A biosensor is a analytical device which combines a bio sensing element with a transducer that produces signal

A biosensor is a analytical device which combines a bio sensing element with a transducer that produces signal. This signal result from change in proton concentration, release and uptake of gasses, absorption. The transducer converts the signal into response as current,potential and absorption of light which is amplified, processed and store for future.
Biomolecules as enzymes, antibiotics, receptors and microorganisms are used as biological sensing elements. But microorganisms have more advantage over all these bioelements. They have ability to detect a large number of sensing elements. They have also ability for genetic modification by mutation and Recombinant DNA technology. They can live in harsh conditions and they can also degrade new molecules with time. They can bear a wide range of pH and temperature. Microbes are also useful in fabrication of biosensors.
Microorganisms are inserted with many transducers as amperometric, potentiometric, calorimeteric to construct biosensors devices.
Viable microbes metabolize various organic compounds aerobically and anaerobically and produce their finished products like ammonia, carbon dioxide, acids etc.