Electrochemical biosensors• normally based on enzymatic catalysis of a reaction that produces or consumes electrons (such enzymes are rightly called redox enzymes).• The sensor substrate usually contains three electrodes; a reference electrode, a working electrode and a counter electrode.• The target analyte is involved in the reaction that takes place on the active electrode surface, and the reaction may cause either electron transfer across the double layer (producing a current) or can contribute to the double layer potential (producing a voltage
Photometric• Many optical biosensors based on the phenomenon of surface plasmon resonance (SPR) are evanescent wave techniques.• This utilises a property of gold and other materials; specifically that a thin layer of gold on a high refractive index glass surface can absorb laser light, producing electron waves (surface plasmons) on the gold surface.• This occurs only at a specific angle and wavelength of incident light and is highly dependent on the surface of the gold, such that binding of a target analyte to a receptor on the gold surface produces a measurable signal.
Others• Piezoelectric sensors utilise crystals which undergo an elastic deformation when an electrical potential is applied to them. An alternating potential (A.C.) produces a standing wave in the crystal at a characteristic frequency.
Applications• Glucose monitoring in diabetes patients.• Other medical health related targets.• Environmental applications.• Detection of pathogens .• Determining levels of toxic substances before and after bioremediation.• Detection and determining of organophosphate .• Determination of drug residues in food.• Drug discovery and evaluation of biological activity of new compounds.