基于SnO2-CuO纳米纤维的薄膜型H2-S传感器研究

采用同轴静电纺丝技术制备了SnO2-CuO复合纳米纤维,采用提拉法将SnO2-CuO纳米纤维涂覆于印有梳状Au电极的氧化铝陶瓷管表面形成敏感薄膜,设计了一种新型薄膜式H2 S传感器。采用 X 射线衍射、扫描电子显微镜和X-射线光电子能谱( XPS)表征SnO2-CuO纳米纤维的相组成和微观形貌,分析了敏感薄膜成分配比和厚度对硫化氢敏感机理和电化学特性。采用WS-30A型气敏元件分析仪测试了H2 S传感器敏感特性、温度特性、湿度特性、动态响应、抗干扰特性和稳定性。结果表明,以C50纳米纤维为敏感薄膜(膜厚为70 nm)的H2 S传感器,在温度为25℃, H2 S气体浓度为10~60 mg/L时,传感器线性度和灵敏度分别为92.3％和98.2％,响应最大值为1080,承受的最大相对湿度为95％,动态响应和恢复时间分别为4和12 s。此传感器对CO, NO2, SO2, NH3, CO2, CH4和H2等有害气体具有较好的抗干扰性。在矿井中连续使用12月后,响应衰减了9.2％,响应正常时间为10.9月。     

Demonstration of a simple, economical and practical technique utilising an imprinted polymer for metal ion sensing

This paper describes a simple, economical and practical optical sensor that has been developed using an ion imprinted polymer for detecting copper(II) ion using reflectance spectrometry. The imprinted polymer was synthesised in the presence of copper(II) ion using 4-vinylpyridine as monomer, 2-hydroxyethyl methacrylate as co-monomer, and ethylene glycol dimethacrylate as cross-linker in methanol via free radical polymerisation. The polymer formed was physically ground into fine particles, fabricated into a sensor probe and attached at the tip of an optical fibre bundle. The sensor operates optimally at pH 5 under constant stirring condition and has a linear dynamic range for copper(II) ion determination of 0.4–4.0 mM. The limit of detection for the sensor was 123 µM. The sensor has high selectivity for monitoring copper (II) ion in a multi-analyte environment, while also exhibiting better sensitivity compared to non-imprinted polymer. The response of the sensor can be regenerated fully without significant loss in its analytical signal for re-use. This reduces the consumable cost and at the same time making the operational process of such sensor simpler and more practical to be employed in real applications.     

As(III) Voltammetric Detection by Means of Disposable Screen‐Printed Gold Electrochemical Sensors

Abstract

In this paper a disposable gold screen‐printed working electrode was tested for arsenic detection in aqueous solutions using Square Wave Anodic Stripping Voltammetry (SWASV). The dynamic range of the sensor and its response were characterised in standard As(III) solutions; particular efforts were devoted to optimize electrode surface conditioning and electrolyte solution composition. The detection limit was 2.5 µg l^?1 using 60 s as deposition time. A portable battery‐operated device was used to demonstrate the possibility to use the sensor for on‐site analysis. Analysis of spiked samples was also performed.     

Dynamic response characteristics of the potentiometric carbon dioxide sensor for the determination of aspartame

The dynamic response characteristics of a carbon dioxide gas sensor were studied to determine the potential for application of the device to the kinetic assay of substrate(s) under pseudo first-order kinetics. The dependence of the time constant on the concentration of carbon dioxide was determined by using convolution mathematics to analyse potentiometric changes caused by abrupt alterations of gas concentration. The operational conditions of the CO2 sensor were optimised for the development of enzyme electrodes, so that the mass-transport phenomena occurring during the course of the enzymic reactions were enhanced. As a result, the kinetic analysis of substrate(s) was performed more rapidly (2-6 min), with greater sensitivity and with an improved detection limit (10-5 M). A kinetic reaction-rate method for the determination of aspartame in dietary foodstuffs is proposed as a rapid and inexpensive alternative to a classical high-performance liquid chromatographic method.     

Distinction of gases with a semiconductor sensor depending on the scanning profile of a cyclic temperature

A gas-sensing system based on a dynamic nonlinear response is reported to improve the selectivity in the sensor response toward sample gases. A cyclic temperature composed of fundamental and second harmonics was applied to a SnO(2) semiconductor gas sensor and the resulting conductance of the sensor was analyzed by fast Fourier transformation (FFT). The dynamic nonlinear responses to the gas species were further characterized depending on the scanning profile of the temperature. These characteristic sensor responses under the application of second-harmonic perturbation were theoretically considered based on a reaction-diffusion model for the semiconductor surface.     

Virtual sensor array as a tool for classifying air pollution

This work examined the acquisition of information about gases using a virtual sensor array and classification. We were particularly interested in the approach in which classes are defined in a qualitative–quantitative manner, that is, by identifying the gas and concentration range. This type of information will be of interest for air pollution assessment purposes. In this field of application, it is often not necessary to provide very precise information. The idea of the virtual sensor array exploits the dependence of a gas sensor’s response on operating conditions. Originally it was developed as a means to improve the selectivity of an electronic nose when energy consumption by this device was a serious limitation. If the response of one sensor is measured in n time points, and each time point is characterised by different controlled exposure conditions, the sensor becomes analogous to an n-dimensional virtual sensor array. Compared with conventional approaches, a virtual sensor array based on a single sensor offers low power consumption, low volume, and low cost, which opens up new markets for wide application of portable and handheld devices. In this article, we show that a virtual sensor array and classification may serve as a reliable source of qualitative–quantitative information about gases. Twenty-six classes (five substances, each at five concentration ranges, and pure air) were recognised with a true positive rate higher than 99.14 ± 0.49% and a true negative rate higher than 99.21 ± 0.52%. As demonstrated, the basis for recognition could be a virtual sensor array associated with a low-power consuming sensor (210–280 mW). The complexity of the applied classifier could be adjusted depending on the choice of sensor operating conditions. For a complex classifier like support vector machine, dynamic exposure was sufficient to obtain high classification performance. A simpler classifier like k-nearest neighbours required more information, that is, information associated with static as well as dynamic exposure.     

Distinguishing Among Gases with a Semiconductor Sensor Depending on the Frequency Modulation of a Cyclic Temperature

A gas‐sensing system based on a dynamic nonlinear response shows enhanced selectivity of the sensor response toward sample vapors. A cyclic temperature composed of fundamental and 1.5‐th harmonics was applied to a SnO₂ semiconductor gas sensor and the resulting conductance of the sensor was evaluated by a polynomial approximation. The dynamic nonlinear responses to the samples were further characterized by the addition of 1.5‐th harmonic perturbation as a frequency modulation. These characteristic sensor responses under frequency modulation were considered theoretically based on a reaction‐diffusion model for the semiconductor surface.     

Cu2+‐doped ITO as a Novel Efficient,Transparent, and Fast‐Response Transducer for Ammonia Sensing

As a novel approach, the effect of Cu²⁺‐doped indium tin oxide (ITO) on a flexible polycarbonate substrate is considered as an ammonia sensor. The sensor was fabricated using spin‐coating and subsequent annealing at 160°C for 60 min. The constructed sensor morphology accomplished by surface composition was explored using scanning electron microscopy (SEM) and energy dispersiveX‐ray (EDX) spectroscopy. Using the new strategy, a flexible sensor for ammonia determination with a fast response time of less than 7 s and a recovery time of 8 s was achieved. Sensor characteristics, such as sensitivity, recyclability, response/recovery time, selectivity, stability, flexibility, and transmittance of the layers, were examined. The impedance results showed high sensitivity when the constructed sensor was exposed to NH₃ concentrations in the range 5–1000 ppm. The results showed that doping ITO with Cu²⁺ imparted higher electronic charge density to the sensor surface and enhanced the sensitivity of the sensor by a factor of 352% in comparison with that of pure ITO. The sensitivity, fast response, and recovery time with low‐cost materials and deposition procedure suggest an effective and disposable ammonia sensor at room temperature (23°C).     

Polydopamine-modified MWCNTs-glassy Carbon Electrode,a Selective Electrochemical Morphine Sensor

An electrochemical sensor based on a glassy carbon electrode was prepared using f-MWCNTs and polydopamine. Several techniques were used to investigate the surface features. Voltammetric techniques were used to evaluate the electrocatalyst efficiency, and it was used for morphine determination using differential pulse voltammetry. Different parameters affecting the method‘s sensitivity and selectivity were optimized. The linear dynamic range was 0.075–75.0 μM with a detection limit of 0.06 μM morphine. Also, the method‘s selectivity was tested, which was proved to be satisfactory. Finally, the sensor was successfully used for morphine determination in human plasma and urine samples with acceptable results.     

Quantitative analysis of NO2 in the presence of CO using a single tungsten oxide semiconductor sensor and dynamic signal processing

We demonstrate that NO2 can be quantitatively analysed in the presence of CO using a single tungsten oxide based resistive gas sensor. The working temperature of the sensor was modulated between 190 and 380 degrees C and its dynamic response to different concentrations of CO, NO2, and CO + NO2 mixtures was monitored. Either the fast Fourier transform (FFT) or the discrete wavelet transform (DWT) was used to extract important features from the sensor response. These features were then input to different (statistical and neural) pattern recognition methods. The species considered can be discriminated with a success rate higher than 90% using a Fuzzy ARTMAP or a radial basis function neural network. The concentrations of the gases studied can be accurately predicted, by using the DWT coupled to partial least squares (PLS) models. The correlation coefficients of the predicted versus real concentrations were 0.923, 0.870 and 0.866 for CO, NO2, and NO2 in CO + NO2 mixtures, respectively.     

The Ag(s)/AgI(s)/graphite solid cell as iodine sensor: speed of response and use of Cs-doped AgI as electrolyte

The time response of a Ag(s)/AgI(s)/graphite(s), I₂(g) galvanic cell as iodine sensor was studied using both pure AgI and CsI doped AgI as electrolyte. The use of doped silver iodide expanded considerably the working temperature. An analytical modeling of the sensor response is presented. Electronic Publication     

Development of a diamine biosensor

An amperometric diamine sensor is developed for clinical applications in diagnosis of bacterial vaginosis (BV). The sensor is based on crosslinked putrescine oxidase (PUO) which catalyzes the conversion of diamines (mainly putrescine and cadaverine) to products including hydrogen peroxide. The hydrogen peroxide is detected anodically at platinum electrode polarized at 0.5 V versus Ag/AgCl. Platinum-plated gold electrodes used as a substrate for the sensor construction, are batch-fabricated on a flexible polyimide foil (Kapton(R), DuPont). A three-electrode cell configuration is used in all amperometric measurements. The sensor construction is based on three layers: an inner layer to reject the interference effect of oxidizable molecules, an outer diffusion controlling layer, and in addition, an enzyme middle layer. The enzyme layer was immobilized by crosslinking PUO with bovine serum albumin (BSA) using glutaraldehyde (GA). An optimization study of the enzyme solution composition was carried out. With the optimized enzyme layer, the biosensor showed a very high sensitivity and fast response time of ca. 20 s. The sensor has a linear dynamic range from (0.5-300 muM) for putrescine that covers the expected biological levels of the analyte. Details on sensor fabrication and characterization are given in the present work.     

Electrical and humidity characterization of m-NA doped Au/PVA nanocomposites

The Meta-Nitroaniline (m-NA) doped (by varying weight percentage (wt. %)) gold/polyvinyl alcohol (Au/PVA) nanocomposites were synthesized using gold salt and hydrazine hydrate (HH) by in situ process. The composite was coated on ceramic rods having two end electrodes by drop casting method for studying their electrical behavior at different relative humidity (RH) levels, ranging from 4 to 95% RH at room temperature. The optimized wt. % was used to prepare coatings of various thicknesses (20-40 μm) of the films. As the humidity decreases, the resistance increases. The low humidity sensing characteristic can be tailored by varying wt. % of m-NA and thicknesses of the nanocomposite films. The resistive-humidity sensor shows two regions of sensitivity having highest sensitivity for lower RH. The sensor response and recovery time is about 6-10 s and 52 s respectively. The dynamic range of variation of the resistance allows a promising use of the films as a humidity sensor. The material was characterized by X-ray diffraction (XRD) and impedance spectroscopy at 60% RH.     

A sensitive enzymeless hydrogen-peroxide sensor based on epitaxially-grown Fe3O4 thin film

A novel and facile approach has been developed to synthesize thin films of magnetite (Fe(3)O(4)) with epitaxial needle-like columnar grains on titanium nitride (TiN) buffered substrate using DC magnetron reactive sputtering. TiN buffer layer was first sputtered onto a substrate at 550 °C as a preferable substrate for growth following sputtering of epitaxial crystalline Fe(3)O(4) at 300 °C. The as-synthesized epitaxial Fe(3)O(4) was extensively characterized. The electrocatalytic activity of the epitaxial Fe(3)O(4) thin-film sensor against hydrogen peroxide (H(2)O(2)) reduction was rapid with a response time less than 5 s. The sensor also exhibited an acceptable stability, a satisfying sensitivity of 432.2 μA mM(-1) cm(-2), good specificity to the substrate, a dynamic working range of up to 0.7 mM and a low detection limit of 1.0 μM. The sensor performance correlated well (R(2)=0.996) with results obtained using a commercial HPLC-UV device. The sensor performance was robust and accurate in measuring H(2)O(2) in some complex matrices. The advantages of relative simplicity and ease of mass production make the epitaxial Fe(3)O(4) thin film promising candidate for use in sensing applications.     

A gas sensor based on Prussian blue film for the detection of chlorobenzene vapor

A new resistance-type sensor based on Prussian blue film has been fabricated for the detection of chlorobenzene vapor. The effect of Prussian blue preparation conditions on the response of sensor was studied. The sensor exhibited good response and selectivity to chlorobenzene vapor. The sensor prepared with Fe₂(SO₄)₃ at 298 K has response 8.5 at operating voltage of 10 V. The selectivity of the sensor to chlorobenzene against all other tested gases is exceeding almost by 5.6 times. The sensor showed linear response to chlorobenzene vapor in the concentration range of 24–169 ppm at room temperature and at a 10 V operating voltage. The response and recovery time of the sensor was about 18 and 12 s, respectively. Sensor stability test indicated the sensor had a good stability. Furthermore, seven real samples of chlorobenzene vapor was measured using the sensor. The relative error was in the range of about ±1.3%.     

Evaluation of the responses of a semiconductor gas sensor to gaseous mixtures under the application of temperature modulation

A novel gas-sensing system based on a dynamic nonlinear response is reported to evaluate the effect of gaseous mixtures on the sensor response. A sinusoidal temperature perturbation was applied to a semiconductor gas sensor and the resulting conductance of the sensor was analyzed by fast Fourier transformation (FFT). The sensor response, which changed characteristically depending on the composition of the gaseous mixture, could be classified into three types (enhanced, suppressed, and preferential responses) by the mixture. To monitor the progress of the reaction of gases, the sample gas was analyzed by gas chromatography. The coexistent effect on the response to gaseous mixtures was theoretically simulated by considering the kinetics of gas molecules on the semiconductor surface.     

A Novel Microbial Sensor for Anionic Surfactant Determination

Abstract

A novel whole cell biosensor was constructed for detection of anionic surfactants in an aquatic environment. The sensor response to linear alkyl benzene sulfonates was linear up to 6 mg l^?1 which is a range suitable for the detection of anionic surfactant concentration in polluted river water. Under optimum conditions, the sensor response time was less than 15 min. Anionic surfactant analysis was rapid and convenient and did not require organic reagents which are harmful to an environment.     

High Selective Parathion Voltammetric Sensor Development by Using an Acrylic Based Molecularly Imprinted Polymer‐Carbon Paste Electrode

The design and construction of an extra high selective voltammetric sensor for parathion by using a molecularly imprinted polymer (MIP) as recognition element was introduced. A parathion selective MIP and a nonimprinted polymer (NIP) were synthesized and then incorporated in the carbon paste electrode. The MIP‐CP electrode showed very high recognition ability in comparison to NIP‐CP. It was shown that electrode washing after parathion extraction, led to enhanced selectivity. Some parameters affecting the sensor response were optimized and then the calibration curve was plotted. A dynamic linear range of 1.7–900 nM was obtained. The detection limit of the sensor was calculated as 0.5 nM. This sensor was used successfully for parathion determination in real samples such as ground water and vegetables.     

New analysis of clopidogrel bisulfate in plavix tablet and human biological fluids utilizing chemically modified carbon paste sensor

The fabrication and the performance response characteristics of a sensitive, selective, simple, and rapid sensor for the determination of clopidogrel bisulfate (CLO-H₂SO₄) were described. The constructed carbon paste sensor comprised of an ion-pair based on clopidogrel with silicotungstate (CLO-ST) where this study included: composition, usable pH range, response time and temperature. The sensor exhibited a wide linear dynamic concentration ranging from 1.00 × 10⁻⁷ to 1.00 × 10⁻² and the usable pH ranges from 1.2 to 4.8 with the response time ranging from 5 to 8 s which is much faster compared to liquid ISEs with a detection limit equalling 0.34 nM. The selectivity of the sensor (CLO-H₂SO₄) was applied with respect to many of organic and inorganic cations, amino acids and sugars. The sensor had applications in bulk powder, tablets, humans (serum-urine) and in monitoring Plavix tablets’ dissolution rates. The obtained results were statistically analyzed for both accuracy and precision and were compared using the US pharmacopeial method where no significant difference was observed.     

A biocompatible needle-type glucose sensor based on platinum-electroplated carbon electrode

A biocompatible needle-type glucose sensor with a 3-electrode configuration was constructed. A platinum-electroplated carbon stick was used as the working electrode, Ag/AgCl as the reference electrode, and a disposable hypodermic needle made of stainless steel as the counter electrode. A Nafion membrane, an immobilized glucose oxidase (GOD) membrane, and a biocompatible membrane with diffusion-limiting effect were coated successively onto the working electrode. The sensor showed a rapid response (< 120 s in batch operation), good reproducibility (RE < 3%), good stability (over 36 h in control serum), a wide dynamic range (5-600 mg/dL glucose), and superior biocompatibility. It was used to determine glucose in serum. The data obtained from the sensor showed good agreement with that from a clinical autoanalyzer (R > 0.95).