There are strong demands for sensors of toxic chemicals such as organophosphate (OP) and cyanide. One of the approaches for high-selectivity sensor is to utilize a specific chemical or biological interaction of the target molecule. Recently, we showed that the electrochemical sensor based on oxime chemistry has high selectivity, in which keto-oxime reacts with OP toxins and produces cyanide which is detected electrochemically. One of the bottlenecks in detecting an ultra-low level of toxic chemicals is the detection limit of the sensing electrode. We take two approaches to build a highly sensitive and selective sensing electrode. (1) Several silver-based materials are evaluated and optimized, such as silver nanodeposits on graphite or nanoporous silver membrane, which would show better performance than bulk electrode. (2) Enzyme-based sensing scheme is utilized, which would show inherently high chemical selectivity toward the target molecules.