Showing papers in "ACS Sensors in 2019"
TL;DR: The authors suggest that with the potential of these nanomaterials in sensing more research is needed on understanding their optical properties and why the synthetic methods influence their properties so much, into methods of surface functionalization that provide greater selectivity in sensing and into new sensing concepts that utilise the virtues of these nano-materials.
Abstract: Carbon and graphene quantum dots (CQDs and GQDs), known as zero-dimensional (0D) nanomaterials, have been attracting increasing attention in sensing and bioimaging. Their unique electronic, fluores...
570 citations
TL;DR: This Review places the focus on an in-depth summary of the recent technological advances that hold the potential for being incorporated into food packaging to ensure food quality, safety, or monitoring of spoilage.
Abstract: Food safety is a major factor affecting public health and the well-being of society. A possible solution to control food-borne illnesses is through real-time monitoring of the food quality throughout the food supply chain. The development of emerging technologies, such as active and intelligent packaging, has been greatly accelerated in recent years, with a focus on informing consumers about food quality. Advances in the fields of sensors and biosensors has enabled the development of new materials, devices, and multifunctional sensing systems to monitor the quality of food. In this Review, we place the focus on an in-depth summary of the recent technological advances that hold the potential for being incorporated into food packaging to ensure food quality, safety, or monitoring of spoilage. These advanced sensing systems usually target monitoring gas production, humidity, temperature, and microorganisms’ growth within packaged food. The implementation of portable and simple-to-use hand-held devices is als...
278 citations
TL;DR: It was conformed that Ti3C2 MXene theoreti-cally has a high selectivity to NH3, compared with other gases in this experiment, and the response of sensor toNH3 in-creased almost linearly with NH3 concentration from 10 to 700 ppm.
Abstract: In this study, from experiments and theoretical calculation, we reported that Ti3C2 MXene can be applied as sensors for NH3 detection at room temperature with high selectivity. Ti3C2 MXene, a novel two-dimensional carbide, was prepared by etching off Al atoms from Ti3AlC2. The as-prepared multilayer Ti3C2 MXene powders were delaminated to a single layer by intercalation and ultrasonic dispersion. The colloidal suspension of single-layer Ti3C2-MXene was coated on the surface of ceramic tubes to construct sensors for gas detection. Thereafter, the sensors were used to detect various gases (CH4, H2S, H2O, NH3, NO, ethanol, methanol, and acetone) with a concentration of 500 ppm at room temperature. Ti3C2 MXene-based sensors have high selectivity to NH3 compared with other gases. The response to NH3 was 6.13%, which was four times the second highest response (1.5% to ethanol gas). To understand the high selectivity, first-principles calculations were conducted to explore adsorption behaviors. From adsorption energy, adsorbed geometry, and charge transfer, it was confirmed that Ti3C2 MXene theoretically has a high selectivity to NH3, compared with other gases in this experiment. Moreover, the response of the sensor to NH3 increased almost linearly with NH3 concentration from 10 to 700 ppm. The humidity tests and cycle tests of NH3 showed that the Ti3C2 MXene-based gas sensor has excellent performances for NH3 detection at room temperature.
277 citations
TL;DR: The presented concepts and models are essential for understanding the complex role of additives and provide the basis for a knowledge-based design of gas sensors based on semiconducting metal oxide nanoparticles, which is outlined in a separate section.
Abstract: Introducing additives in semiconducting metal oxides includes, besides the use of filters, dynamic operation procedures and chemometric approaches, the most common way of tuning the sensitivity, selectivity, and stability of chemoresitsive gas sensors. For the vast majority of commercially used gas sensing materials, the introduction of additives is essential and is one of the longest lasting topics in gas sensor research. This Review discusses the different chemical and electrical sensitization mechanisms of additives as well as the role of different structures. Based on state-of-the-art experimental findings, this Review revises and updates the concepts that are used to explain the mechanisms through which the additives influence the performance of typical gas sensing materials, i.e., oxide nanoparticles arranged in a porous layer. The first sections classify the different additive structures, namely, doped or loaded oxides as well as mixtures of oxides, and describe the basic working principle of pristine semiconducting metal oxide gas sensors. The subsequent sections discuss different chemical and/or electrical contributions to the sensitization by additive structures, their mutual influence on each other, and the way they impact the sensing properties. The presented concepts and models are essential for understanding the complex role of additives and provide the basis for a knowledge-based design of gas sensors based on semiconducting metal oxide nanoparticles, which is outlined in a separate section.
237 citations
TL;DR: The performance of the fabricated V2CT x gas sensors in detection of nonpolar gases surpasses that of previously reported state-of-the-art gas sensors based on other 2D materials.
Abstract: The sensitive detection of explosive and flammable gases is an extremely important safety consideration in today’s industry. Identification of trace amounts of nonpolar analytes at ambient temperat...
206 citations
TL;DR: Key challenges that currently impede realization of breath sensors are described and strategies to overcome them are highlighted.
Abstract: Breath sensors can revolutionize medical diagnostics by on-demand detection and monitoring of health parameters in a noninvasive and personalized fashion. Despite extensive research for more than two decades, however, only a few breath sensors have been translated into clinical practice. Actually, most never even left the scientific laboratories. Here, we describe key challenges that currently impede realization of breath sensors and highlight strategies to overcome them. Specifically, we start with breath marker selection (with emphasis on metabolic and inflammatory markers) and breath sampling. Next, the sensitivity, stability, and selectivity requirements for breath sensors are described. Concepts are elaborated to systematically address these requirements by material design (focusing on chemoresistive metal oxides), orthogonal arrays, and filters. Finally, aspects of portable device integration, user communication, and clinical applicability are discussed.
197 citations
TL;DR: This work presents the most advanced platforms of this type, in which optimized chemistries, microfluidic designs, and device layouts enable accurate assessments not only of total loss of sweat and sweat rate but also of quantitatively accurate values of the pH and temperature of sweat, and of the concentrations of chloride, glucose, and lactate across physiologically relevant ranges.
Abstract: Real-time measurements of the total loss of sweat, the rate of sweating, the temperature of sweat, and the concentrations of electrolytes and metabolites in sweat can provide important insights into human physiology. Conventional methods use manual collection processes (e.g., absorbent pads) to determine sweat loss and lab-based instrumentation to analyze its chemical composition. Although such schemes can yield accurate data, they cannot be used outside of laboratories or clinics. Recently reported wearable electrochemical devices for sweat sensing bypass these limitations, but they typically involve on-board electronics, electrodes, and/or batteries for measurement, signal processing, and wireless transmission, without direct means for measuring sweat loss or capturing and storing small volumes of sweat. Alternative approaches exploit soft, skin-integrated microfluidic systems for collection and colorimetric chemical techniques for analysis. Here, we present the most advanced platforms of this type, in which optimized chemistries, microfluidic designs, and device layouts enable accurate assessments not only of total loss of sweat and sweat rate but also of quantitatively accurate values of the pH and temperature of sweat, and of the concentrations of chloride, glucose, and lactate across physiologically relevant ranges. Color calibration markings integrated into a graphics overlayer allow precise readout by digital image analysis, applicable in various lighting conditions. Field studies conducted on healthy volunteers demonstrate the full capabilities in measuring sweat loss/rate and analyzing multiple sweat biomarkers and temperature, with performance that quantitatively matches that of conventional lab-based measurement systems.
195 citations
TL;DR: An automated POC system for Ebola RNA detection with RNA-guided RNA endonuclease Cas13a, utilizing its collateral RNA degradation after its activation, establishing a key technology toward a useful POC diagnostic platform.
Abstract: Highly infectious illness caused by pathogens is endemic especially in developing nations where there is limited laboratory infrastructure and trained personnel. Rapid point-of-care (POC) serological assays with minimal sample manipulation and low cost are desired in clinical practice. In this study, we report an automated POC system for Ebola RNA detection with RNA-guided RNA endonuclease Cas13a, utilizing its collateral RNA degradation after its activation. After automated microfluidic mixing and hybridization, nonspecific cleavage products of Cas13a are immediately measured by a custom integrated fluorometer which is small in size and convenient for in-field diagnosis. Within 5 min, a detection limit of 20 pfu/mL (5.45 × 107 copies/mL) of purified Ebola RNA is achieved. This isothermal and fully solution-based diagnostic method is rapid, amplification-free, simple, and sensitive, thus establishing a key technology toward a useful POC diagnostic platform.
190 citations
TL;DR: The improvement of NH3 and humidity-sensing properties indicated that alkalized Ti3C2T x has great potential in chemical sensors, especially in NH 3 and humidity sensors.
Abstract: Ti3C2T x MXene with an organ-like structure was synthesized from Ti3AlC2 (MAX phase) through the typical hydrofluoric (HF) acid etching method. Ti3C2T x MXene was further alkaline-treated with a sodium hydroxide solution to obtain alkalized Ti3C2T x. Room-temperature planar-type gas- and humidity-sensing devices were also fabricated by utilizing Ti3C2T x MXene and alkalized Ti3C2T x sensing material based on the dip coating method, respectively. The intercalation of the alkali metal ion (Na+) and the increase of the surface terminal oxygen-fluorine ratio ([O]/[F]) in Ti3C2T x can effectively improve humidity- and gas-sensing properties at room temperature. The developed alkalized Ti3C2T x sensor exhibited excellent humidity-sensing characteristics (approximately 60 times response signal change) in the relative humidity (RH) with a range of 11-95% and considerable NH3 sensing performance (28.87% response value to 100 ppm of NH3) at room temperature. The improvement of NH3 and humidity-sensing properties indicated that alkalized Ti3C2T x has great potential in chemical sensors, especially in NH3 and humidity sensors.
183 citations
TL;DR: The design and attractive analytical performance of the new orthogonal wearable microneedle sensor array hold considerable promise for reliable, continuous, minimally invasive monitoring of L-Dopa in the ISF toward optimizing the dosing regimen of the drug and effective management of Parkinson disease.
Abstract: Levodopa is the most effective medication for treating Parkinson's disease (PD). However, because dose optimization is currently based on patients' report of symptoms, which are difficult for patients to describe, the management of PD is challenging. We report on a microneedle sensing platform for continuous minimally invasive orthogonal electrochemical monitoring of levodopa (L-Dopa). The new multimodal microneedle sensing platform relies on parallel simultaneous independent enzymatic-amperometric and nonenzymatic voltammetric detection of L-Dopa using different microneedles on the same sensor array patch. Such real-time orthogonal L-Dopa sensing offers a built-in redundancy and enhances the information content of the microneedle sensor arrays. This is accomplished by rapid detection of L-Dopa using square-wave voltammetry and chronoamperometry at unmodified and tyrosinase-modified carbon-paste microneedle electrodes, respectively. The new wearable microneedle sensor device displays an attractive analytical performance with the enzymatic and nonenzymatic L-Dopa microneedle sensors offering different dimensions of information while displaying high sensitivity (with a low detection limit), high selectivity in the presence of potential interferences, and good stability in artificial interstitial fluid (ISF). The attractive analytical performance and potential wearable applications of the microneedle sensor array have been demonstrated in a skin-mimicking phantom gel as well as upon penetration through mice skin. The design and attractive analytical performance of the new orthogonal wearable microneedle sensor array hold considerable promise for reliable, continuous, minimally invasive monitoring of L-Dopa in the ISF toward optimizing the dosing regimen of the drug and effective management of Parkinson disease.
155 citations
TL;DR: A self-powered and fully integrated smartwatch that consists of flexible photovoltaic cells and rechargeable batteries in the forms of a "watch strap", electrochemical glucose sensors, customized circuits, and display units integrated into a "dial" platform is successfully fabricated for real-time and continuous monitoring of sweat glucose levels.
Abstract: Wearable devices for health monitoring and fitness management have foreseen a rapidly expanding market, especially those for noninvasive and continuous measurements with real-time display that provide practical convenience and eliminated safety/infection risks. Herein, a self-powered and fully integrated smartwatch that consists of flexible photovoltaic cells and rechargeable batteries in the forms of a "watch strap", electrochemical glucose sensors, customized circuits, and display units integrated into a "dial" platform is successfully fabricated for real-time and continuous monitoring of sweat glucose levels. The functionality of the smartwatch, including sweat glucose sensing, signal processing, and display, can be supported with the harvested/converted solar energy without external charging devices. The Zn-MnO2 batteries serve as intermediate energy storage units and the utilization of aqueous electrolytes eliminated safety concerns for batteries, which is critical for wearable devices. Such a wearable system in a smartwatch fashion realizes integration of energy modules with self-powered capability, electrochemical sensors for noninvasive glucose monitoring, and in situ and real-time signal processing/display in a single platform for the first time. The as-fabricated fully integrated and self-powered smartwatch also provides a promising protocol for statistical study and clinical investigation to reveal correlations between sweat compositions and human body dynamics.
TL;DR: A field-effect transistor with a two-dimensional channel made of a single graphene layer to achieve label-free detection of DNA hybridization down to attomolar concentration, while being able to discriminate a single nucleotide polymorphism (SNP).
Abstract: In this work, we develop a field-effect transistor with a two-dimensional channel made of a single graphene layer to achieve label-free detection of DNA hybridization down to attomolar concentration, while being able to discriminate a single nucleotide polymorphism (SNP). The SNP-level target specificity is achieved by immobilization of probe DNA on the graphene surface through a pyrene-derivative heterobifunctional linker. Biorecognition events result in a positive gate voltage shift of the graphene charge neutrality point. The graphene transistor biosensor displays a sensitivity of 24 mV/dec with a detection limit of 25 aM: the lowest target DNA concentration for which the sensor can discriminate between a perfect-match target sequence and SNP-containing one.
TL;DR: This colorimetric assay based on an extended form of double-stranded DNA (dsDNA) self-assembly shielded gold nanoparticles (AuNPs) under positive electrolyte for detection of Middle East respiratory syndrome coronavirus (MERS-CoV) could discriminate down to 1 pmol/μL of 30 bp MERS- coV and further be adapted for convenient on-site detection of other infectious diseases, especially in resource-limited settings.
Abstract: Worldwide outbreaks of infectious diseases necessitate the development of rapid and accurate diagnostic methods. Colorimetric assays are a representative tool to simply identify the target molecules in specimens through color changes of an indicator (e.g., nanosized metallic particle, and dye molecules). The detection method is used to confirm the presence of biomarkers visually and measure absorbance of the colored compounds at a specific wavelength. In this study, we propose a colorimetric assay based on an extended form of double-stranded DNA (dsDNA) self-assembly shielded gold nanoparticles (AuNPs) under positive electrolyte (e.g., 0.1 M MgCl2) for detection of Middle East respiratory syndrome coronavirus (MERS-CoV). This platform is able to verify the existence of viral molecules through a localized surface plasmon resonance (LSPR) shift and color changes of AuNPs in the UV-vis wavelength range. We designed a pair of thiol-modified probes at either the 5' end or 3' end to organize complementary base pairs with upstream of the E protein gene (upE) and open reading frames (ORF) 1a on MERS-CoV. The dsDNA of the target and probes forms a disulfide-induced long self-assembled complex, which protects AuNPs from salt-induced aggregation and transition of optical properties. This colorimetric assay could discriminate down to 1 pmol/μL of 30 bp MERS-CoV and further be adapted for convenient on-site detection of other infectious diseases, especially in resource-limited settings.
TL;DR: The results demonstrate that controlling the interlayer transport of Ti3C2T x MXene is essential for enhancing the selective sensing of gas molecules.
Abstract: Gas molecules are known to interact with two-dimensional (2D) materials through surface adsorption where the adsorption-induced charge transfer governs the chemiresistive sensing of various gases. ...
TL;DR: Improved NO2 sensitive properties of the sensors based on RGO not only benefit from the effects of the heterostructures between SnO2 and ZnO, but also derived from the superior electrical characteristics of RGO.
Abstract: The employment of n-n homotypic heterogeneous junctions is an efficient method to improve sensitive performance of metal oxide-based gas sensors owing to the generation of charge accumulation regions. Herein, in order to further enhance nitrogen dioxide (NO2) sensing properties of the sensors based on reduced graphene oxide (RGO) at room temperature (RT), n-type ZnO nanoparticles (NPs) decorated n-type SnO2 NPs heterojunctions were successfully constructed on RGO nanosheets (NSs) by combination of the hydrothermal method and the wet-chemical deposition method. The formation of heterostructures between ZnO NPs and SnO2 NPs was confirmed by the nonlinear behavior of current versus voltage (I-V) curve of ZnO/SnO2-RGO. ZnO/SnO2-RGO based sensor displayed remarkably enhanced response (141.0%) for detecting 5 ppm of NO2 at RT, which is almost 4 and 3 times higher than that of SnO2-RGO (34.8%) and ZnO-RGO (43.3%), respectively. Moreover, as far as the ZnO/SnO2-RGO-based sensor is concerned, its response and recovery time (33 and 92 s) are also significantly decreased, compared to SnO2-RGO-based sensor (70 and 39 s) and ZnO-RGO-based sensor (272 and 1297 s). In this work, the improved NO2 sensing properties of the sensors based on RGO not only benefit from the effects of the heterostructures between SnO2 and ZnO, but also derive from the superior electrical characteristics of RGO. In particular, the n-n heterojunctions could offer facile access to effective electronic interaction and improve transfer efficiency of the charges at the interface to adsorbed oxygen. Meanwhile, the n-n heterojunctions can also provide additional reaction center for adsorbing gas.
TL;DR: The first disposable paper-based electrochemical wearable sensor that can monitor exhaled H2O2 in artificial breath calibration-free and continuously, in real time, and can be integrated into a commercial respiratory mask for on-site testing of exhaled breath is reported.
Abstract: Exhaled breath contains a large amount of biochemical and physiological information concerning one's health and provides an alternative route to noninvasive medical diagnosis of diseases. In the case of lung diseases, hydrogen peroxide (H2O2) is an important biomarker associated with asthma, chronic obstructive pulmonary disease, and lung cancer and can be detected in exhaled breath. The current method of breath analysis involves condensation of exhaled breath, is not continuous or real time, and requires two separate and bulky devices, complicating the periodic or long-term monitoring of a patient. We report the first disposable paper-based electrochemical wearable sensor that can monitor exhaled H2O2 in artificial breath calibration-free and continuously, in real time, and can be integrated into a commercial respiratory mask for on-site testing of exhaled breath. To improve precision for sensing H2O2, we perform differential electrochemical measurement by amperometry in which screen-printed Prussian Blue-mediated and nonmediated carbon electrodes are used for differential analysis. We were able to measure H2O2 in simulated breath in a concentration-dependent manner in real time, confirming its functionality. This proposed system is versatile, and by modifying the chemistry of the sensing electrodes, our method of differential sensing can be extended to continuous monitoring of other analytes in exhaled breath.
TL;DR: This work reviews the state of the art in noble metal nanoparticle-based multicolor colorimetric strategies adopted for visual quantification by the naked eye and proposes the future development of next-generationMulticolor qualification strategies.
Abstract: Noble metal nanoparticle-based colorimetric sensors have become powerful tools for the detection of different targets with convenient readout. Among the many types of nanomaterials, noble metal nanoparticles exhibit extraordinary optical responses mainly due to their excellent localized surface plasmon resonance (LSPR) properties. The absorption spectrum of the noble metal nanoparticles was mostly in the visible range. This property enables the visual detection of various analytes with the naked eye. Among numerous color change modes, the way that different concentrations of targets represent vivid color changes has been brought to the forefront because the color distinction capability of normal human eyes is usually better than the intensity change capability. We review the state of the art in noble metal nanoparticle-based multicolor colorimetric strategies adopted for visual quantification by the naked eye. These multicolor strategies based on different means of morphology transformation are classified into two categories, namely, the etching of nanoparticles and the growth of nanoparticles. We highlight recent progress on the different means by which biocatalytic reactions mediated LSPR modulation signal generation and their applications in the construction of multicolor immunoassays. We also discuss the current challenges associated with multicolor colorimetric sensors during actual sample detection and propose the future development of next-generation multicolor qualification strategies.
TL;DR: The ability to not only track, but also actively control plasma drug levels provides an unprecedented route towards improving therapeutic drug monitoring and, more generally, the personalized, high-precision delivery of pharmacological interventions.
Abstract: The electrochemical aptamer-based (E-AB) sensing platform appears to be a convenient (rapid, single-step, and calibration-free) and modular approach to measure concentrations of specific molecules (irrespective of their chemical reactivity) directly in blood and even in situ in the living body. Given these attributes, the platform may thus provide significant opportunities to render therapeutic drug monitoring (the clinical practice in which dosing is adjusted in response to plasma drug measurements) as frequent and convenient as the measurement of blood sugar has become for diabetics. The ability to measure arbitrary molecules in the body in real time could even enable closed-loop feedback control over plasma drug levels in a manner analogous to the recently commercialized controlled blood sugar systems. As initial exploration of this, we describe here the selection of an aptamer against vancomycin, a narrow therapeutic window antibiotic for which therapeutic monitoring is a critical part of the standard of care, and its adaptation into an electrochemical aptamer-based (E-AB) sensor. Using this sensor, we then demonstrate: (i) rapid (seconds) and convenient (single-step and calibration-free) measurement of plasma vancomycin in finger-prick-scale samples of whole blood, (ii) high-precision measurement of subject-specific vancomycin pharmacokinetics (in a rat animal model), and (iii) high-precision, closed-loop feedback control over plasma levels of the drug (in a rat animal model). The ability to not only track (with continuous-glucose-monitor-like measurement frequency and convenience) but also actively control plasma drug levels provides an unprecedented route toward improving therapeutic drug monitoring and, more generally, the personalized, high-precision delivery of pharmacological interventions.
TL;DR: A strain sensor fabricated using aerosol jet printing technology on a commercially available bandage to be used as a low-cost wearable that is stretchable and has good sensitivity and stability for 700 cycles of repeated bending is reported.
Abstract: Flexible and stretchable strain sensors are in great demand for many applications like wearables and home health. This work reports a strain sensor fabricated using aerosol jet printing technology on a commercially available bandage to be used as a low-cost wearable. Laser light is explored to sinter the silver nanoparticle ink on a low-temperature bandage substrate. The laser parameters, their effects on the microstructure of the film, and the resulting sensor performance are systematically investigated. The results showed that the sensor is stretchable and has good sensitivity and stability for 700 cycles of repeated bending.
TL;DR: A new sensing moiety, ortho-methoxy-methyl-ether incorporated electron donor (D)-acceptor (A) type naphthaldehyde provides high selectivity and sensitivity amidst its superiority within practical applications for sensing hydrazine.
Abstract: Hydrazine (N2H4) is one of the most important pnictogen hydride chemicals, and is utilized within a wide spectrum of industries. As a result of its extensive use, hydrazine’s monitoring methods have constantly come under fire due to its potential health risk and the subsequent environmental pollution. Fluorometric molecular sensing systems generally report with a major emphasis on the merit of fluorescence analysis. What we are proposing within this report is a next-generation fluorescent probe that allows hydrazine to become fully traceable, within multifarious environments that show fast and intuitional fluorescence transformation. A new sensing moiety, ortho-methoxy-methyl-ether (o-OMOM) incorporated electron donor (D)–acceptor (A) type naphthaldehyde provides high selectivity and sensitivity amidst its superiority within practical applications for sensing hydrazine. The new probe overcomes most of the drawbacks of currently used fluorescent probes, and due to its successful demonstrations, such as rea...
TL;DR: A brief Perspective on surface enhanced Raman scattering (SERS) tags is presented, regarding their composition, morphology, and structure, and their own selection from the current state-of-the-art is described, showing a gradual evolution from two-dimensional studies to three-dimensional analysis.
Abstract: We have recently witnessed a major improvement in the quality of nanoparticles encoded with Raman-active molecules (SERS tags). Such progress relied mainly on a major improvement of fabrication methods for building-blocks, resulting in widespread application of this powerful tool in various fields, with the potential to replace commonly used techniques, such as those based on fluorescence. We present hereby a brief Perspective on surface enhanced Raman scattering (SERS) tags, regarding their composition, morphology, and structure, and describe our own selection from the current state-of-the-art. We then focus on the main bioimaging applications of SERS tags, showing a gradual evolution from two-dimensional studies to three-dimensional analysis. Recent improvements in sensitivity and multiplexing ability have enabled great advancements toward in vivo applications, e.g., highlighting tumor boundaries to guide surgery. In addition, the high level of biomolecule sensitivity reached by SERS tags promises an expansion toward biomarker detection in cases for which traditional methods offer limited reliability, as a consequence of the frequently low analyte concentrations.
TL;DR: An entirely new class of printed electrical gas sensors that are produced at near “zero cost” are reported, exploiting the intrinsic hygroscopic properties of cellulose fibers within paper to enable the use of wet chemical methods for sensing without manually adding water to the substrate.
Abstract: We report an entirely new class of printed electrical gas sensors that are produced at near "zero cost". This technology exploits the intrinsic hygroscopic properties of cellulose fibers within paper; although it feels and looks dry, paper contains substantial amount of moisture, adsorbed from the environment, enabling the use of wet chemical methods for sensing without manually adding water to the substrate. The sensors exhibit high sensitivity to water-soluble gases (e.g., lower limit of detection for NH3 < 200 parts-per-billion) with a fast and reversible response. The sensors show comparable or better performance (especially at high relative humidity) than most commercial ammonia sensors at a fraction of their price (<$0.02 per sensor). We demonstrate that the sensors proposed can be integrated into food packaging to monitor freshness (to reduce food waste and plastic pollution) or implemented into near-field-communication tags to function as wireless, battery-less gas sensors that can be interrogated with smartphones.
TL;DR: This review mainly focuses on recent attempt on the key issues of in vivo electrochemical sensors including selectivity, tissue response and sensing reliability, and compatibility with electrophysiological techniques.
Abstract: In vivo electrochemical sensing based on implantable microelectrodes is a strong driving force of analytical neurochemistry in brain. The complex and dynamic neurochemical network sets stringent standards of in vivo electrochemical sensors including high spatiotemporal resolution, selectivity, sensitivity, and minimized disturbance on brain function. Although advanced materials and novel technologies have promoted the development of in vivo electrochemical sensors drastically, gaps with the goals still exist. This Review mainly focuses on recent attempts on the key issues of in vivo electrochemical sensors including selectivity, tissue response and sensing reliability, and compatibility with electrophysiological techniques. In vivo electrochemical methods with bare carbon fiber electrodes, of which the selectivity is achieved either with electrochemical techniques such as fast-scan cyclic voltammetry and differential pulse voltammetry or based on the physiological nature will not be reviewed. Following the elaboration of each issue involved in in vivo electrochemical sensors, possible solutions supported by the latest methodological progress will be discussed, aiming to provide inspiring and practical instructions for future research.
TL;DR: For the first time, room temperature NO2 sensing characteristics of 2D NbS2 nanosheets and the sensing mechanisms are reported and the important role of edge configuration of TMDs depending on synthetic conditions is presented for further studies.
Abstract: Transition metal dichalcogenides (TMDs) have attracted enormous attention in diverse research fields. Especially, gas sensors are considered in a promising application exploiting TMDs. However, the...
TL;DR: A novel genetically encoded pH probe is engineered by fusing the pH-stable cyan fluorescent protein (FP) variant, mTurquoise2, to the highly pH-sensitive enhanced yellow fluorescent protein, EYFP, which yielded a ratiometric biosensor—referred to as pH-Lemon—optimized for live imaging of distinct pH conditions within acidic cellular compartments.
Abstract: Distinct subcellular pH levels, especially in lysosomes and endosomes, are essential for the degradation, modification, sorting, accumulation, and secretion of macromolecules. Here, we engineered a novel genetically encoded pH probe by fusing the pH-stable cyan fluorescent protein (FP) variant, mTurquoise2, to the highly pH-sensitive enhanced yellow fluorescent protein, EYFP. This approach yielded a ratiometric biosensor—referred to as pH-Lemon—optimized for live imaging of distinct pH conditions within acidic cellular compartments. Protonation of pH-Lemon under acidic conditions significantly decreases the yellow fluorescence while the cyan fluorescence increases due to reduced Forster resonance energy transfer (FRET) efficiency. Because of its freely reversible and ratiometric responses, pH-Lemon represents a fluorescent biosensor for pH dynamics. pH-Lemon also shows a sizable pH-dependent fluorescence lifetime change that can be used in fluorescence lifetime imaging microscopy as an alternative observa...
TL;DR: In this article, an easy-handing, low-cost, light-weight, and conformable compatibility with clothes in wearable and portable smart electronics is presented for e-textiles.
Abstract: E-textiles are gaining growing popularity recently due to low cost, light weight, and conformable compatibility with clothes in wearable and portable smart electronics. Here, an easy-handing, low c...
TL;DR: A platform based on surface-enhanced Raman spectroscopy in combination with multivariate analysis is described, and it is demonstrated for the first time that this platform can distinguish among exosomes from different biological sources based on their Raman signature, a promising approach for developing exosome-based fingerprinting.
Abstract: Exosomes contain cell- and cell-state-specific cargos of proteins, lipids, and nucleic acids and play significant roles in cell signaling and cell-cell communication. Current research into exosome-based biomarkers has relied largely on analyzing candidate biomarkers, i.e., specific proteins or nucleic acids. However, this approach may miss important biomarkers that are yet to be identified. Alternative approaches are to analyze the entire exosome system, either by "omics" methods or by techniques that provide "fingerprints" of the system without identifying each individual biomolecule component. Here, we describe a platform of the latter type, which is based on surface-enhanced Raman spectroscopy (SERS) in combination with multivariate analysis, and demonstrate the utility of this platform for analyzing exosomes derived from different biological sources. First, we examined whether this analysis could use exosomes isolated from fetal bovine serum using a simple, commercially available isolation kit or necessitates the higher purity achieved by the "gold standard" ultracentrifugation/filtration procedure. Our data demonstrate that the latter method is required for this type of analysis. Having established this requirement, we rigorously analyzed the Raman spectral signature of individual exosomes using a unique, hybrid SERS substrate made of a graphene-covered Au surface containing a quasi-periodic array of pyramids. To examine the source of the Raman signal, we used Raman mapping of low and high spatial resolution combined with morphological identification of exosomes by scanning electron microscopy. Both approaches suggested that the spectra were collected from single exosomes. Finally, we demonstrate for the first time that our platform can distinguish among exosomes from different biological sources based on their Raman signature, a promising approach for developing exosome-based fingerprinting. Our study serves as a solid technological foundation for future exploration of the roles of exosomes in various biological processes and their use as biomarkers for disease diagnosis and treatment monitoring.
TL;DR: The development of a new type of ZIKV electrochemical biosensor based on surface imprinted polymers and graphene oxide composites is reported, which is similar to the detection limit of the real-time quantitative reverse transcription PCR method.
Abstract: Zika virus (ZIKV) is a flavivirus that was first identified in 1947. Initially, the virus was of little concern for health authorities given there were very few casualties among those suffering an infection. As such, only limited studies were performed on ZIKV. Recently, the viral infection has been linked to microcephaly in infants, which has prompted a dramatic increase in scientific interest in ZIKV research, including methods to allow for rapid virus identification. In this work we report the development of a new type of ZIKV electrochemical biosensor based on surface imprinted polymers and graphene oxide composites. The biosensor was used to detect ZIKV by measuring changes in the electrical signal with changing virus concentrations in buffer and serum using standard electrochemical techniques. The detection limit of our method is similar to the detection limit of the real-time quantitative reverse transcription PCR method.
TL;DR: The MXene/AuNRs composite constitute an efficient SERS platform for reliable and high-sensitivity environmental analysis and food safety monitoring and shows excellent sensitivity and quantitative detection.
Abstract: A reliable surface-enhanced Raman scattering (SERS) substrate composed of two-dimensional (2D) MXene (Ti3C2Tx) nanosheets and gold nanorods (AuNRs) is designed and fabricated for sensitive detection of organic pollutants. The AuNRs are uniformly distributed on the surface of the 2D MXene nanosheets because of the strong electrostatic interactions, forming abundant SERS hot spots. The MXene/AuNR SERS substrate exhibits high sensitivity and excellent reproducibility in the determination of common organic dyes such as rhodamine 6G, crystal violet, and malachite green. The detection limits are 1 × 10-12, 1 × 10-12, and 1 × 10-10 M, and relative standard deviations determined from 13 areas on each sample are 18.1, 10.1, and 15.6%, respectively. In the determination of more complex organic pesticides and pollutants, the substrate also shows excellent sensitivity and quantitative detection, and the detection limits for thiram and diquat of 1 × 10-10 and 1 × 10-8 M, respectively, are much lower than the contaminant levels stipulated by the US Environmental Protection Agency. The MXene/AuNR composite constitutes an efficient SERS platform for reliable and high-sensitivity environmental analysis and food safety monitoring.
TL;DR: This work proposed a new method based on carbon dots for selective and efficient detection of nitrite (NO2-), which was based on the interaction between the amine group of m-CDs and NO2- via a diazo reaction that produced diazonium salts and induced the fluorescence quenching of m -CDs.
Abstract: In this work, we proposed a new method based on carbon dots (named m-CDs) for selective and efficient detection of nitrite (NO2–), which was based on the interaction between the amine group of m-CDs and NO2– via a diazo reaction that produced diazonium salts and induced the fluorescence quenching of m-CDs. The concentration of NO2– shows a good linear relationship with a quenched fluorescence intensity from 0.063 to 2.0 μM (R2 = 0.996) with a detection limit of 0.018 μM. In addition, a ratiometric fluorescence probe (m-CDs@[Ru(bpy)3]2+) was constructed via electrostatic interaction by introducing Ru(bpy)3Cl2·6H2O as an internal reference fluorescent reagent. Interestingly, a transition of the fluorescent color of the ratiometric probe from cyan to red could be visually observed upon increasing the concentration of NO2–. Based on these findings, a ratiometric fluorescent-based portable agarose hydrogel test kit was fabricated and applied for on-spot assessment of NO2– content within 10 min. As far as we kn...