Biosensors are devices that combine biological materials and transducers for the detection of sample e.g. drugs, metabolites, pollutants, microbial load, control parameters etc. by converting biochemical signals into measurable physiochemical signals which in turn quantify the amount of sample. There are various types of biosensors depending upon the sensing elements or transducers. Since the first glucose biosensor developed by Clark in 1962 many biosensors have been commercially exploited for various applications as it offers a more specific, sensitive, rapid, real and reproducible results as compared to chemical sensors. Recently nano-biosensors, implanted biosensors and integrated biosensors are in current research and development.

Key words: Biosensors, sensing element, transducer, amperometric, potentiometric, optical.