A device that uses an immobilized agent to detect or measure a chemical compound.

The agents include enzymes, antibiotics, organelles, or whole cells

A reaction between the immobilized agent and the molecule being analysed is transduced into an electronic signal. This signal may be produced in response to the presence of a reaction product, the movement of electrons, or the appearance of some other factor (e.g light)

Biosensors are being used increasingly in diagnostic tests these allow quick, sensitive, and specific analysis of a wide range of biological products, including antibiotics, vitamins and other important biomolecules as well as the determination of certain xenobiotics, such as synthetic organic compounds.