Biosensors convert a biological response into an electrical signal. Biosensors use a biological system as the responsive material; enzymes, whole cell metabolism, ligand binding and the antibody-antigen reaction, for example. The biological response of the biosensor is determined by the biocatalytic membrane, which converts the substrate to product.
The transducer makes use of the physical change that accompanies the biological reaction. The changes can be one of the following:
the heat output or absorption produced by the biological reaction (calorimetric sensors);
changes in the distribution of charges causing and electrical potential to be produced (potentiometric biosensors);
movement of electrons produced in a redox reaction (amperometric biosensors);
light output or absorption (optical biosensors); or
effects due to the mass of the reactants or products (piezo-electric biosensors).
The output from the transducer is then amplified, processed and displayed.