Semiconductor gas sensors based on metal oxide nanostructures such as WO3 are emerging technologies. The operating principles of these sensors are based on changing the conduction of the sensitive layer in contact with the gases, which are absorbed on their surface. These active sensing materials are deposited on insulating substrates with conductive electrodes, which make their conductivity changes measurable. These sensors can be used to detect hazardous gases such as H2, CO, SO2, NO2, O3, combustible gases, H2S, NH3 and Volitile Organic Compounds. The main problem of these sensors is the lack of selectivity and sensitivity to all oxidizing and reducing gases. Therefore, efforts are being made to develop sensitive materials with high selectivity while maintaining sensitivity. WO3 is one of the candidates for use as a sensitive material in sensors, due to its interesting chemical and physical propertye. In this project, we intend to study the effects of fabrication conditions and consequently morphology as well as the effect of surface modifications on the sensing properties of tungsten oxide nanostructures. For this purpose, the flame vapor deposition (FVD) method using a device developed in this project is used as a simple, low cost and innovative method with the ability to control the surface properties of tungsten oxide nanostructures and the effect of surface modification by was investigated by adding catalysts like Pd. The parameters studied in deposition process were the relative distances between the substrate and the precursor rod to the nozzle of the oxy-hydrogen flame. The results of structural analysis showed the successful formation of WO3 orthorhombic structure on alumina substrate. In addition, the results of the morphological study of the layers indicated the control of thickness and flame vapor production with the relative distance of the precursor rod to the flamel nozzle. Also, by fixing the distance between the rod and the nozzle, the thickness did not change very much, and by changing the distance between the substrates, only the shape and size of the particles that formed the layers, are changed. Gas sensing properties were eva‎luated in temperature range of 100-250 ºC and concentrations of 1-2500 ppm. Obtained results for gas sensing properitis of fabricated gas sensors indicated the high ability of sensors to fast detection of hydrogen gas at concentrations as low as 1 ppm. The sensors had a good response and recovery time of less than 20 s. By comparing the results and selecting the sensor with the optimum operating conditions (sample S1), other sensor properties such as stability and selectivity were investigated. These results indicate the optimal selectivity and very high stability of the sensor as well as the detection of hydrogen gas up to a very low concentration of 75 ppb. Also during the visiting research period, a study was conducted on the combination of Metal-Organic Frameworks (MOF) with SPR sensor platform to identify the chirality of medicine molecules. For this purpose, TAMOF-1 crystals were used to combine with Au sensors in the SPR system. The effect of different locations of particles such as deposition and growth on the sensor surface, as well as placement of particles before the sensor was investigated using microfluidic chips. The results showed that it was inappropriate to place particles on the sensor surface. By combining TAMOF-1 particles into a sensor platform using microfluidic designs, it was observed that the proposed design has the ability to separate two R and S enantiomers of the ibuprofen molecule. In order to optimize the stability of particles in the sensing process, a microfluidic design was developed inspired by the capillary system of blood vessels, which by increasing the stability of particles within microfluidic channels, the reproducibility of the sensor platform was improved in the identification of R and S enantiomers.

مهدي رنجبر

هادي سلامتي

پرويز كاملي، فاطمه داور، نعيمه ناصري طاهري