Future research directions remain. The first is to develop a model of the second form of a catalytic filter: a catalytic film overlaying the recognition element. We hypothesize an optimal thickness of the catalytic film exists-especially when response times are considered, as the gas must diffuse through the catalytic film to reach the recognition element of the sensor. The second is to take a Bayesian perspective of inverse problems to impose a Bayesian performance metric on the gas sensor. The third is to carry out experiments to verify the existence of an optimal residence time in the catalytic filter.