(231g) Developing High Performance Low Cost Ammonia Sensors Based on a Substrate-Directed Solution Crystallization Process

The major barriers in commercializing nano/micro-wire technologies are the high price and complicated manufacture methods. Due to these difficulties, very few nano/micro-wire sensors have reached the market in the last decade. This talk focuses on a patented substrate-mediated crystallization process to deposit conductive tetrathiafulvalene (TTF) and tetracyanoquinodimethane (TCNQ) nano/micro-wires directly on sensor substrates. TTF-TCNQ is often considered the first synthesized organic metal with metallic conductivity. This class of charge-transfer salts has the additional advantage of allowing fine tuning of chemical structure and conductivity by pairing an electron donor with different electron receptors or vice versa. Using electrochemical crystallization, we show that it is possible to deposit TTF or TCNQ nano/micro-wires directly across the photolithographic metal contact lines as the sensing element for impedance-based gas sensing. We are applying the charge-transfer salt assembly for ammonia sensing. Exposure to ammonia can cause irritation and serious burns on the skin and in the mouth, throat, lungs, eyes and even death at high levels. There is a market demand for high performance low cost ammonia sensors for wide area and real time monitoring. Our nanowire sensors are capable of detecting ammonia at sub ppm levels within a few minutes. We have achieved higher selectivity especially against humidity variation by using different nanowire materials as sub-units in a sensor array, collecting large amount of impedance spectral data in different gas mixtures, and applying machine learning algorithms to differentiate ammonia and water vapors. We are working with several companies to commercialize this novel gas sensing technology. This work is supported by the National Science Foundation, US Army Research Office, and MTRAC.