Showing papers in "Sensors and Actuators B-chemical in 2012"
TL;DR: Graphene, a monolayer of graphite sheet consisting of sp2 hybridized carbon atoms covalently bonded to three other atoms (discovered in 2004), has recently attracted the attention of chemical sensor researchers owing to its unprecedented structural, mechanical and electrical properties.
Abstract: Graphene, a monolayer of graphite sheet consisting of sp2 hybridized carbon atoms covalently bonded to three other atoms (discovered in 2004), has recently attracted the attention of chemical sensor researchers owing to its unprecedented structural, mechanical and electrical properties. Excellent mechanical strength (Young modulus ∼0.05 TPa), potentiality of ultrafast electron transport (highest mobility ∼200,000 cm 2 /V s) along with the best surface to volume ratio has opened up the opportunity to use the material for future gas and vapor sensors with ultra fast speed and long-term durability. Since it is a two dimensional material, every atom of graphene may be considered a surface atom and as a result every atom site may be involved in the gas interactions. This feature of graphene can eventually be responsible for its ultra sensitive sensor response with the lowest detection capability approaching even a single molecule. Further, the ease of functionalization of the material either by chemical means (absorption of many molecules like oxygen or hydrogen) or by application of voltage or pressure, facilitates bandgap-engineering which in turn may lead to a possible solution to the selectivity issues, the perennial problems of chemical sensors. In this review, the latest advancement and new perspectives of graphene based gas and vapor sensors have been discussed critically.
628 citations
TL;DR: This work introduced a machine learning approach, namely an ensemble of classifiers, to solve a gas discrimination problem over extended periods of time with high accuracy rates and performs better than the baseline competing methods.
Abstract: Sensor drift remains to be the most challenging problem in chemical sensing. To address this problem we have collected an extensive dataset for six different volatile organic compounds over a period of three years under tightly controlled operating conditions using an array of 16 metal-oxide gas sensors. The recordings were made using the same sensor array and a robust gas delivery system. To the best of our knowledge, this is one of the most comprehensive datasets available for the design and development of drift compensation methods, which is freely reachable on-line. We introduced a machine learning approach, namely an ensemble of classifiers, to solve a gas discrimination problem over extended periods of time with high accuracy rates. Experiments clearly indicate the presence of drift in the sensors during the period of three years and that it degrades the performance of the classifiers. Our proposed ensemble method based on support vector machines uses a weighted combination of classifiers trained at different points of time. As our experimental results illustrate, the ensemble of classifiers is able to cope well with sensor drift and performs better than the baseline competing methods.
537 citations
TL;DR: ZnO nanorods were fabricated by a simple low-temperature hydrothermal process in high yield (about 85%), starting with Zn(OH) 4 2− aqueous solution in the presence of CTAB, the CTA board serving as a structure director, and no calcination process was needed as discussed by the authors.
Abstract: ZnO nanorods were fabricated by a simple low-temperature hydrothermal process in high yield (about 85%), starting with Zn(OH) 4 2− aqueous solution in the presence of CTAB, the CTAB serving as a structure director, and no calcination process was needed. The morphology and crystal structure of the prepared ZnO nanorods were characterized by X-ray diffraction (XRD), Scanning electron microscope (SEM) and Transmission electron microscope (TEM). The ZnO nanorods were then used to construct a gas sensor for ethanol detection at different operating temperature. The as-prepared ZnO nanorod gas sensor exhibited a high, reversible and fast response to ethanol, indicating its potential application as a gas sensor to detect ethanol.
436 citations
TL;DR: In this article, the authors present an overview of the most recent developments in semiconducting NO x gas sensors based on these metal oxide nanostructures and their applications in vehicle exhaust and environmental monitoring.
Abstract: 21st century has already seen huge progress in science and technology of small, highly sensitive gas sensors, which can selectively detect environmental toxins like NO x – the oxides of nitrogen – a byproduct of fossil fuel combustion. Into this bargain, public became more health-aware and environmental bodies grew stricter, stimulating analytical and material scientists to find new strategies from material synthesis to fabrication of NO x sensors in order to produce fast and reliable gas detectors. To the scientists, semiconducting metal oxides, owing to their low cost, easy processing, high gas response, good electrical properties and above all tunable structure at the nanoscale, always presented a first-hand choice for sensor fabrication. This article presents an overview of the most recent developments in semiconducting NO x gas sensors based on these metal oxide nanostructures and their applications in vehicle exhaust and environmental monitoring. A strong emphasis is presented on chemiresistor and field effect transistor devices using semiconducting metal oxides as active layers. The performance levels of these NO x sensors are compared to those of other devices as well as other semiconductor materials. Furthermore, keeping in mind the ultimate user demands, limitations of the current sensor technologies and future strategies are discussed.
353 citations
TL;DR: In this article, the reaction between green synthesized silver nanoparticles (Ag NPs) and mercury (II) ions was introduced as a new and high potential colorimetric sensor for the selective recognition and monitoring of mercuric ions in aqueous samples.
Abstract: The reaction between biologically green synthesized silver nanoparticles (Ag NPs) and mercury (II) ions was introduced as a new and high potential colorimetric sensor for the selective recognition and monitoring of mercuric ions in aqueous samples. The green synthesized silver nanoparticles were characterized with surface plasmon resonance (SPR) ultraviolet spectroscopy (UV–vis), SEM and X-ray diffraction analysis (XRD) techniques. The fresh biologically synthesized silver nanoparticles are yellowish-brown in color due to the intense SPR absorption band. In the presence of Hg 2+ , the yellow Ag NPs solution was turned to colorless, accompanying the broadening and blue shifting of SPR band. The sensitivity and selectivity of green prepared Ag NPs toward other representative transition-metal ions, alkali metal ions and alkaline earth metal ions were studied. Also the effect of the concentration of Hg 2+ to the Ag NPs was considered and the LOD for mercury (II) ion was 2.2 × 10 −6 mol L −1 . The proposed method has been successfully used for the determination of mercury (II) ions in various water samples.
325 citations
TL;DR: In this article, a simple and reproducible method to improve the sensing performance of a graphene gas sensor using ozone treatment and demonstrate it with nitrogen dioxide (NO2) gas was reported.
Abstract: In the present study, we report a simple and reproducible method to improve the sensing performance of a graphene gas sensor using ozone treatment and demonstrate it with nitrogen dioxide (NO2) gas. The ozone-treated graphene (OTG) sensor demonstrated remarkable enhancement of the sensing performances such as percentage response, detection limit and response time. The percentage response of the OTG sensor was twofold higher than that of a pristine graphene sensor when it was exposed to 200 ppm concentration of NO2 at room temperature. It is noteworthy that significant improvement was achieved in the response time by a factor of 8. Extremely low parts-per-billion (ppb) concentrations were clearly detectable, while the pristine graphene sensor could not detect NO2 molecules below 10 ppm concentration. The detection limit of the OTG sensor was estimated to be 1.3 ppb based on the signal to noise ratio, which is the cutting-edge resolution. The present ozone treatment may provide an effective way to improve the performance of the graphene-based sensor, given its simple process, practical usability and cost effectiveness.
303 citations
TL;DR: This review provides an overview of the available biosensor platforms for the detection of various CVD markers and considerations of future prospects for the technology are addressed.
Abstract: The cardiovascular disease (CVD) is considered as a major threat to global health. Therefore, there is a growing demand for a range of portable, rapid and low cost biosensing devices for the detection of CVD. Biosensors can play an important role in the early diagnosis of CVD without having to rely on hospital visits where expensive and time-consuming laboratory tests are recommended. Over the last decade, many biosensors have been developed to detect a wide range of cardiac marker to reduce the costs for healthcare. One of the major challenges is to find a way of predicting the risk that an individual can suffer from CVD. There has been considerable interest in finding diagnostic and prognostic biomarkers that can be detected in blood and predict CVD risk. Of these, C-reactive protein (CRP) is the best known biomarker followed by cardiac troponin I or T (cTnI/T), myoglobin, lipoprotein-associated phospholipase A(2), interlukin-6 (IL-6), interlukin-1 (IL-1), low-density lipoprotein (LDL), myeloperoxidase (MPO) and tumor necrosis factor alpha (TNF-α) has been used to predict cardiovascular events. This review provides an overview of the available biosensor platforms for the detection of various CVD markers and considerations of future prospects for the technology are addressed.
302 citations
TL;DR: In this article, aldazine-based colorimetric chemosensors for Cu 2+ and Fe 3+ were developed by simple condensation of 4-diethylamino-salicylaldehyde and 8-hydroxyjulolidinal with hydrazine.
Abstract: We have developed novel aldazine-based colorimetric chemosensors for Cu 2+ and Fe 3+ . The aldazine ligands were synthesized by simple condensation of 4-diethylamino-salicylaldehyde and 8-hydroxyjulolidinal with hydrazine. The (4-diethylamino)-salicylaldehyde-azine ( SA ) showed high selectivity and sensitivity towards Cu 2+ over the other alkali and transition metal ions. In the presence of Cu 2+ , absorption band of SA at 425 nm red shifted to 545 nm. The color of solution changed from pale yellow to purple color. Interestingly, 8-hydroxyjulolidinal-azine ( JA ) showed selectivity towards Fe 3+ over alkali and transition metal ions. In the presence of Fe 3+ , the color of the ligand solution changed from pale yellow to violet. The absorption band of JA at 445 red shifted to 575 nm. The fluorescence of ligands SA and JA was completely quenched in the presence of Cu 2+ and Fe 3+ , respectively. However, the quenched fluorescence of JA –Fe 3+ complex can be reversibly restored using cysteine.
294 citations
TL;DR: In this paper, the interaction of pristine and Sc-doped boron nitride nanotubes (BNNTs) with the phosgene was investigated using density functional theory calculations in terms of Gibbs free energies, enthalpy changes, geometry, vibrational frequency, work function, and density of state analysis.
Abstract: Exploring a novel sensor for detection of toxic phosgene molecules, interaction of pristine and Sc-doped boron nitride nanotubes (BNNT) with the phosgene was investigated using density functional theory calculations in terms of Gibbs free energies, enthalpy changes, geometry, vibrational frequency, work function, and density of state analysis. It was found that unlike the pristine BNNTs, Sc-doped tubes can effectively interact with the phosgene molecule, so that their electronic properties and work functions are dramatically changed upon exposure to this molecule. We believe that doping the BNNTs with Sc may be a good strategy for improving the sensitivity of these tubes towards phosgene, which cannot be trapped and detected by the pristine BNNT.
279 citations
TL;DR: In this article, a single layer graphene decorated with palladium (Pd) nanoparticles is fabricated using a single-layer H 2 sensor, which is able to detect as low as 20ppm H 2 at room temperature (22°C).
Abstract: Flexible hydrogen gas (H 2 ) sensors are fabricated using a single layer graphene decorated with palladium (Pd) nanoparticles. Thermally evaporated Pd is generally deposited on a graphene in the form of nanoparticles when the deposition thickness is very small. The graphene sensor with Pd thickness of 3 nm exhibits a gas response of ∼33% when exposed to 1000 ppm H 2 and it is able to detect as low as 20 ppm H 2 at room temperature (22 °C). The sensor is so flexible that any significant degradation is not observed when it is bent to a curved geometry with a bending radius of 3 mm. The flexible hydrogen sensors are applicable to a broad range of systems with demanding mechanical flexibility, durability and high gas response.
274 citations
TL;DR: In this paper, the gas sensing studies revealed that ZnO/SnO2 exhibits a high response to NO2 at room temperature under UV light emitting diode illumination, and the highest response was achieved by the composite with Zn and Sn molar ratio of 1:1 (ZS3).
Abstract: ZnO/SnO2 composite materials are synthesized by hydrolyzing SnCl2 on ZnO nanorods via the wet chemical method. The gas sensing studies revealed that ZnO/SnO2 exhibits a high response to NO2 at room temperature under UV light emitting diode illumination. The highest response to NO2 was achieved by the ZnO/SnO2 composite with Zn and Sn molar ratio of 1:1 (ZS3). The resistance of sensor based on ZS3 with UV light stimulation changed 1266-fold to 500 ppb NO2 gas at room temperature. Furthermore, the selectivity, as well as response and recovery properties, of the sensor was improved remarkably by UV light irradiation. The ZnO/SnO2 heterojunction model and the increased photo-generated electrons are proposed to elucidate the gas sensing mechanism.
TL;DR: A facile one-pot strategy was developed for the assembly of gold nanoparticles (Au NPs) onto single crystalline ZnO nanorods using cetyltrimethylammonium bromide (CTAB) as a capping agent.
Abstract: A facile one-pot strategy was developed for the assembly of gold nanoparticles (Au NPs) onto single crystalline ZnO nanorods using cetyltrimethylammonium bromide (CTAB) as a capping agent. Zinc oxide nanorods were synthesized by hydrothermal method whereas the Au NPs (below 5 nm) were deposited on the surface of ZnO nanorods by the solution growth method. Gas sensing properties of Au/ZnO nanorods were studied at various temperatures for various concentrations of reducing (CO) and oxidizing (NO 2 ) gases in synthetic air and compared with pristine ZnO nanorods. Sensor fabricated by Au/ZnO nanorods showed significantly enhanced sensing performances for CO gas while opposite was the case with NO 2 gas as compared to pristine ZnO nanorods. The highest response of Au/ZnO nanorods for CO gas was 12 at 150 °C while for ZnO nanorods, it was 6.12 at 400 °C. Whereas the highest response of Au/ZnO nanorods for NO 2 gas was 4.14 while for ZnO nanorods, it was 10 at 300 °C. It was found that Au NPs acted as promoter for CO gas while inhibiter for NO 2 gas sensing due to their different sensing mechanisms. This study suggested that noble metals decoration of ZnO nanorods can be used for selectivity issue between CO and NO 2 gases.
TL;DR: In this paper, an optical temperature sensor based on the upconversion luminescence of Tm3+ has been developed for detecting temperature variations achieved better than previous reported rare earth ions fluorescence based temperature sensors.
Abstract: An optical temperature sensor based on the upconversion luminescence of Tm3+ has been developed. Under a 980 nm diode laser excitation, the fluorescence intensity ratio (FIR) between 700 (Tm3+:3F2,3 → 3H6) and 800 nm (Tm3+:3H4 → 3H6) upconversion emissions from Tm3+/Yb3+ codoped oxyfluoride glass ceramic was studied as a function of temperature in the range of 293–703 K. The 3F2,3 and 3H4 states of Tm3+ are verified to be thermally coupled levels. By using FIR technique, the sensitivity for detecting temperature variations achieved here is better than previous reported rare earth ions fluorescence based temperature sensors. With the advantages of intense upconversion luminescence and absolutely separated 700 and 800 nm emission bands, the Tm3+/Yb3+ codoped oxyfluoride glass ceramic is a very promising candidate for accurate optical temperature sensors with much higher sensitivity and resolution.
TL;DR: In this article, a gas sensor based on chemically reduced graphene oxide (CRG) by drop drying method was presented to create conductive networks between interdigitated electrode arrays, which is formed from the reduction of graphene oxide by p-phenylenediamine.
Abstract: a b s t r a c t We present a useful gas sensor based on chemically reduced graphene oxide (CRG) by drop drying method to create conductive networks between interdigitated electrode arrays. CRG, which is formed from the reduction of graphene oxide by p-phenylenediamine (PPD), can be used as an excellent sensing mate- rial. Its efficient dispersion in organic solvents (i.e., ethanol) benefits the formation of conductive circuits between electrode arrays through drop drying method. Preliminary results, which have been presented on the detection of dimethyl methylphosphonate (DMMP) using this simple and scalable fabrication method for practical devices, suggest that PPD reduced CRG exhibits much better (5.7 times with the concentration of DMMP at 30 ppm) response to DMMP than that of CRG reduced from hydrazine. Fur- thermore, this novel gas sensor based on CRG reduced from PPD shows excellent responsive repeatability to DMMP. Overall, the efficient dispersibility of CRG reduced from PPD in organic solvents facilitates the device fabrication through drop drying method, the resultant CRG-based sensing devices, with miniature, low cost, portable characteristics, as well as outstanding sensing performances, can ensure its potential application in gas sensing fields. © 2012 Elsevier B.V. All rights reserved.
TL;DR: In this paper, the authors examined the possibility of using aluminum nitride nanotubes (AlNNTs) as a potential gas sensor for HCOH detection by performing density functional theory (DFT) calculation.
Abstract: Semiconductive carbon nanotubes (CNTs) have demonstrated great sensitivity toward molecules such as NH3, NO, and NO2. Nevertheless, pristine CNTs cannot be used for detection of some highly toxic molecules such as formaldehyde (HCOH). In the present study, we examined the possibility of using aluminum nitride nanotubes (AlNNTs) as a potential gas sensor for HCOH detection by performing density functional theory (DFT) calculation. It was found that HCOH molecule can be chemisorbed on the surface of AlNNTs with Gibbs free energies of −0.59 to −0.64 eV, at standard temperature and pressure (STP, 1 atm and 298 K). In view of the high change of HOMO/LUMO energy gap of the tube during the chemisorption, it is expected that the process induce a significant change in its electrical conductivity. Hence, the AlNNT can be used as a potential efficient gas sensor for HCOH detection. Furthermore, it was shown that H2O molecules cannot significantly change the electronic properties of AlNNTs.
TL;DR: In this paper, a glucose sensor by modification of glassy carbon electrode (GCE) with graphene oxide (GO), NiO nanofibers (NiONFs) and Nation (NA) was presented.
Abstract: We present a glucose sensor by modification of glassy carbon electrode (GCE) with graphene oxide (GO), NiO nanofibers (NiONFs) and Nation (NA). NiONFs were prepared by the facile electrospinning technique followed by calcination. And GO was synthesized by Hummers method. The modified electrode was pretreated by the electrochemical reduction. The sensor was characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). The sensor exhibited high sensitivity (1100 mu AmM-1 cm(-2)), fast response time (less than 5 s), low detection limit of 0.77 mu M (S/N = 3), long term stability, and excellent anti-fouling ability for glucose determination. The sensor was further applied to detection of glucose in human blood serum sample, and the results accorded with those of commercial test. (C) 2012 Elsevier B.V. All rights reserved.
TL;DR: The limit of detection (LOD) and the sensitivity of a chemical sensor are defined using IUPAC guidelines using a simple statistical model implemented into a spreadsheet program.
Abstract: The limit of detection (LOD) and the sensitivity of a chemical sensor are defined using IUPAC guidelines. The LOD from simulated and experimental data is calculated from a calibration curve using a simple statistical model that was implemented into a spreadsheet program. This definition of the LOD is compared with the commonly used definition of the LOD, which is based on the product of sensitivity and the theoretical instrument resolution.
TL;DR: In this paper, a direct experimental comparison of the sensitivity and figure of merit of biosensors based either on surface plasmon polaritons on metal layers or on Bloch surface waves on one dimensional photonic crystals was conducted.
Abstract: We report on the direct experimental comparison of the sensitivity and figure of merit of biosensors based either on surface plasmon polaritons on metal layers or on Bloch surface waves on one dimensional photonic crystals. The comparison was carried out by making use of a commercial surface plasmon resonance platform that was slightly adapted for these experiments. Although the experimental conditions are not optimized for Bloch surface waves, our experiments demonstrate that both types of biosensors show a similar figure of merit for biochips deposited on low cost molded plastic substrates. For glass substrates with better optical quality, the increased homogeneity of the photonic crystals results in the Bloch surface wave sensors outperforming the surface plasmon polariton sensors by a factor 1.7 in terms of figure of merit. Considerations on the illumination bandwidth indicate options to further increase such a factor.
TL;DR: In this paper, a relative humidity fiber sensor based on Fabry-Perot interferometry configuration is presented, which is functionalized with a thin layer of a moisture-sensitive natural polymer chitosan to form a low fineness Fabry−Perot sensor.
Abstract: A relative humidity fiber sensor based on Fabry–Perot interferometry configuration is presented. The proposed fiber sensor is functionalized with a thin layer of a moisture-sensitive natural polymer chitosan to form a low fineness Fabry–Perot sensor. The sensing scheme used in this work is based on the swelling effect of chitosan sensing film (degree of swelling varies as a function of relative humidity) which will induce optical path modulation when relative humidity is changed. As observed, the proposed sensor exhibits a sensitivity of 0.13 nm/%RH for relative humidity ranging from 20%RH to 95%RH with a RH uncertainty of ±1.68%RH and fast response time of 380 ms.
TL;DR: In this paper, a 3D nanostructure in which flower-like microspheres consisting of SnO2 nanoflakes distributed among graphene oxide (GO) layers decorated with tiny SnCl2 nanoparticles, and was featured with high surface area (949 m2/g) with high response magnitude (159% for 50ppm NH3), fast response (response and recovery time), and high response time.
Abstract: SnO2/graphene (GN) composite was fabricated via a simple one-pot hydrothermal method with graphene oxide (GO) and SnCl2 as the precursors The composite was characterized by Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray diffraction patterns, scanning electron microscopy and high resolution transmittance electron microscopy It exhibited 3D nanostructure in which flower-like microspheres consisting of SnO2 nanoflakes distributed among GN layers decorated with tiny SnO2 nanoparticles, and was featured with high surface area (949 m2/g) GO is supposed to act as a template in the hydrothermal process, promoting the preferential growth of SnO2 nanocrystals and preventing the agglomeration of SnO2 nanoparticles NH3 sensing characteristics of the composite at room temperature were investigated, and found to closely relate to its composition and structure Under optimal conditions, the composite displayed high response magnitude (159% for 50 ppm NH3), fast response (response and recovery time
TL;DR: In this paper, a surface plasmon resonance based affinity biosensor comprising of 2S2G (Ge20Ga5Sb10S65) chalcogenide prism, graphene-multilayer and gold as a plasm active metal is proposed for sensing over a broad wavelength range in visible and near infrared regime.
Abstract: Surface plasmon resonance based affinity biosensor comprising of 2S2G (Ge20Ga5Sb10S65) chalcogenide prism, graphene-multilayer and gold as a plasmon active metal is proposed for sensing over a broad wavelength range in visible and near infrared regime. We have investigated and carried out detailed analysis to design high performance affinity biosensor by exploiting the unique optical properties of chalcogenide glass and graphene. The performance of the biosensor has been quantified in terms of sensitivity and detection accuracy. The sensitivity of proposed biosensor increases significantly due to the presence of graphene where as the detection accuracy increases by more than 100% because of high index chalcogenide glass as compared to silica glass. Also, the detection accuracy of the proposed sensor in near IR is 16 times more as compared to that in visible. Adequate values of crucial design parameters have been optimized to achieve the best possible sensing performance over a broad wavelength range.
TL;DR: From the experimental results, it is confirmed that the 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.
Abstract: 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 S 21 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 Δ f 1 p = 30 ± 2 MHz (for anti-PSA) and Δ f 1 c = 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.
TL;DR: In this article, three new chemodosimeters 1-3 were prepared, and their chromogenic and fluorogenic behaviors toward various anions were investigated, and the receptor 1 selectively exhibits a pronounced CN−-induced fluorescence enhancement.
Abstract: Three new chemodosimeters 1–3 were prepared, and their chromogenic and fluorogenic behaviors toward various anions were investigated. Receptors 1–3 show exclusive response toward CN− ion and also distinguish CN− from other anions by different color changes in aqueous solution (EtOH/H2O = 3/7, v/v). Among them, receptor 1 selectively exhibits a pronounced CN−-induced fluorescence enhancement. Thus, the receptor 1 can be used as a colorimetric and fluorescent sensor for the determination of CN− ion. The practical use of the receptor 1 for the determination of sodium cyanide (1.5 μM) in aqueous solution was also reported.
TL;DR: In this article, a modified carbon paste electrode with vinylferrocene/multiwall carbon nanotubes was fabricated and the electrochemical response of the modified electrode toward morphine was studied by means of cyclic voltammetry (CV), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS).
Abstract: A novel modified carbon paste electrode with vinylferrocene/multiwall carbon nanotubes was fabricated. The electrochemical response of the modified electrode toward morphine was studied by means of cyclic voltammetry (CV), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS). The structural morphology of the modified electrode was characterized by SEM technique. The prepared electrode showed an excellent electrocatalytic activity in the oxidation of morphine, leading to remarkable enhancements in the corresponding peak currents and lowering the peak potential. Using square wave voltammetry (SWV), we could measure morphine and diclofenac in one mixture independently from each other by a potential difference of about 300 mV for the first time. Square wave voltammetric peaks current of morphine and diclofenac increased linearly with their concentrations in the ranges of 0.2–250.0 μmol L −1 , and 5.0–600.0 μmol L −1 , respectively. The detection limits of 0.09 and 2.0 μmol L −1 were achieved for morphine and diclofenac, respectively. The proposed voltammetric sensor was successfully applied to the determination of morphine and diclofenac in real samples.
TL;DR: The fabrication, characterisation and the performance of a wearable, robust, flexible and disposable chemical barcode device based on a micro-fluidic platform that incorporates ionic liquid polymer gels (ionogels) is presented.
Abstract: This work presents the fabrication, characterisation and the performance of a wearable, robust, flexible and disposable chemical barcode device based on a micro-fluidic platform that incorporates ionic liquid polymer gels (ionogels). The device has been applied to the monitoring of the pH of sweat in real time during an exercise period. The device is an ideal wearable sensor for measuring the pH of sweat since it does not contain any electronic part for fluidic handle or pH detection and because it can be directly incorporated into clothing, head- or wristbands, which are in continuous contact with the skin. In addition, due to the micro-fluidic structure, fresh sweat is continuously passing through the sensing area providing the capability to perform continuous real time analysis. The approach presented here ensures immediate feedback regarding sweat composition. Sweat analysis is attractive for monitoring purposes as it can provide physiological information directly relevant to the health and performance of the wearer without the need for an invasive sampling approach.
TL;DR: In this paper, the authors synthesize one-dimensional nanostructures functionalized with Pd using a three-step process: thermal oxidation of Cu foil in air, dipping in a PdCl2 solution, and thermal annealing.
Abstract: CuO one-dimensional nanostructures functionalized with Pd were synthesized using a three-step process: thermal oxidation of Cu foil in air, dipping in a PdCl2 solution, and thermal annealing. The gas sensors fabricated from the multiple net worked Pd-functionalized CuO nanorods showed substantially enhanced electrical responses to H2S at 300 °C. The multiple networked CuO nanorod sensors showed a response of 400% at 100 ppm H2S at 300 °C, whereas the Pd-functionalized CuO nanorod sensors showed a response of 31,243% under the same conditions. The recovery time of the Pd-functionalized nanorod sensor is 5–8 times shorter than that of the bare–CuO nanorod, whereas the response time of the former was 2–3 times longer than that of the latter. In addition, the H2S gas sensing mechanism was examined, and the origin of the enhancement of the H2S gas sensing properties of the CuO nanorods by functionalization with Pd is discussed.
TL;DR: In this paper, a design of hierarchical SnO2/ZnO nanostructures for scalable fabrication of high-performance ethanol sensors is developed based on a combination of two simple synthesis pathways.
Abstract: Designing nanostructured materials to enhance gas-sensing performance is of important key for the next-generation sensor platforms In this paper, a design of hierarchical SnO2/ZnO nanostructures for scalable fabrication of high-performance ethanol sensors is developed based on a combination of two simple synthesis pathways High-quality single crystalline SnO2 nanowire (NW) backbones were first synthesized using the thermal evaporation method, whereas ZnO nanorod (NR) branches were subsequently grown perpendicularly to the axis of SnO2 NWs via the hydrothermal approach The successful synthesis of SnO2/ZnO hierarchical nanostructures is confirmed by the results of scanning electron microscope, X-ray diffraction and photoluminescence spectrum The ethanol-sensing properties of the SnO2/ZnO hierarchical nanostructures sensors were systematically investigated and compared to those of the bare SnO2 NWs sensor The effect of growth manipulation of the SnO2/ZnO hierarchical nanostructures on the ethanol sensing characteristics was also studied The results revealed that the design of the hierarchical nanostructures enhanced the ethanol gas response and selectivity for interfering gases such as NH3, CO, H2, CO2, and LPG These enhancements are attributed to the enhancement of homogenous and heterogeneous NW–NW contacts In addition, the results of this study may serve as a basis for designing various novel hierarchical nanostructures for other applications, including photocatalysis, battery electrode, solar cell, and nanosensors
TL;DR: In this paper, a nonenzymatic, amperometric sensor for hydrogen peroxide (H2O2) was developed based on an electrochemically prepared reduced graphene oxide (RGO)/zinc oxide (ZnO) composite using a simple and cost effective approach.
Abstract: A novel nonenzymatic, amperometric sensor for hydrogen peroxide (H2O2) was developed based on an electrochemically prepared reduced graphene oxide (RGO)/zinc oxide (ZnO) composite using a simple and cost effective approach. RGO/ZnO composite was fabricated on a glassy carbon electrode (GCE) by a green route based on simultaneous electrodeposition of ZnO and electrochemical reduction of graphene oxide (GO). The morphology of the as-prepared RGO/ZnO composite was investigated by scanning electron microscopy (SEM). Attenuated total reflectance (ATR) spectroscopy has also been performed to confirm the ample reduction of oxygen functionalities located at graphene oxide (GO). The electrochemical performance of the RGO/ZnO composite modified GCE was studied by amperometric technique, and the resulting electrode displays excellent performance towards hydrogen peroxide (H2O2) at −0.38 V in the linear response range from 0.02 to 22.48 μM, with a correlation coefficient of 0.9951 and short response time (<5 s). The proposed sensor also has good operational and storage stability with appreciable anti-interferring ability.
TL;DR: In this paper, a spin-coating method was used to use graphene oxide-silicon bi-layer flexible structure as stress-based humidity sensors, and the results show that the structure exhibits high humidity sensitivity, good repeatability, small humidity hysteresis and clear and fast response-recovery.
Abstract: In this work, we present an approach to use graphene oxide-silicon bi-layer flexible structure as stress-based humidity sensors. By the spin-coating method, graphene oxide thin films were deposited onto silicon microbridge as a humidity sensing layer. Upon expose to humid environment, graphene oxide thin films swells and leads to the bending of silicon membrane. Then, the full piezoresistive Wheatstone-bridge embedded in silicon microbridge was used to transform the deformation into a measurable output voltage. The humidity sensing properties of the bi-layer flexible structure, such as sensitivity, repeatability, humidity hysteresis, response and recovery, were investigated in the wide relative humidity range of 10–98%. The test results show that graphene oxide-silicon bi-layer flexible structure exhibits high humidity sensitivity, good repeatability, small humidity hysteresis and clear and fast response–recovery. Moreover, the dependence of the thin films thickness of graphene oxide on the response properties was also examined. At last, the humidity sensing mechanism of the proposed bi-layer structure was discussed in detail.
TL;DR: In this article, the relationship between apparent enzyme kinetic parameters and nanomaterials structure is investigated in order to rationally design the catalytic activity of the Au nanorods.
Abstract: Au nanorods @ Pt nanodots core/shell nanostructures, prepared by the Au nanorods (NRs)-mediated growth, exhibit dual functional enzyme-like (peroxidase and oxidase-like) activities. From the viewpoint of enzyme mimics, the relationship between apparent enzyme kinetic parameters and nanomaterials structure is investigated in order to rationally design the catalytic activity. Using peroxidase-like properties of the Au@Pt NRs, the determination of hydrogen peroxide (H2O2) was demonstrated with a limit of detection (LOD) of 4.5 × 10−5 M and a linear range of 4.5 × 10−5–1 × 10−3 M using o-phenylenediamine (OPD) as chromogenic substrate. Furthermore, in combination with highly specific reactions provided by natural enzymes, selective detections of glucose and lipophilic cholesterol were demonstrated with similar LODs and linear ranges. Additionally, owing to the specific oxidase-like activity of the Au@Pt NRs (ascorbate oxidase), interference of ascorbic acid in the detection of glucose could be eliminated. In conclusion, considering the flexibility in the design of nanomatererials, there is a lot of space to improve their activity and explore their potential applications, especially in relatively harsh conditions.