(496a) Microfabricated Electrochemical Organophosphate Sensor Based on Oxime Chemistry

Recently, interest in the organophosphate (OP) sensor has multiplied, especially after the tragic terrorist attack with sarin in Tokyo in 1995. While the conventional gas chromatography and mass spectroscopy are well-established methods for the detection of OP toxins, there are strong demands for portable OP sensors that have high chemical selectivity in field operation, where various chemicals are mixed with target OP compound and interfere with detection. In this work, we evaluate and optimize an electrochemical sensor based on oxime chemistry, in which keto-oxime reacts with OP toxins and produces cyanide which is detected electrochemically. In order to build an electrochemical gas sensor that responds rapidly (less than 10sec) to a very low level of gas (order of ppb), it is critical to have a high-area gas-electrolyte interface and to minimize the volume of the electrolyte, so that electrolyte solution is contained in one side and target gas molecule dissolves effectively into the electrolyte. We take two approaches to accomplish the goal. (1) Several nanoporous membranes are evaluated and optimized to construct the gas-electrolyte interface. This scheme can be generalized to any electrochemical gas sensors. Also, in order to detect an extremely low lever of gas, we made a thin-layer type electrochemical cell and minimized the electrolyte volume. (2) Microfabricated fluidic channels are utilized. Either segmented gas-liquid flow through a single channel or nanoporous membrane sandwiched between two channels provide a good gas-liquid interface. With microchannels, it is also much easier to regenerate the electrolyte solution simply by replacing the electrolyte solution in the cell.