Gas sensor array based on metal-decorated carbon nanotubes

Here we demonstrate design, fabrication, and testing of electronic sensor array based on single-walled carbon nanotubes (SWNTs). Multiple sensor elements consisting of isolated networks of SWNTs were integrated into Si chips by chemical vapor deposition (CVD) and photolithography processes. For chemical selectivity, SWNTs were decorated with metal nanoparticles. The differences in catalytic activity of 18 catalytic metals for detection of H(2), CH(4), CO, and H(2)S gases were observed. Furthermore, a sensor array was fabricated by site-selective electroplating of Pd, Pt, Rh, and Au metals on isolated SWNT networks located on a single chip. The resulting electronic sensor array, which was comprised of several functional SWNT network sensors, was exposed to a randomized series of toxic/combustible gases. Electronic responses of all sensor elements were recorded and the sensor array data was analyzed using pattern-recognition analysis tools. Applications of these small-size, low-power, electronic sensor arrays are in the detection and identification of toxic/combustible gases for personal safety and air pollution monitoring.     

An independently addressable microbiosensor array: what are the limits of sensing element density?

A microdisc sensor array, prepared by thin film technology, has been used as a model for miniaturized multi-functional biosensors. It consists of a series of wells, 20 microns in diameter, possessing a 1000 A Pt layer at the bottom that serves as the indicating electrode. The depth of the wells ranged from 2.3-24 microns, depending on the photoresist employed and the spinning speed used to coat the electrode interconnect grid. Ten such wells were arranged in a circular array within an area of radius 130 microns. The center to center distance between any two of the discs ranged from 30 to 155 microns. Each disc is connected by a conductive film line to corresponding pads on the side of the sensor chip. A cylinder placed on top of the chip array formed the electrochemical cell into which a common reference and counter electrode were placed. The reference electrode was operated at ground potential. Prior to the evaluation of enzyme sensors, an assessment of "chemical cross-talk", the perturbation of sensor response resulting from the overlap of proximal diffusion layers, was made using Fe(CN)6(4-). The preliminary conclusion is that the sensing elements probably must be separated by about 100 microns in order to avoid interference from adjacent sensors. A technique was developed for the precision delivery of enzyme and cross-linking agent to the 2.3 microns cavity, having a capacity of 4 pL. This procedure makes possible the preparation of sensor arrays capable of detecting different analytes by employing different enzymes. The sensors gave reasonably rapid (2-4 s) response with linearity (up to about 10 mM. However, the sensors in the center of the array clearly showed the effects of depletion of substrates by the surrounding sensors.     

Rapid, sensitive, and multiplexed on-chip optical sensors for micro-gas chromatography

We developed and characterized a rapid, sensitive and integrated optical vapor sensor array for micro-gas chromatography (μGC) applications. The sensor is based on the Fabry-Pérot (FP) interferometer formed by a micrometre-thin vapor-sensitive polymer layer coated on a silicon wafer. The thickness and the refractive index of the polymer vary in response to the vapor analyte, resulting in a change in the reflected intensity of the laser impinged on the sensor. In our study, four different polymers were coated on four wells pre-etched on a silicon wafer to form a spatially separated sensor array. A CMOS imager was employed to simultaneously monitor the polymers' response, thus enabling multiplexed detection of a vapor analyte passing through the GC column. A sub-second detection time was demonstrated. In addition, a sub-picogram detection limit was achieved, representing orders of magnitude improvement over the on-chip vapor sensors previously reported.     

Chemically Induced Sintering of Nanoparticles

We have observed solid‐state growth of pre‐existing silver nanoparticles (AgNPs) upon exposure to trace (ppb) concentrations of reactive gases at room temperature. The consequent change in localized surface plasmon resonances alters the visible absorbance of dried, printed sensor spots made from inks of 10 nm‐AgNPs and provides a novel mechanism for trace detection and dosimetry of reactive gases. Colorimetric sensor arrays based on these AgNP inks offer dosimetric identification of acidic and oxidizing gases and other reactive vapors with limits of detection below ppb levels for 1 h exposures. For an array of AgNP inks with various capping agents, a unique color response pattern is observed for each specific analyte. Excellent discrimination among 11 reactive gases was demonstrated using standard chemometric methods. The chemically induced sintering of NPs paves the way for novel solid‐state sensors for the ultrasensitive detection of reactive gases and their application to the monitoring of trace airborne pollutants.     

基于纳米银的比色阵列传感器的构建及在蛋白质检测中的应用

蛋白质的快速高效检测和鉴定在医学诊断、不同疾病的治疗和蛋白质组学中具有巨大的前景。目前的检测手段大多存在一些问题,如操作繁琐、效率低等,因此开发一个理想的蛋白质检测方法尤为重要。以纳米银(AgNPs)为传感元件的阵列传感器在蛋白质检测方面具有操作便捷、准确率高、可视化等优点。本文合成两种不同颜色和形状的AgNPs:黄色球形和蓝色三角形,以此构建一个简单的比色阵列传感器,用于蛋白质的区分检测。该传感器可以准确地识别和区分不同种类的蛋白质,准确率为100%。在成功识别出不同类型的蛋白质的基础上,进一步评估了该阵列传感器应用于区分正常和变性蛋白质的能力,准确率为96.0%。此外,该阵列传感器对于未知样本的识别也具有高的准确率。     

Rare earth ions-enhanced gold nanoclusters as fluorescent sensor array for the detection and discrimination of phosphate anions

The discrimination and detection of phosphate anions have attracted extensive attention due to their important roles in various biological processes. Compared with sensors to detect one individual phosphate at a time, sensor arrays are able to discriminate multiple phosphates simultaneously. In this study, we developed a rare earth ions enhanced AuNCs-based sensor array to achieve facile and rapid identification of phosphate anions (PPi, ADP and ATP). The rare earth ions (i. e., Ce³⁺, Gd³⁺, Tm³⁺ and Yb³⁺) can significantly enhance the fluorescence of AuNCs through aggregation-induced emission effect. And the subsequent addition of phosphate anions can recover the fluorescence of the AuNCs-rare earth ions assembly. Thanks to the different numbers of phosphate group and different steric hindrance effects of phosphate anions, the recovery fluorescence of AuNCs-rare earth ions assembly induced by PPi, ADP or ATP are respectively distinct. Thus the sensor array composed of AuNCs and different rare earth ions is able to distinguish those phosphate anions. Finally, the sensor array was successfully demonstrated to identify the phosphates in blind samples.     

脉冲电势调制型电化学气体传感器

根据暂态电化学原理 ,使用微电极并融合计算机控制的快速电势调制技术和数据采集、处理功能 ,提出并建立了一类全新的集信号提取、处理与结果显示等功能于一体的“脉冲电势调制型气体传感器” .在优化传感器性能及其新的功能开发和集成方面取得了重要进展 ,是一类为常规电化学气体传感器无法比拟而有发展前景的暂态电化学多组份气体传感器 .     

Application of a Chemical Sensor Array to Assessing the Presence of Neoplasms by Blood Smell

The results of using a piezosensor array for assessing the presence of benign and malignant neoplasms in gynecologic patients by the presence and concentration of marker gases in the headspace of blood samples are discussed. With the help of identification parameters of the sensor array, marker gases of the investigated pathological processes were detected in the headspace of blood samples, and the features of their composition depending on the type of tumor were determined. A model was developed using partial least squares regression to obtain fast screening information (sick/healthy) from the results of adsorption of headspace of blood samples. The correctness, sensitivity, and specificity of the proposed approach to the detection of marker gases in the headspace of blood samples using an array of chemical sensors are estimated.     

Electronic Noses Using Quantitative Artificial Neural Network

The present paper covers a new type of electronic nose (e-nose) with a four-sensor array, which has been applied to detecting gases quantitatively in the presence of interference. This e-nose has adapted fundamental aspects of relative error (RE) in changing quantitative analysis into the artificial neural network (ANN). Thus, both the quantitative and the qualitative requirements for ANN in implementing e-nose can be satisfied. In addition, the e-nose uses only 4 sensors in the sensor array, and can be designed for different usages simply by changing one or two sensor(s). Various gases were tested by this kind of e-nose, including alcohol vapor, CO, iiquefied-petrol-gas and CO2. Satisfactory quantitative results were obtained and no qualitative mistake in prediction was observed for the samples being mixed with interference gases.     

Electronic Noses Using Quantitative Artificial Neural Networ

The present paper covers a new type of electronic nose(e-nose) with a four-sensor array,which has been applied to detecting gases quantitatively in the presence of interference. This e-nose has adapted fundamental aspects of relative error(RE) in changing quantitative analysis into the artificial neural network (ANN).. Thus, both the quantitative and the qualitative requirements for ANN in implementing e-nose can be satisfied. In addition, the e-nose uses only 4 sensors in the sensor array, and can be designed for different usages simply by changing one or two sensor(s). Various gases were tested by this kind of e-nose, including alcohol vapor, CO, liquefied-petrol-gas and CO2. Satisfactory quantitative results were obtained and no qualitative mistake in prediction was observed for the samples being mixed with interference gases.     

Low temperature H2S sensor based on copper oxide/tin dioxide thick film

Nanostructured tin dioxide (SnO2) powders were prepared by a sol-gel dialytic process and and the doping of CuO on it was completed by a deposition-precipitation method. The thick film sensors were fabricated from the CuO/SnO2 polycrystalline powders. Sensing behavior of the sensor was investigated with various gases including CO, H2, NH3, hexane, acetone, ethanol, methanol and H2S in air. The as-synthesized gas sensor had much better response to H2S than to other gases. At the same time, the CuO/SnO2 sensor had enough sensitivity, together with fast response and recovery, to distinguish H2S from those gases at 160 and 210 ℃. Therefore, it might have promising applications in the future.     

氧化镍-铁酸锌复合薄膜/锡掺杂玻璃光波导传感元件的制备及其对硫化氢气体的气敏性

用溶胶-凝胶法制成了NiO掺杂的ZnFe2O4溶胶,并用浸渍提拉法将其固定在锡掺杂玻璃光波导表面,研制了NiO-ZnFe2O4复合薄膜/锡掺杂玻璃光波导气敏元件,并对无机有毒气体进行了检测。 实验结果表明,在室温下,该传感元件对H2S气体具有一定的选择性响应,而对相同浓度的其它无机气体的响应相对较小,能够检测到1.0×10-9（体积比）的H2S气体,其响应和恢复时间分别是6和8 s。 该元件具有灵敏度高、响应-恢复快、可逆性和重复性好、容易制备,在室温下便于操作等特点。     

Solid-state potentiometric gas sensors—current status and future trends

The development of potentiometric sensors for monitoring environmental gases has become a well-established direction in sensor technology. Various types of potentiometric sensors employing solid electrolytes for in situ measurements of such gases as oxygen, hydrogen, carbon dioxide, sulfur oxides, carbon monoxide, nitrogen oxides, and hydrocarbons are reviewed. Particular concern was given to the CO₂ potentiometric sensor which is an example of successful commercial application. The construction details, working mechanism, and performance of different types of potentiometric gas sensors are given. Special emphasis is given for the mixed-potential electrodes, which seems to be the principal direction for the future research and development of the sensor science and technology. Additionally, the future use of potentiometric sensors for the detection of other environmental gases is discussed.     

Low temperature H_2S sensor based on copper oxide/tin dioxide thick film

Nanostructured tin dioxide (SnO2) powders were prepared by a sol-gel dialytic process and and the doping of CuO on it was completed by a deposition-precipitation method.The thick film sensors were fabricated from the CuO/SnO2 polycrystalline powders.Sensing behavior of the sensor was investigated with various gases including CO,H2,NH3,hexane,acetone,ethanol,methanol and H2S in air.The as-synthesized gas sensor had much better response to H2S than to other gases.At the same time,the CuO/SnO2 sensor had enough sensitivity,together with fast response and recovery,to distinguish H2S from those gases at 160 and 210 ?C.Therefore,it might have promising applications in the future.     

Al掺杂α-Fe2O3材料的制备、表征和气敏特性

采用均相沉淀法制备了纯α-Fe2O3(300 ℃煅烧)和Al掺杂α-Fe2O3(300和400 ℃煅烧), 使用SEM, XRD, ICP和红外光谱等手段进行表征, 并利用气敏仪测试无水乙醇和90＃汽油在不同条件下对材料的响应性能. 结果表明, 微量Al掺杂不改变α-Fe2O3材料的物相, 但会阻碍晶粒生长, 使颗粒变小及Fe2O3晶格间隙中的铁原子数目增多, 材料的导电率增大, 从而显著提高材料的气敏性能. Al掺杂α-Fe2O3对乙醇的响应性能优于对汽油的响应性能, 在乙醇气氛中, 材料对湿度仍然不敏感. 经400 ℃煅烧的Al掺杂α-Fe2O3稳定性较好, 可作为检测乙醇气体的半导体气敏材料.     

Electrochemical sensing of gases based on liquid collection interfaces

Although many electrochemical gas sensors have been reported, electrochemical gas sensors based on liquid collection constitute a smaller subset. Minimally, a liquid interface based electrochemical gas sensor is composed of two electrodes and an ion conducting electrolyte. There is a large number of possible arrangements of these parts, and many choices exist for their composition and preparation methods. This results in a diverse and rich technology now available for gas sensing. The measurement of some analyte gases of interest, notably ozone, nitrogen oxides, hydrogen peroxide, formaldehyde, ammonia, sulfur dioxide and hydrogen sulfide are specifically discussed. Finally, the recent reviews that are likely to be the most relevant to the further development of electrochemical detection approaches for gases with a liquid collection interface are cited and discussed.     

Nano‐Graphene Oxide Based Multichannel Sensor Arrays towards Sensing of Protein Mixtures

Optical array‐based sensors are attractive candidates for the detection of various bio‐analytes due to their convenient fabrication and measurements. For array‐based sensors, multichannel arrays are more advantageous and used frequently in many electronic sensors. But most reported optically array based sensors are constructed on a single channel array. This difficulty is mainly instigated from the overlap in optical responses. In this report we have used nano‐graphene oxide (nGO) and suitable fluorophores as sensor elements to construct a multichannel sensor array for the detection of protein analytes. By using the optimized multichannel array we are able to detect different proteins and mixtures of proteins with 100 % classification accuracy at sub‐nanomolar concentration. This modified method expedites the sensing analysis as well as minimizes the use of both analyte and sensor elements in array‐based protein sensing. We have also used this system for the single channel array‐based sensing to compare the sensitivity and the efficacy of these two systems for other applications. This work demonstrated an intrinsic trade‐off associated with these two methods which may be necessary to balance for array‐based analyte detections.     

Method of gas mixtures discrimination based on sensor array, temporal response and data driven approach

This work presents a method of gas mixtures discrimination. The principal concept of the method is to apply measurement data provided by a combination of sensors at single time point of their temporal response as input of the discrimination models. The pattern data combinations are selected for classes of target gases based on the criterion of 100% efficient discrimination. Combinations of sensors and time points, which provide pattern data combinations in course or repeated measurements, are encoded in the form of addresses. The designer of sensor system is responsible for their selection and they are included in the software of the final instrument. The study of the method involved the discrimination of gas mixtures composed of air and single chemical: hexane, ethanol, acetone, ethyl acetate and toluene. Two sensor arrays were utilized. Each consisted of six TGS sensors of the same type. The dynamic operation of sensors was employed. As an example the stop-flow mode was chosen. The work provides the evidence of the existence of sensor combinations and time points, which are successful in discrimination of studied classes of target gases. The persistence of addresses was discussed considering the ability of sensor array to recognize analytes, variability of repeated measurement results, number of repeated measurements and a twin sets of sensors. Altogether, the validity of the method was demonstrated.     

Hybrid Electronic Tongue as a Tool for the Monitoring of Wine Fermentation and Storage Process

Hybrid electronic tongue based on potentiometric and voltammetric sensors was applied for the monitoring of wine production process. The sensor array formed by miniaturized ion‐selective electrodes and glassy carbon electrodes provided the analysis of the progress and correctness of wine fermentation and storage process, detection of the presence of disturbing factors and evaluation of the quality of final product. The efficiency of the proposed approach was compared with the monitoring of wine production carried out using standard reference methods. The results indicated that hybrid electronic tongue could be used as simple and reliable analytical tool dedicated to qualitative and quantitative assessment of wine production.     

An optical waveguide acid vapor sensor

An optical waveguide sensor for the detection of acid vapors is described. The chemically sensitive reagent coating consists of bromothymol blue indicator suspended in a Nafion polymer film. The sensor uses a 562 nm LED source and a phototransistor detector. Response to hydrochloric acid and hydrogen sulphide vapours is both rapid and reversible, with an estimated detection limit for hydrogen sulphide of less than 15 ppm. The sensors exhibits generalized response to protonic acid vapours, but does not produce an indicator response to carbon dioxide, even at large concentrations (1100 mg/l.) in the presence of water vapor. The sensor exhibits a systematic interference from water vapor which may be corrected by a different approach, either using a reference sensor (Nafion/no indicator) or by monitoring sensor response at two wavelengths.