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Recent results with solid-state semiconductor gas sensors based on organic sensor elements are reviewed. Devices based on metal phthalocyanines show useful responses to NO2. Lead phthalocyanine combines the highest conductivity with the maximum sensitivity to NO2. A thin-film lead phthalocyanine sensor has successfully been used to monitor NOx produced by shot-firing in coal mines. To obtain reasonable conductance and speed of response and recovery, phthalocyanine sensors have been operated at 170°C. Conducting polymer materials, and particularly chemically doped polypyrrole, show responses to toxic gases at ambient temperature. Initial work, using polypyrrole black impregnated filter paper, showed a response to ammonia. More recently, using polypyrrole films electrochemically deposited over electrode arrays, responses to nitrogen dioxide and hydrogen sulphide have also been obtained. Organic-semiconductor gas sensors may have advantages compared to metal-oxide devices in their sensitivity to toxic gases and in their ability to operate at or near room temperature. However, the mechanisms of device function are not yet well understood.
Miasik et al. (Wed,) studied this question.