Amperometric transducers detect change in current as a result of electrochemical oxidation or reduction. Typically, the bioreceptor molecule is immobilized on the working electrode (commonly gold, carbon, or platinum). The potential between the working electrode and the reference electrode (usually Ag/AgCl) is fixed at a value and then current is measured with respect to time. The applied potential is the driving force for the electron transfer reaction. The current produced is a direct measure of the rate of electron transfer.  The current reflects the reaction occurring between the bioreceptor molecule and analyte and is limited by the mass transport rate of the analyte to the electrode.