Chemical sensors using interactive sorptive materials typically involve a "two-step" response mechanism. While the sorptive material collects and concentrates gas phase molecules, the device on which it has been applied transduces the presence of these sorbed molecules into an analytical signal. Usually, the sorptive material is a thin film and the device is a microfabricated structure, although other configurations exist. The film of a sorptive material is often referred to as the "selective layer