Practical organic electronic noses using semi-permeable polymer membranes

Electronic noses (E-noses) mimic olfactory organs and quantify volatile organic compounds (VOCs), emulating the sense of smell, with applications in real-time monitoring of VOCs in food, healthcare, and law enforcement industries. Organic field-effect transistor (OFET) based sensors can be fabricated in large arrays by economical processes, however, lack the selectivity necessary to differentiate wide varieties of VOCs. Here, we explore the use of permeable polymer membranes with OFET sensors to improve their selectivity. Acylated poly(vinyl alcohol) (PVA) derivatives were synthesized, characterized, and evaluated in OFET vapor sensors as tunable membranes. Sensors with and without acylated PVA membranes were tested with VOC analytes. By monitoring drain current over time, we found that membranes dramatically changed responses to different analytes. We show that VOCs including methanol, ethanol, hexane, toluene, tetrahydrofuran, methyl ethyl ketone, and ethyl acetate can all be detected and differentiated with much greater selectivity than sensors without membranes. In particular, methanol and ethanol, which are difficult to differentiate in vapor sensors, showed significant quantitative differences in the initial slope (0.0403 s⁻¹ vs 0.0192 s⁻¹ respectively; 6 σ) and decay constants (5.5 s vs 15.9 s respectively; 26 σ) of their current vs time responses, allowing methanol and ethanol to be differentiated with 100 % confidence. This approach enables the economical fabrication of large varieties of unique organic vapor sensors by simply changing the membrane layer and results in an outstanding level of selectivity for OFET vapor sensors.