependence of a temperature sensor on film thickness and the impact of adhesive for an electrocardiogram (ECG) sensor are yet to be explored in detail. In this study, the effect of film thickness for skin temperature measurements, adhesive force, and reliability of gel-less ECG sensors as well as an integrated real-time demonstration is reported. Depending on the ambient conditions, film thickness strongly affects the precision of skin temperature measurements, resulting in a thin flexible film suitable for a temperature sensor in wearable device applications. Furthermore, by arranging the material composition, stable gel-less sticky ECG electrodes are realized. Finally, real-time simultaneous skin temperature and ECG signal recordings are demonstrated by attaching an optimized device onto a volunteer's chest.
This paper reports a surface functionalization strategy for protein detections based on biotin-derivatized poly(L-lysine)-grafted oligo-ethylene glycol (PLL-g-OEGx-Biotin) copolymers. Such strategy can be used to attach the biomolecule receptors in a reproducible way simply by incubation of the transducer element in a solution containing such copolymers which largely facilitated the sensor functionalization at an industrial scale. As the synthesized copolymers are cationic in physiology pH, surface biotinylation can be easily achieved via electrostatic adsorption on negatively charged sensor surface. Biotinylated receptors can be subsequently attached through well-defined biotin-streptavidin interaction. In this work, the bioactive sensor surfaces were applied for mouse IgG and prostate specific antigen (PSA) detections using quartz crystal microbalance (QCM), optical sensor (BioLayer Interferometry) and conventional ELISA test (colorimetry). A limit of detection (LOD) of 0.5 nM was achieved for PSA detections both in HEPES buffer and serum dilutions in ELISA tests. The synthesized PLL-g-OEGx-Biotin copolymers with different OEG chain length were also compared for their biosensing performance. Moreover, the surface regeneration was achieved by pH stimulation to remove the copolymers and the bonded analytes, while maintaining the sensor reusability as well. Thus, the developed PLL-g-OEGx-Biotin surface assembling strategy is believed to be a versatile surface coating method for protein detections with multi-sensor compatibility.
The rational design of high-performance flexible pressure sensors attracts attention because of the potential applications in wearable electronics and human-machine interfacing. For practical applications, pressure sensors with high sensitivity and low detection limit are desired. Here, ta simple process to fabricate high-performance pressure sensors based on biomimetic hierarchical structures and highly conductive active membranes is presented. Aligned carbon nanotubes/graphene (ACNT/G) is used as the active material and microstructured polydimethylsiloxane (m-PDMS) molded from natural leaves is used as the flexible matrix. The highly conductive ACNT/G films with unique coalescent structures, which are directly grown using chemical vapor deposition, can be conformably coated on the m-PDMS films with hierarchical protuberances. Flexible ACNT/G pressure sensors are then constructed by putting two ACNT/G/PDMS films face to face with the orientation of the ACNTs in the two films perpendicular to each other. Due to the unique hierarchical structures of both the ACNT/G and m-PDMS films, the obtained pressure sensors demonstrate high sensitivity (19.8 kPa(-1), <0.3 kPa), low detection limit (0.6 Pa), fast response time (<16.7 ms), low operating voltage (0.03 V), and excellent stability for more than 35 000 loading-unloading cycles, thus promising potential applications in wearable electronics.
Composite nanofibers of Eu3+ doped poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDFHFP))/graphene are prepared by the electrospinning technique for the fabrication of ultrasensitive wearable piezoelectric nanogenerators (WPNGs) where the post-poling technique is not necessary. It is found that the complete conversion of the piezoelectric β-phase and the improvement of the degree of crystallinity is governed by the incorporation of Eu3+ and graphene sheets into P(VDF-HFP) nanofibers. The flexible nanocomposite fibers are associated with a hypersensitive electronic transition that results in an intense red light emission, and WPNGs also have the capability of detecting external pressure as low as ~23 Pa with a higher degree of acoustic sensitivity, ~11 V Pa–1,than has ever been previously reported. This means that ultrasensitive WPNGs can be utilized to recognize human voices, which suggests they could be a potential tool in the biomedical and national security sectors. The capacitor’s ability to charge from abundant environmental vibrations, such as music, wind, body motion, etc, drives WPNGs as a power source for portable electronics. This fact may open up the prospect of using the Eu3+ doped P(VDF-HFP)/graphene composite electrospun nanofibers, with their multifunctional properties such as vibration sensitivity, wearability, red light emission capability and piezoelectric energy harvesting, for various promising applications in portable electronics,health care monitoring, noise detection and security monitoring.
We demonstrate a wearable, flexible electrochemical biosensor for the combinatorial label-free detection of glucose in human sweat. The novel device comprises of stacked metal/metal-oxide (gold/zinc oxide) thin films within porous polyamide substrates for low-volume ultrasensitive impedance based detection of glucose and cortisol using non-faradaic electron-ionic charge transfer. In this work, we report the detection of glucose over a concentration range from 0.01–200 mg/dL spiked in synthetic and human sweat. Monoclonal antibodies specific to glucose oxidase were immobilized on thiolated ZnO sensing electrode surfaces resulting in the modulation of charge transfer within the electrical double layer (EDL). Non-Faradaic electrochemical impedance spectroscopy (EIS) was used to calibrate the sensor response with varying dose concentration through measurement of change in impedance. Reliable limit of detection (LOD) of 0.1 mg/dL in human sweat was demonstrated. Correlation of the sensor response with that of a commercial glucose meter TRUEresult™ Sensor (LOD of 20 mg/dL in blood) was found to be 0.9. Combinatorial detection of glucose and cortisol was demonstrated through frequency specific EIS measurements. Sensor variability was found to be within 15% of individual dynamic range for each molecule.
We report on a bimetallic, bifunctional electrode where a platinum (Pt) surface was patterned with nanostructured gold (Au) fingers with different film thicknesses, which was functionalized with glucose oxidase (GOx) to yield a highly sensitive glucose biosensor. This was achieved by using selective adsorption of a self-assembled monolayer (SAM) onto Au fingers, which allowed GOx immobilization only onto the Au-SAM surface. This modified electrode was termed bifunctional because it allowed to simultaneously immobilize the biomolecule (GOx) on gold to catalyze glucose, and detect hydrogen peroxide on Pt sites. Optimized electrocatalytic activity was reached for the architecture Pt/Au-SAM/GOx with 50 nm thickness of Au, where synergy between Pt and Au allowed for detection of hydrogen peroxide (H2O2) at a low applied potential (0 V vs. Ag/AgCl). Detection was performed for H2O2 in the range between 4.7 and 102.7 nmol L–1, with detection limit of 3.4 × 10−9 mol L−1 (3.4 nmol L−1) and an apparent Michaelis-Menten rate constant of 3.2×10−6 mol L−1, which is considerably smaller than similar devices with monometallic electrodes. The methodology was validated by measuring glucose in artificial saliva, including in the presence of interferents. The synergy between Pt and Au was confirmed in electrochemical impedance spectroscopy measurements with an increased electron transfer, compared to bare Pt and Au electrodes. The approach for fabricating the reproducible bimetallic Pt/Au electrodes is entirely generic and may be explored for other types of biosensors and biodevices where advantage can be taken of the combination of the two metals.
In this work, we present a clinical prototype with a wearable patient interface for microwave breast cancer detection. The long-term aim of the prototype is a breast health monitoring application. The system operates using multistatic time-domain pulsed radar, with 16 flexible antennas embedded into a bra. Unlike the previously reported, table-based prototype with a rigid cup-like holder, the wearable one requires no immersion medium and enables simple localization of breast surface. In comparison with the table-based prototype, the wearable one is also significantly more cost-effective and has a smaller footprint. To demonstrate the improved functionality of the wearable prototype, we here report the outcome of daily testing of the new, wearable prototype on a healthy volunteer over a 28-day period. The resulting data (both signals and reconstructed images) is compared to that obtained with our table-based prototype. We show that the use of the wearable prototype has improved the quality of collected volunteer data by every investigated measure. This work demonstrates the proof-of-concept for a wearable breast health monitoring array, which can be further optimized in the future for use with patients with various breast sizes and tissue densities.
The generalized polynomial chaos theory is com-bined with a dedicated cavity model for curved textile antennas to statistically quantify variations in the antenna's resonance frequency under randomly varying bending conditions. The non-intrusive stochastic method solves the dispersion relation for the resonance frequencies of a set of radius of curvature realizations corresponding to the Gauss quadrature points belonging to the orthogonal polynomials having the probability density function of the random variable as a weighting function. The formalism is applied to different distributions for the radius of curvature, either using a priori known or on-the-fly constructed sets of orthogonal polynomials. Numerical and experimental validation shows that the new approach is at least as accurate as Monte Carlo simulations while being at least 100 times faster. This makes the method especially suited as a design tool to account for performance variability when textile antennas are deployed on persons with varying body morphology.
In this study, a planar split-ring resonator (SRR)-based RF biosensor was developed for label-free detection of biomolecules such as the prostate cancer marker, prostate specific antigen (PSA), and cortisol stress hormone. The biosensor has a resonance-assisted transducer and is excited by a time-varying magnetic field component of a local high-impedance microstrip line. The resulting device exhibits an intrinsic S21 resonance with a quality-factor (or Q-factor) of 50. For the biomolecular interaction, anti-PSA and anti-cortisol were immobilized on the gold surface of the resonator by a protein-G mediated bioconjugation process and corresponding frequency shifts of Δf1p=30±2 MHz (for anti-PSA) and Δf1c=20±3 MHz (for anti-cortisol) were observed. The additional frequency shift of each PSA and cortisol antigen with a 100 pg/ml concentration was about 5 ± 1.5 MHz and 3 ± 1 MHz, respectively. From the experimental results, we confirmed that our device is very effective RF biosensor with a limit of detection (LOD) of 100 pg/ml and has sufficiently feasibility as a label-free biosensing scheme.
Printed electronics promise various kinds of sensor circuit labels, for applications in distributed sensing and monitoring, which can be manufactured using traditional printing tools at very low cost. Elevated humidity levels or water leakages cause tremendous costs in our society, such as in construction industries and in transportations. Distributed monitoring and remote sensing of the humidity level inside walls of buildings and packages is therefore desired and urgently needed. Here, we report a wireless humidity sensor label that is manufactured using screen-printing and dry-phase patterning. The sensor label includes a planar antenna, a tuning capacitor and a printed sensor-capacitor head. Through electromagnetic coupling between a reader and the printed sensor label, changes in humidity level were remotely detected and read-out as a shift of the resonant frequency. The manufacturing process of the humidity sensor label is fully compatible with inexpensive, reel-to-reel processing technologies, thus enabling low cost production.
We fabricated a series of gold nanowires/alumina composite films with different wire lengths. Optical transmission measurements confirmed that the composite films exhibit transverse and longitudinal surface plasmon resonances. We show that the wavelength of the longitudinal resonance is sensitive to nanowire length, while that of the transverse resonance is not. The experimental results are in agreement with the modeled results based on the Maxwell Garnett effective medium theory. Moreover, the window for negative refraction of the samples can be tuned in synchronism with the longitudinal resonance by the nanowire length.
A novel microwave nondestructive evaluation (NDE) sensor was developed in an attempt to increase the sensitivity of the microwave NDE method for detection of material defects small relative to a wavelength. The sensor was designed on the basis of a negative index material (NIM) lens. Transmission at the resonant frequency through the 1-D lens was determined to be about 10 times higher than that with the 2-D lens. However, the focusing ability of the 1-D lens was found to be slightly lower to the 2-D lens (focus spot size for the 1-D lens was determined to be 0.7λ vs. 0.48λ for the 2-D lens). A fiberglass material sample with a 3mm (0.037λ) diameter through hole (perpendicular to the propagation direction of the wave) was tested with both lenses. The hole was successfully detected with an 8.2cm wavelength electromagnetic wave with both lenses, but the image obtained with a 2-D lens was much sharper. Therefore, the choice of the lens to be used in a sensor is prescribed by the specific requirements of the testing system. For example, a 1-D lens should be considered when the simplicity of the testing system is deemed more important than the quality of the image obtained from a defect. A 1-D lens also allows for a longer sample standoff distance and higher transmission.
AZ series Mg alloys AZ31, AZ61, and AZ80 are widely applied in 3C (computer, communication, and consumer electronic) industry. Their corrosion characters in simulated sweat solution have been investigated by electrochemical technology, surface analysis, and pH measurements. Electrochemical test results showed that the three magnesium alloys revealed different corrosion resistance (Rt) in simulated sweat solution, Rt(AZ31)a<aR t(AZ61)a<aRt(AZ80). Three major components of simulated sweat solution played different roles during corrosion processes. Lactic acid was a kind of strong erosive medium for the magnesium alloys, and NaCl can induce pitting corrosion on alloys surface, while urea acted as a corrosion inhibitor. The corroded surface morphology of the three magnesium alloys was observed using scanning electron microscopy (SEM) and corrosion products were analyzed by X-ray diffraction (XRD). Result of pH measurement tests showed that there were differences in climbing speed and final values of pH for the three magnesium alloys in simulated sweat solution.
A simple analytical model, based on reaction-diffusion theory, is developed to predict the trade-off between average response (settling) time (ts) and minimum detectable concentration (&rgr;0) for nanobiosensors and nanochemical sensors. The model predicts a scaling relationship &rgr;0tsMD∼kD, where MD and kD are dimensionality dependent constants for one, two, and three dimensional nanosensors. We explore the performance limits of nanosensors using this analytical model and support its conclusions using detailed numerical simulation. Our results have obvious and significant implications for analyte density and response time reported in the literature and for design consideration of nanobiosensors and nanochemical sensors.
An extremely low operating electric field has been achieved on zinc oxide (ZnO) nanowire field emitters grown on carbon cloth. Thermal vaporization and condensation was used to grow the nanowires from a mixture source of ZnO and graphite powders in a tube furnace. An emission current density of 1 mA∕cm2 was obtained at an operating electric field of 0.7 V∕μm. Such low field results from an extremely high field enhancement factor of 4.11×104 due to a combined effect of the high intrinsic aspect ratio of ZnO nanowires and the woven geometry of carbon cloth.
The specular reflectance from a hexagonal array of gold nanorods embedded in an alumina matrix supported on an aluminum substrate is reported. The rods were grown by electrodeposition of gold in an alumina template and were oriented with their long axis perpendicular to the film surface. Optical reflectance measurements performed with an incident light beam of S polarization only exhibited the transverse surface plasmon resonance whereas the measurements obtained with P polarization exhibited both transverse and longitudinal resonances. A model for the reflectance from a thin anisotropic film was developed and shown to be in agreement with the experimental data.