According to the definition of a gas sensor, given by the International Union of Pure
and Applied Chemistry (lUPAC), "a chemical sensor is a device that transforms chemical information, ranging from the concentration of a specific sample component to total
composition analysis, into an analytically useful signal. The chemical information,
mentioned above, may originate from a chemical reaction of the analyte or from a physical
property of the system investigated" [1]. Typically, chemical sensors consist of two main
parts, a receptor and a transducer. The receptor transforms chemical information into a
form of energy, which can be measured by the transducer. The transducer converts this
energy into a useful, typically electrical, analytical signal.