Nanocrystalline graphite-like pyrolytic carbon film electrode for electrochemical sensing of hydrazine

Pyrolytic carbon film (PCF) electrode fabricated by a non-catalytic chemical vapor deposition (CVD) process was used as an electrochemical sensor for the detection of hydrazine. The electrode response was found to be electrocatalytic producing a reduction in the overpotential compared to other unmodified carbon-based electrodes such as glassy carbon (GC), basal-plane pyrolytic graphite (BPPG), and edge-plane pyrolytic graphite (EPPG) electrodes. The overall number of electrons involved in the electro-oxidation of hydrazine, the number of electrons involved in the rate-determining step, and diffusion coefficient of hydrazine at PCF electrode were estimated using cyclic voltammetry and chronoamperometry. The performance of PCF electrode was comparable to and in some cases even better than many chemically modified electrodes in terms of detection limit, linear dynamic range, and sensitivity. Moreover, the sensor exhibited fast response time (within 2 s), high response stability, and reproducibility. All the results indicated this sensor is suitable for hydrazine analysis.     

A sensitive hydrazine electrochemical sensor based on electrodeposition of gold nanoparticles on choline film modified glassy carbon electrode

A highly sensitive hydrazine sensor was developed based on the electrodeposition of gold nanoparticles onto the choline film modified glassy carbon electrode (GNPs/Ch/GCE). The electrochemical experiments showed that the GNPs/Ch film exhibited a distinctly higher activity for the electro-oxidation of hydrazine than GNPs with 3.4-fold enhancement of peak current. The kinetic parameters such as the electron transfer coefficient (α) and the rate of electron exchange (k) for the oxidation of hydrazine were determined. The diffusion coefficient (D) of hydrazine in solution was also calculated by chronoamperometry. The sensor exhibited two wide linear ranges of 5.0 × 10⁻⁷-5.0 × 10⁻⁴ and 5.0 × 10⁻⁴-9.3 × 10⁻³ M with the detection limit of 1.0 × 10⁻⁷ M (s/n = 3). The proposed electrode presented excellent operational and storage stability for the determination of hydrazine. Moreover, the sensor showed outstanding sensitivity, selectivity and reproducibility properties. All the results indicated a good potential application of this sensor in the detection of hydrazine.     

Label-free electrochemical immunosensor for sensitive detection of kanamycin

A novel label-free electrochemical immunosensor for sensitive detection of kanamycin based on water-soluble graphene sheet (WGS)/prussian blue-chitosan (PB-CTS)/nanoporous gold (NPG) composited film has been reported. PB was selected as an electron transfer mediator, and was modified onto the electrode together with WGS through electrostatic adsorption. Then NPG was immobilized onto the as-prepared film for biomolecules anchoring. The electroactivity of PB was greatly enhanced in the presence of WGS and NPG. It could mainly be ascribed to the fact that the good conductivity of WGS and NPG promoted electron transfer and enhanced the sensitivity. kanamycin antibody, as a model, was immobilized onto the composite film for the detection of kanamycin. Under optimum conditions, the amperometric signal of PB decreased linearly with kanamycin concentration (0.02-14 ng mL⁻¹), a linear calibration plot (y = 1.3817 + 4.7544x, r = 0.9993), resulting in a low limit of detection (6.31 pg mL⁻¹). The novel immunosensor for the detection of kanamycin in real sample with satisfactory results has been proved. In addition, this method would be easily adapted for the detection of other residual antibiotics in animal derived foods.     

Large-area interdigitated array microelectrodes for electrochemical sensing

Advanced photolithography developed for the semiconductor industry has been used to fabricate interdigitated microelectrode arrays that pass steady-state limiting currents of up to 230 nA/μM analyte — 2.5 times more than the most sensitive interdigitated array built to date, and exhibit response times of ∼5 ms. This performance results from the small interelectrode gap and the large active area of the device (4 mm²), a combination enabled by advanced photolithography. We describe the fabrication of these arrays and the characterization of their performance in two environments: an aqueous solution of Ru(NH₃)₆³⁺ and a dinitrotoluene solution in acetonitrile. The scaling of array performance parameters with device dimensions is also presented.     

Ethanol sensing using CuO/MWNT thin film

Copper (II) oxide (CuO)/multiwall carbon nanotube (MWNT) thin film based ethanol-sensors were fabricated by dispersing CVD-prepared MWNTs in varying concentration over DC magnetron sputtered-CuO films. The responses of these sensors as a function of MWNT concentrations and temperatures were measured, and compared. The sensing response was the maximum at an operating temperature near 400 °C for all the samples irrespective of the MWNTs dispersed over them. At optimum operating temperature (T_opt) of 407 ± 1 °C, the response is linear for 100-700 ppm range and tends to saturate at higher concentrations. In comparison with bare CuO sample, the response of CuO/MWNT sensing films increased up to 50% in the linear range. The response improvement for 2500 ppm of ethanol was up to 90% compared to bare CuO sample. In addition, the sensing response time also reduced to around 23% for lowest ethanol concentration at T_opt. However, a decrease in the sensor response was observed on films with very high concentrations of MWNTs.     

Integrated microfluidic system for electrochemical sensing of glycosylated hemoglobin

This article reports a new miniature electrochemical detection system integrating a sample pretreatment device for fast detection of glycosylated hemoglobin (HbA_1C), which is a common indicator for diabetes mellitus. In this system, circular micropumps, normally closed microvalves, dielectrophoretic (DEP) electrodes, and electrochemical sensing electrode are integrated to perform several crucial processes. These processes include separation of red blood cells (RBCs), sample/reagent transportation, mixing, cell lysis, and electrochemical sensing. For the HbA_1C measurement, the RBCs are separated and are collected from whole human blood by using a positive DEP force generated by the DEP electrodes. The collected RBCs are then lysed to release HbA_1C for the subsequent electrochemical detection processes. Experimental data show that the RBCs are successfully separated and are collected using the developed system with a RBCs capture rate of 84.2%. The subsequent detection of HbA_1C is automatically completed by utilizing electrochemical sensing electrode. The microfluidic system only consumes a sample volume of 200 μl. The entire process is automatically performed within a short period of time (10 min). The development of this integrated microfluidic system may be promising for the clinical monitoring of diabetes mellitus.     

Low power highly sensitive platform for gas sensing application

This paper reports a low power miniaturized MEMS based integrated gas sensor with 36.84 % sensitivity (ΔR/R₀) for as low as 4 ppm (NH₃) gas concentration. Micro-heater based gas sensor device presented here consumes very low power (360 °C at 98 mW/mm²) with platinum (Pt) micro-heater. Low powered micro-heater is an essential component of the metal oxide based gas sensors which are portable and battery operated. These micro-heaters usually cover less than 5 % of the gas sensor chip area but they need to be thermally isolated from substrate, to reduce thermal losses. This paper elaborates on design aspects of micro fabricated low power gas sensor which includes ‘membrane design’ below the microheater; the ‘cavity-to-active area ratio’; effect of silicon thickness below the silicon dioxide membrane; etc. using FEM simulations and experimentation. The key issues pertaining to process modules like fragile wafer handling after bulk micro-machining; lift-off of platinum and sensing films for the realization of heater, inter-digitated-electrodes (IDE) and sensing film are dealt with in detail. Low power platinum microheater achieving 700 °C at 267 mW/mm² are fabricated. Temperature calculations are based on experimentally calculated thermal coefficient of resistance (TCR) and IR imaging. Temperature uniformity and localized heating is verified with infrared imaging. Reliability tests of the heater device show their ruggedness and repeatability. Stable heater temperature with standard deviation (σ) of 0.015 obtained during continuous powering for an hour. Cyclic ON–OFF test on the device indicate the ruggedness of the micro-heater. High sensitivity of the device for was observed for ammonia (NH₃), resulting in 40 % response for ~4 ppm gas concentration at 230 °C operating temperature.     

A nano-copper electrochemical sensor for sensitive detection of chemical oxygen demand

Copper nanoparticle (nano-Cu) was electrodeposited on the surface of Cu disk electrode under −1 V for 60 s, and then used to construct an electrochemical sensor for chemical oxygen demand (COD). The electrochemical oxidation behavior of glycine, a standard compound for evaluating the COD, was investigated. The potential shifts negatively, and the current increases greatly at the surface of nano-Cu, indicating remarkable enhancement effect on the detection of COD. The analytical conditions such as electrolyte, deposition potential, deposition time and detected potential were studied. As a result, a sensitive, simple and rapid electroanalytical method was developed for COD using amperometric detection. The linear range is from 4.8 to 600 mg L⁻¹, and the limit of detection is as low as 3.6 mg L⁻¹. Moreover, this method exhibits high tolerance level to chloride ion, and 0.02 M chloride ion has no influence. Finally, the sensor was used to detect the COD values of different water samples, and the results were testified by the standard dichromate method.     

A simple polymer based electrochemical transistor for micromolar glucose sensing

A simple and inexpensive glucose sensor with micromolar sensitivity is demonstrated. The sensor utilizes a poly(3,4-ethyelenedioxythiphene) poly(styrene sulfonate) (PEDOT:PSS) based electrochemical transistor in which all the electrodes and the channel were made with the same polymer. The sensor was fabricated in a one step fabrication process using inexpensive and rapid xurography technique and is able to detect glucose concentrations from approximately 1 μM to 10 mM and showed adequate change for glucose levels in the range of human saliva (8-210 μM) without utilizing any external electron mediators.     

智能移动设备在电化学检测分析中的应用

智能移动设备近年来发展迅速,市场占有率急剧增长。面向不同研究领域,与多种传感技术相结合的移动检测系统常见诸报道。该文综述了智能移动设备硬件和软件的迅速发展,以及为了满足日益增长的移动分析检测需求所开发的基于智能移动设备的分析检测方法,特别是智能移动设备在电化学检测分析中的应用。     

低成本高分辨率电化学传感技术测量大气N_O

为解决三电极电化学传感器分辨率过低、光学探测仪器成本高昂的困扰,设计了以STM32为核心的NO_2电化学传感器监测系统,利用低成本高分辨率电化学传感技术测量大气中NO_2的体积分数。实验表明:-10～10℃时传感器响应时间T90受温度影响严重,传感器灵敏度温度特性曲线S (T)=0. 197 60+0. 002 13T-0. 001 21T2(-10℃相似文献   

电化学CO气体传感器及其敏感特性

介绍了电化学CO气体传感器的结构,辅助电极、Ag/AgCl参比电极的制作以及工作电极的修饰和制作方法,研究了该传感器对CO气体的敏感特性。实验结果显示:活化处理后的Pt溶胶修饰的Pt丝微电极对CO气体有良好的敏感特性,CO氧化峰尖锐、峰形良好,在低浓度范围内,其峰电流与CO的浓度成良好的线性关系,表明此传感器适于定量检测CO的浓度。     

Growth and gas sensing characteristics of p- and n-type ZnO nanostructures

ZnO nanoparticles (NPs) of 5-15 nm size and nanowires (NWs) of 50-100 nm dia., exhibiting p and n-type characteristics, respectively, have been synthesized using simple chemical process. ZnO NW-films exhibited good sensitivity and selectivity towards H₂S in ppm range with fast response and recovery times. Interestingly, ZnO NP-films showed p-type conductivity that has been obtained for the first time without intentional doping while NW-films showed n-type conduction as has also been reported in various earlier studies. The p- and n-type conductivities in NP- and NW-films have been confirmed using hot probe and Kelvin probe measurements. The n-type behavior of NW-films is attributed to oxygen vacancies, whereas the p-type nature of NP-films is attributed to the zinc vacancy, surface acceptor levels created by the adsorbed oxygen and/or the unintentional carbon doping in ZnO.     

Gas sensing properties of CuO nanorods synthesized by a microwave-assisted hydrothermal method

P-type CuO nanorods with the breadth of 15-20 nm and the length of 60-80 nm, have been synthesized using a microwave-assisted hydrothermal (MH) method. The band gap of CuO nanorods was calculated to be 2.75 eV based on the UV-vis absorption spectrum of the product. The gas sensing property of the CuO nanorods to several organic vapors was tested in temperatures ranging from 160 °C to 300 °C. The response of the CuO sensor to ethanol (1000 ppm) was 9.8 at the working temperature of 210 °C. The response time and the recovery time were within the range of 13-42 s and 17-51 s, respectively. Further measurements exhibited stronger response to ethanol than to other target gases. The enhanced gas sensing performance of the sensor to ethanol may be attributed to the small size of the CuO particles.     

Platelet graphite nanofibers/soft polymer composites for electrochemical sensing and biosensing

The fabrication and attractive sensing and biosensing performance of platelet graphite nanofibers/polysulfone (PGNF/PSf) composite nanomaterials is described. The PGNF/PSf nanocomposites were fabricated by facile phase-inversion method. Their electrochemical performance was compared to the one of carbon nanotubes/PSf and graphite microparticles/PSf composite. It was clearly demonstrated that PGNF/PSf provides superior voltammetric and amperometric performance for sensing and biosensing over those two other sp² carbon materials. This can be attributed to the unparallel amount of electroactive edge sites on PGNF in which electroactivity is not impaired by the polysulfone binder. PGNF/PSf/glucose oxidase nanobiocomposite was prepared and used for proof-of-concept biosensing of glucose.     

电化学WO_3基乙醇气敏元件的研制

在WO3粉体材料中加入一定质量比的添加剂,于恒温600℃烧结1h制成旁热式厚膜乙醇气敏元件。采用静态电压测量法,研究了元件的加热电压与元件灵敏度β的关系以及添加剂对元件的响应与恢复时间的影响。实验结果表明:WO3基元件掺入质量分数为0.5%的PdC l2在加热功率为600mW下可制作成反应能力强、灵敏度高的乙醇气敏元件。     

Influence of humidity on CO sensing with p-type CuO thick film gas sensors

A model for the detection of CO in the presence of humidity is proposed for thick porous film gas sensors based on p-type CuO. The sensing mechanism is investigated by means of simultaneous DC electrical resistance and work function changes measurements combined with appropriate modeling of the conduction in the polycrystalline sensing film. The experiments were performed at 150 °C in dry and humid air backgrounds. The conclusion is that, very similarly to the case of undoped SnO₂, the explanation of the cross-interference of water in the CO detection is the fact that both react with pre-adsorbed oxygen ions.     

Ion sensitive field effect transistor with amorphous tungsten trioxide gate for pH sensing

In this study, the pH sensitive properties of the amorphous tungsten trioxide (a-WO₃) thin films by rf sputtering system from a-WO₃ target have been investigated. The a-WO₃ thin films with 600–4750 Å thickness were deposited on the electrolyte–insulator–semiconductor (EIS) structure maintained at room temperature and a total pressure of 30 mTorr in Ar mixed O₂ gas for 0.5–2 h, and we could obtain the electrical resistivity of the a-WO₃ films, was about 7.8×10⁵–4.5×10⁹ Ω-cm. The EIS structure with a-WO₃ thin films can be used to detect the ion sensitivity and can be explained by C–V curve in the different acidic buffer solutions (pH=1–7) using the C–V measurement. In addition, the a-WO₃ thin films were also deposited on the double layer structure of a-WO₃/SiO₂ gate ion sensitive field effect transistor (ISFET), and these devices were packaged with epoxy. Then, we can obtain the shift of the linear region threshold voltage (ΔV_T) of the ISFET devices in the acidic solutions (pH=1–7). The a-WO₃ materials exhibited a fairly high response, and the sensitivity was about 50 mV/pH.     

Fabrication of a silicon based vertical sensitive low-g inertial micro-switch for linear acceleration sensing

Microsystem Technologies - Most of the MEMS inertial switches developed in recent years are intended for shock and impact sensing with a threshold value above 40 g. These switches were...     

Vic-dioximes: A new class of sensitive materials for chemical gas sensing

Vic-dioximes, a class of organic chemical compounds, are proposed and characterized for the first time as sensitive materials for volatile organic compound sensing with sorption based chemical gas sensors. Their peculiar sensing properties described in this work originate in the oxime functional group which is a powerful H bond donor interacting strongly but reversibly with H bond acceptors. These specific interactions result in a high preferential enrichment of analyte molecules with H bonding acceptor capabilities in the sensitive material. Accordingly, sensitivity and selectivity for these compounds of vic-dioxime based sensors are high. The advantageous sensing properties are demonstrated in this work with quartz crystal microbalance sensors using 11 selected volatile organic compounds and a set of vic-dioximes varied in their substituents. Vic-dioximes with short alkylthiol substituents were found highly sensitive to such H bond acceptors as organic amines, alcohols, and esters with partition coefficients up to 26,000. At the same time they showed low affinity for aromatic compounds and chlorocarbons. Vic-dioximes are considered powerful sensing materials and interesting for practical use in chemical gas sensor arrays.