Selective modified SnO2-based materials for gas sensors arrays

An enhancement of selectivity of semiconductor gas sensors, based on nanocrystalline SnO2 is reported. It is shown that modification of the surface of crystallites, forming thick films of conductive sensor materials, with catalytic clusters of gold or oxides of ruthenium, nickel, copper and iron allows selective response of sensors to different gases, such as carbon monoxide, ammonia, hydrogen sulfide, nitrogen dioxide and acetone vapor. These selective sensor responses can be obtained in the ranges of gas concentrations close to or below threshold limit values while the working temperature of sensors can be kept below 300 °C. The described approach for modification of selectivity of sensor materials could be used as perspective route in developingselective gas sensors. These results allow us to propose application of obtained materials in electronic nose sensor systems.     

Differential receptors create patterns diagnostic for ATP and GTP

Herein we report the combination of a library of resin-bound sensors along with a multicomponent sensor array. This novel combinatorial array sensor system shows selectivity for nucleotide phosphates in solution. The design of the anchored receptor includes a 1,3,5-trisubstituted-2,4,6-triethylbenzene scaffold coupled with peptide libraries. Each chemosensor is placed into a micromachined cavity within a silicon wafer, and the optical changes observed by a charged-coupled device result in near-real-time digital analysis of solutions. A colorimetric displacement assay was performed, and time-dependent imaging studies of the selected sensing ensembles result in a differential responses upon addition of adenosine 5'-triphosphate (ATP), adenosine 5'-monophosphate (AMP), or guanosine 5'-triphosphate (GTP). An advantage to this approach is that it creates an array of sensors that gives a fingerprint response for each analyte. Principal component analysis indicates that the library of chemosensors can differentiate between ATP, GTP, and AMP. On the basis of factor loading values, individual sensors from the library were sequenced to elucidate their chemical composition.     

Oxygen indicators and intelligent inks for packaging food

The detection of oxygen using optical sensors is of increasing interest, especially in modified atmosphere food packaging (MAP), in which the package, usually containing food, is flushed with a gas, such as carbon dioxide or nitrogen. This tutorial review examines the ideal properties of an oxygen optical sensor for MAP and compares them with those developed to date, including the most recent advances. The basic technologies underpinning the different indicator types are described, examples given and their potential for application in MAP assessed. This tutorial review should be of interest to the MAP industry and researchers in optical sensors and oxygen sensing.     

Resonant multisensor system for high-throughput determinations of solvent/polymer interactions

Solvent-resistant polymers are important in numerous research, engineering, and consumer applications. To address the limitations of existing methods of evaluation of polymer solubility and solvent resistance, we developed and built a 6 x 4 array of resonant acoustic-wave sensors operating in the thickness shear mode (TSM). The application of this system makes possible analysis of nanogram quantities of polymers in small amounts of solvent and permits the simultaneous analysis of multiple samples, such as those produced in combinatorial polymerization reactions. These parallel determinations of polymer/solvent interactions eliminate errors associated with serial determinations. During the periodic exposure of the TSM crystals to polymer/solvent combinations, the mass increase of the crystal is determined, which is proportional to the amount of polymer dissolved and deposited onto the sensor from a polymer solution. We demonstrate our sensor system for reliable quantification of solubility of several types of polymers in various solvents. The high mass sensitivity of our resonant TSM sensors (10 ng), use of only a minute volume of a solvent (< 2 mL), and parallel operation (matching a layout of available 24 well plates) make this system a good fit with available polymer combinatorial synthesis equipment.     

Methodology for the selection of suitable sensors for incorporation into a gas sensor array

An investigation into suitable mathematical techniques which can be used to select sensor components for a gas sensor array is reported. Data from a tin dioxide Taguchi semiconductor sensor array were obtained individually for various organic solvents and analysed using multivariate techniques, including principal component analysis, cluster analysis and star symbol plots. It was shown that the array data produced a series of characteristic response patterns for the analytes. It was also found that analytes of similar chemical nature had similar response patterns, indicating a correlation between sensor interaction and the chemical functional groups of the analyte. The multivariate techniques used proved to be very useful in enabling a suitable selection of the components of the array to be made by identifying which of the components or sensors were acting independently.     

Phosphorescent Sensor Approach for Non-Destructive Measurement of Oxygen in Packaged Foods: Optimisation of Disposable Oxygen Sensors and their Characterization Over a Wide Temperature Range

ABSTRACT

Phosphorescent oxygen sensors were evaluated for their suitability as a non-destructive method of measuring oxygen in packaged foods. Using phosphorescent phase measurements, characteristics of several types of disposable oxygen sensors were studied in order to optimize sensor chemistry, fabrication technology and performance. The optimal sensor was characterized in both the gas phase and in the liquid phase, over a temperature range of –17°C ? +30°C and oxygen concentrations between 0 and 21 kPa. Calibrations, analytical equations and temperature coefficients were obtained, which enabled accurate quantitation of oxygen and correction of optical measurements for sample temperature variations. For disposable sensor elements the resolution of the system at 22°C was about ±0.02 kPa and ±0.5 kPa at 0 and 21 kPa oxygen respectively, and in continuous monitoring mode - ±0.0054 kPa and ±0.081 kPa oxygen, respectively. Results of the use of the oxygen sensors in food packaging applications and practical recommendations are presented.     

Elucidating the Mechanism of Working SnO2 Gas Sensors Using Combined Operando UV/Vis,Raman, and IR Spectroscopy

SnO₂ is the most widely used metal oxide gas‐sensing material but a detailed understanding of its functioning is still lacking despite its relevance for applications. To gain new mechanistic insight into SnO₂ gas sensors under working conditions, we have developed an operando approach based on combined UV/Vis, Raman, and FTIR spectroscopy, allowing us for the first time to relate the sensor response to the concentration of oxygen vacancies in the metal oxide, the nature of the adsorbates, and the gas‐phase composition. We demonstrate with the example of ethanol gas sensing that the sensor resistance is directly correlated with the number of surface oxygen vacancies and the presence of surface species, in particular, acetate and hydroxy groups. Our operando results enable an assessment of mechanistic models proposed in the literature to explain gas sensor operation. Owing to their fundamental nature, our findings are of direct relevance also for other metal oxide gas sensors.     

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 .     

Optimization of Ormosil Films for Optical Sensor Applications

Recent work has indicated that Ormosil films, fabricated from organically modified precursors, produce better sensor performance for some specific applications, compared to films fabricated from conventional sol-gel precursors such as TEOS or TMOS. This paper aims to compare film properties and sensor behavior for films fabricated from tetraethoxysilane (TEOS) and tetramethoxysilane (TMOS) silica precursors and both methyltrimethoxysilane (MTMS) and methyltriethoxysilane (MTES) organically modified precursors. Microstructural differences, for example, porosity changes due to the different precursor backbone structures, are interrogated by monitoring oxygen gas and aqueous-phase sensor response. Oxygen sensing using these films is enabled by incorporating in the films an oxygen-sensitive ruthenium dye whose fluorescence is quenched in the presence of oxygen. Film properties such as thickness, thickness stabilization time, as well as sensor response, are discussed in terms of relative hydrolysis and condensation behavior for the different precursors. Film hydrophobicity, an issue which has been identified as being of crucial importance for optimum dissolved oxygen sensor response, is discussed and contact angle measurements are used to investigate the degree of hydrophobicity for different film types. The main motivation for this work is film optimization for optical gas-phase and dissolved oxygen sensors.     

Characterization of Optical Fiber Dissolved Oxygen Sensor for Aquaculture Sensing and Monitoring

Optical fiber sensor using sol gel membrane incorporated RTV silicon rubber was fabricated and developed for the characterization of dissolved oxygen in aqueous solution. The sol gel materials used consists of Tetraethylorthosilicate (TEOS) and Triethoxyoctylsilane (Octyl-triEOS) as the precursor compound for the preparation of the sol gel structures, while tris-BP Ruthenium (II) chloride as the fluorescent lifetime of the oxygen indicator. Dip coating techniques is utilized to position the sol gel technology at the distal end of the optical fiber. Dissolved oxygen gas sensor characterizations include a study on the sensitivity, temperature effects and drift rate of the sensor performance when measured in 40ppt salt water. Potential applications of the optical fiber sensor are including aquaculture, river monitoring and environment sector.     

基于石墨烯光子晶体光纤的流体传感器

与传统的传感器设备阵列相比,由于结构更为简单,具有广泛检测兼容性的光纤系统逐渐成为分布式监测的有力候选者。然而,受工作机制的限制,大多数光纤传感器仍局限于对折射率等物理参数进行探测,一种用于环境化学监测的全光纤分布式传感系统亟待研发。本工作中,我们向化学气相沉积法生长的石墨烯光子晶体光纤(Gr-PCF)中引入了一种化学传感机制。初步结果表明,石墨烯光子晶体光纤可以选择性地检测浓度为ppb级的二氧化氮气体,并在液体中表现出离子敏感性。石墨烯光子晶体光纤与光纤通信系统的波分、时分复用技术结合后,将为实现分布式光学传感环境问题提供巨大的潜力和机会。     

Recent developments on application of nanometal-oxide based gas sensor arrays

It is shown that the sensor arrays can acquire more information on a given sample than an individual sensor. The main classes of gas-sensing materials include metal-oxide semiconductors. Gas sensors based on chemiresistive semiconducting metal-oxides have many potential benefits including, their very low cost, fast response, recovery time, simple electronic interface, ease of use, and ability to detect a large analytes. Recent advances in gas sensor arrays have shown the capability to incorporate nanomaterial based cross-reactive array. In this way it is possible to increase the surface/volume ratio of the sensing layer. Therefore the surface scattering is better influenced by adsorbed species and change in sensor conductivity is higher. Also the sensitivity of semiconductor oxide materials can be improved by using of nanoparticles. Gas sensor arrays based on nanotechnology can rapidly, sensitively, and selectively detect target molecules.     

In vivo monitoring of the gastrooesophageal system using optical fibre sensors

In the present paper optical fibre sensors for the detection of foregut diseases are described, in particular, sensors for the detection of bile, carbon dioxide and pH. Bile-containing refluxes are measured by means of a sensor which uses bilirubin as natural marker. The sensor, which is already present on the market, has been clinically validated by various hospitals. The clinically relevant parameter is the exposure time of the stomach/oesophagus mucosa to the bile. When measured in the oesophagus, it has been shown to be closely correlated with the onset of Barrett's oesophagus or general oesophagitis. Recently, optical fibres have been proposed for the continuous monitoring of carbon dioxide in the stomach: an important parameter in critically ill patients. A clinically validated prototype has shown its superiority in comparison with the traditional method, that is based on gastric tonometry. For the sake of completeness, also gastric pH sensors are considered, although at the moment their development is stationary at the laboratory stage.     

Efficient split synthesis for targeted libraries

We propose a new approach for fabricating more sophisticated combinatorial chemistry libraries via split synthesis and evaluate its potential through extensive simulation. Our algorithmically intensive method promises to reduce the time and materials costs of synthesizing libraries which are (1) too large to synthesize economically by sequential or parallel synthesis, (2) too long or irregular for conventional split synthesis generation techniques, and (3) not used in sufficient quantity to justify the setup costs of array makers. It also encourages the design of more focused and interesting libraries than are typically constructed using split synthesis. Our algorithms automate the design of efficient synthesis procedures for motif-based libraries which are too complex to design by hand. Our software allows the user to select the most desirable tradeoff between minimizing the number of steps in the synthesis process and containing the combinatorial explosion of the number of compounds synthesized.     

Sol–gel immobilized room-temperature phosphorescent metal-chelate as luminescent oxygen sensing material

The chelate formed by 8-hydroxy-7-iodo-5-quinolinesulfonic acid (ferron) with aluminium exhibits strong room-temperature phosphorescence (RTP) when retained on a solid support. In a previous paper we have found that sol–gel technology is a very useful approach for developing RTP optical sensors as a new way to immobilize lumiphors. Sol–gel active phases proved to exhibit a high physical rigidity that enhanced relative RTP intensities and triplet lifetimes of the immobilized probe. In this paper we present an optical sensing phase prepared using the Al–ferron chelate which displays RTP entrapped in a sol–gel glass matrix for the determination of very low levels of oxygen both dissolved in water and organic solvents and in gaseous media. The sol–gel sensing material has proved to be chemically stable for at least 6 months under ambient storage conditions. Besides a high reproducibility in the formation of the sensing materials and no leaching or bleaching of the trapped reagent (neither in the gas phase nor in water or organic solvents) was observed. Oxygen was determined by continuous flow and flow injection methods using both intensity and triplet lifetime measurements. Both methods provided a fast response, good reproducibility and detection limits of 0.0005% (v/v) in the gas phase and <0.01 mg l⁻¹ for dissolved oxygen. An exhaustive study of the effect of some possible interferents present in the gas phase or in solution demonstrated the high specificity of this phosphorescent probe. This highly sensitive oxygen probe has been successfully applied to dissolved oxygen determinations in river and tap waters and its coupling to fiber optics for RTP in-situ monitoring or remote sensing of oxygen has been evaluated.     

基于半导体纳米SnO_2构建的气敏传感器的应用研究进展

SnO2是传统的气敏材料,由于其具有间隙锡离子和氧空位的特性,使得气体更容易吸附在材料表面,从而显示出更好的气敏性质.通过把SnO2进行贵金属附载掺杂和多种气敏性半导体氧化物的复合,探讨了一系列性能良好的气敏传感器,阐述了SnO2气敏传感的最新进展.     

Intrinsic Artefacts in Optical Oxygen Sensors—How Reliable are our Measurements?

Optical oxygen sensing is of broad interest in many areas of research, such as medicine, food processing, and micro‐ and marine biology. The operation principle of optical oxygen sensors is well established and these sensors are routinely employed in lab and field experiments. Ultratrace oxygen sensors, which enable measurements in the sub‐nanomolar region (dissolved oxygen), are becoming increasingly important. Such sensors prominently exhibit phenomena that complicate calibration and measurements. However, these phenomena are not constrained to ultratrace sensors; rather, these effects are inherent to the way optical oxygen sensors work and may influence any optical oxygen measurement when certain conditions are met. This scenario is especially true for applications that deal with high‐excitation light intensities, such as microscopy and microfluidic applications. Herein, we present various effects that we could observe in our studies with ultratrace oxygen sensors and discuss the reasons for their appearance, the mechanism by which they influence measurements, and how to best reduce their impact. The phenomena discussed are oxygen photoconsumption in the sensor material; depletion of the dye ground state by high‐excitation photon‐flux values, which can compromise both intensity and ratiometric‐based measurements; triplet–triplet annihilation; and singlet‐oxygen accumulation, which affects measurements at very low oxygen concentrations.     

共轭聚合物在传感器上的应用

由于其特殊的光学和电子性质,共轭聚合物受到人们的广泛关注.共轭聚合物可以在各种传感器件中用作活性材料,例如:生物传感器;气体、湿度传感器;离子传感器;压力、温度传感器等.本文综述了共轭聚合物在传感器应用方面的一些新的进展.     

Recent advances in liquid-phase combinatorial chemistry

In combination with high throughput screening, combinatorial organic synthesis of large numbers of pharmaceutically interesting compounds may revolutionize the drug discovery process. Although combinatorial organic synthesis on solid supports is a useful approach, several groups are focusing their research efforts on liquid-phase combinatorial synthesis by the use of soluble polymer supports to generate libraries. This macromolecular carrier, in contrast to an insoluble matrix, is soluble in most organic solvents and has a strong tendency for precipitation in particular solvents. Liquid-phase combinatorial synthesis is a unique approach since homogeneous reaction conditions can be applied, but product purification similar to the solid-phase method can be carried out by simple filtration and washing. This method combines the positive aspects of classical solution-phase chemistry and solid-phase synthesis. This review examines the recent applications (1995-1999) of soluble polymer supports in the synthesis of combinatorial libraries.