UBC Theses and Dissertations
Development of highly selective single sensor microfluidic-based gas detector Paknahad, Mohammad
This research aims at the integration of gas sensors into microfluidics platforms to develop low-cost, portable, and highly selective (with a fast recovery time) detection tools for discrimination of volatile organic compounds (VOCs). The main advantage of the proposed device over previous microfluidic-based gas sensors is the enhanced selectivity by optimizing the microchannel geometry and implementing a novel multi-layer surface coating. These enhancements resulted in reducing the sensor recovery time to less than 150 seconds, as opposed to over 15 minutes reported in previous studies. A thorough study is also conducted to further investigate the effect of analyte polarity and the choice of channel surface material (creating different hydrophobicity) on gas discrimination. It is shown that the device segregation capability between different compounds highly depends on the target gas polarity and hydrophobicity of the channel surface material (reflecting its surface energy and interaction with the analyte). Finally, to eliminate the faulty effect of humidity on the sensor’s response, a diffusion-based humidity control membrane (made out of inorganic salts) is added to reduce and stabilize the level of relative humidity at 15%. The transient responses of the sensor in different humidity levels show that the proposed humidity control system also significantly enhances the selectivity of the device. A range of different target analytes including alcohols, ketones, and alkanes are tested using the proposed detector. The results show that the device can successfully differentiate between different gases (and even gas mixtures) at small concentrations (at the ppm level), showing the diagnostic power of the developed sensors. The device is then tested for wide range of applications including: 1) identification of wine samples for which different types of wines from different manufacturers and vintage years are differentiated; 2) monitoring tetrahydrocannabinol (THC) in air samples for potentially detecting the cannabis use; and 3) leakage detection along the pipeline in which the device was used for identifying pentane traces in a field test. This wide range of applications shows the power and versatility of the proposed gas detector technology.
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