No description available.

No description available.

No description available.

When foodstuffs are subject to microbial infection a range of volatile organic compounds (VOCs) are released which can be indicative of both the type and severity of the infection. The bacterium Erwinia carotovora, the primary cause of soft rot, is a major problem in the bulk storage of potato tubers. A number of classes of VOCs have been identified above E. carotovora infected potato tubers, but no disease specific marker has been identified. A number of studies have concluded that the best marker of E. carotovora infection is a substantial increase in the concentration of VOCs in the headspace above the tubers. Chemical sensors which are sensitive to low levels of the VOCs identified in the headspace above infected tubers have been developed. The aim was to use these sensors as the basis of a system for the early detection of soft rot in stored potato tubers. The sensors developed fall into two main categories: those which required heating to elevated temperatures, and those which were operated at ambient temperatures. The sensors operated at ambient temperatures included composites of tin dioxide and chemically prepared polypyrroles. The composites exhibited a high sensitivity to a range of organic vapours (1-100 vpm) and were more sensitive than either tin dioxide or polypyrrole at room temperature. Composites of chemically prepared polypyrroles with various thermoplastics were fabricated and were found to exhibit a high sensitivity to a range of volatile amines. Further studies incorporated chemically prepared polypyrroles into a printing ink vehicle, and sensors constructed from these films displayed good sensitivity, high stability and high mechanical strength. The sensors operated at elevated temperatures included a range of evaporated tin oxide films doped with Pt, CuO and ZnO, plus a range of thick film sensors based on tin dioxide, zinc oxide and mixtures of the two materials. The thick film sensors exhibited the highest sensitivity to the vapours of interest and also gave superior reproducibility of fabrication when compared to the sensors based on evaporated thin films. A synergistic effect appeared to be in operation where tin dioxide and zinc oxide were mixed, with sensors incorporating composites of the two materials exhibiting higher sensitivities than either tin dioxide or zinc oxide alone. A GC-MS study to elucidate the surface reactions occuring on exposure to the vapour, suggested that the synergistic effect was in part due to differences in the catalytic activities/pathways of the two materials. A prototype device was produced based on two evaporated tin dioxide film sensors and one thick film tin dioxidelzinc oxide (50/50 mlm) sensor. The device was tested to various quantities of sound tubers with an infected tuber added. The prototype device was capable of detecting one infected tuber amongst 100kg of sound tubers in a simulated storage crate.

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The aim of this thesis was to develop laterally resolved measurement systems for analysing Metal Insulator Semiconductor (MIS)-based potentiometric chemical sensors. Therefore, the Light-Addressable Potentiometric Sensors (LAPS) principle was used to provide chemical images. Two main system variants were under investigation. The first was a high-resolution so called LAPS-Microscope suitable for life science applications such as the investigation of pH changes of living cells. The second was developed for the analysis of the gas response of alloys on large scale semiconductor samples (25x25 mm2). Therefore, the system was called a LAPS-Macroscope. The LAPS-Microscope resolution depends on the optical focus and semiconductor properties. To reduce the semiconductor dependent resolution, 18 different types of samples were prepared varying the boron and carbon doping in thin silicon films. To analyse the LAPS resolution, different techniques were developed. A resolution improvement down to 3 μm compared to bulk silicon was achieved. A sputter target configuration was developed to produce ternary alloys on semiconductor samples with a continuous gradient in metal concentration. Different analysis methods such as EDX and AES were used to characterise the thin alloy films. Using the LAPS-Macroscope, the gas sensitivity of more than 106 different alloy compositions at a single sample can be investigated. As a result, metal concentration differences down to 0.03% can be distinguished. Typically, the sensor response of 625 different alloy compositions to changes in the hydrogen concentration was investigated within 16 min. The ternary alloy system PdxNiyCo1-x-y was analysed with the LAPS-Macroscope showing that nickel in the range up to 24 atom% reduces the hydrogen sensitivity. There was no significant influence of cobalt in the concentration range tested. Further, poisoning experiments with H2S showed improved behaviour of palladium alloys with nickel in the range of ~5-10 atom%. It was shown that an effective high-throughput method for the characterisation of ternary alloys was established, which is called a Continuous Gradient High Throughput Screening Macroscope CG-HTSM.

Wireless sensor nodes are emerging in a wide range of critical applications such as environmental monitoring, health applications, home automation and military surveillance and reconnaissance. The addition of low power wireless capability to such sensor nodes allows communication between a node and a base station or between nodes, resulting in the formation of wireless sensor networks. Sensor networks can use the information available from the distributed sensor nodes to determine the location and nature of a stimulus or environmental condition. The information collected by the base station can be used to determine the appropriate course of action for dealing with the stimulus. In chemical/biological defense or safety monitoring scenarios, wireless sensor networks can be used to identify and track harmful chemical or biological agents which might be present in a particular area. Due to the potentially remote areas that wireless sensor networks aim to cover, it is essential to minimize the power consumption of a sensor node so that it can operate over a long period of time without a connection to the power grid. Sensor nodes can contain multiple blocks, such as the readout circuit which interfaces with the sensor, an embedded processor, and the wireless transceiver circuits, all of which need to operate on a low power budget. This thesis specifically focuses on design of low power mixed signal readout circuits which interface with chemoresistive chemical sensors, i.e. sensors that demonstrate a variation of resistance (or impedance) in the presence of chemical agents. For this thesis, the sensor can be either a chemoresistive bead or a nanowire. By integrating multiple non-specific chemoresistive sensors together in arrays, a cross-reactive array can be realized, where the combined response of the arrayed sensors can be used to determine analytes present in a mixture even if their concentrations are low. In this thesis, a CMOS resistive readout circuit based on a sigma-delta ADC is presented. The design is used to measure the resistance of chemoresistive beads and nanowires with respect to time. The frequency of the ADC output varies as the resistance of a sensor changes and, based on the magnitude and duration of the variation, the type of chemical agent and its concentration can potentially be estimated. For future cross-reactive sensor applications, an array of 16x16 sites is also included in the readout circuit design. Individual sites in the sensor array can be accessed using addressing blocks which designed to select a particular row and column using an 8-bit addressing system. This thesis also covers the techniques used for integration of chemoresistive beads and nanowires into the array locations provided on the prefabricated CMOS IC. Measurement results that demonstrate the operation of the resistive readout circuitry are presented. Finally, a second readout circuit is proposed to measure complex impedance variations of a sensor device. Measurement of magnitude and phase changes of a sensor device can provide another degree of freedom in the analysis of chemical mixture. Simulation results demonstrating the functionality of the proposed impedance measurement system are also presented. / Master of Science

abstract: Connected health is an emerging field of science and medicine that enables the collection and integration of personal biometrics and environment, contributing to more precise and accurate assessment of the person’s state. It has been proven to help to establish wellbeing as well as prevent, diagnose, and determine the prognosis of chronic diseases. The development of sensing devices for connected health is challenging because devices used in the field of medicine need to meet not only selectivity and sensitivity of detection, but also robustness and performance under hash usage conditions, typically by non-experts in analysis. In this work, the properties and fabrication process of sensors built for sensing devices capable of detection of a biomarker as well as pollutant levels in the environment are discussed. These sensing devices have been developed and perfected with the aim of overcoming the aforementioned challenges and contributing to the evolving connected health field. In the first part of this work, a wireless, solid-state, portable, and continuous ammonia (NH3) gas sensing device is introduced. This device determines the concentration of NH3 contained in a biological sample within five seconds and can wirelessly transmit data to other Bluetooth enabled devices. In this second part of the work, the use of a thermal-based flow meter to assess exhalation rate is evaluated. For this purpose, a mobile device named here mobile indirect calorimeter (MIC) was designed and used to measure resting metabolic rate (RMR) from subjects, which relies on the measure of O2 consumption rate (VO2) and CO2 generation rate (VCO2), and compared to a practical reference method in hospital. In the third part of the work, the sensing selectivity, stability and sensitivity of an aged molecularly imprinted polymer (MIP) selective to the adsorption of hydrocarbons were studied. The optimized material was integrated in tuning fork sensors to detect environmental hydrocarbons, and demonstrated the needed stability for field testing. Finally, the hydrocarbon sensing device was used in conjunction with a MIC to explore potential connections between hydrocarbon exposure level and resting metabolic rate of individuals. Both the hydrocarbon sensing device and the metabolic rate device were under field testing. The correlation between the hydrocarbons and the resting metabolic rate were investigated. / Dissertation/Thesis / Doctoral Dissertation Chemical Engineering 2018

Face à  la menace croissante du terrorisme, il est essentiel de mettre en place des mesures de précaution et des moyens de surveillance permettant d'assurer la sécurité dans les lieux publics. Dans ce cadre, le CEA Le Ripault développe des systèmes de détection portatifs et autonomes dédiés à la détection d'explosifs en phase gazeuse. Cette thèse s'inscrit dans ce projet. L'objectif de cette étude est de concevoir et d'étudier les propriétés de matériaux sensibles fluorescents dédiés à la détection de composés nitroaromatiques tel que le TNT. Ainsi, les propriétés de mise en forme et de détection de différents matériaux, sensibles aux composés nitroaromatiques, ont été étudiées. Après identification du matériau le plus efficace pour cette application, nous avons étudié sa stabilité et nous avons cherché à comprendre le mécanisme de détection associé à ce matériau fluorescent. Les performances du détecteur de composés nitroaromatiques, intégrant ce matériau, ont ensuite été évaluées. / In order to overcome the growing threat of terrorism, it is essential to put into operation preventive measures and means of monitoring to ensure security in public areas. In this context, the CEA Le Ripault develops portable and self-contained detection systems dedicated to the detection of explosives in the gas phase. This PhD work is part of this project. The objective of this study is to design and to assess the properties of fluorescent sensitive materials dedicated to the detection of nitroaromatic compounds such as TNT. Consequently, the ease of deposition, thin films properties and detection performances of several sensitive materials have been considered. After identification of the most effective material for this application, we studied its stability and we searched to understand the detection mechanism associated with this fluorescent material. Then, the performances of the device which incorporate this sensitive material have been evaluated for the detection of nitroaromatic compounds.