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A biosensor is an analytical device for the detection of an analyte that combines a biological component with a physicochemical detector component. Did you know a biosensor has the ability to trace even the chemical constituents in a food? Yes, they really can detect the minute nutrients present in food commodity. A biosensor basically has 3 parts:

The sensitive biological element (e.g. tissue, microorganisms, organelles, cell receptors, enzymes, antibodies, nucleic acids, etc.), a biologically derived material or biometric component that interacts (binds or recognises) with the analyte under study. The biologically sensitive elements can also be created by biological engineering.

The transducer or the detector element (works in a physicochemical way; optical, peizoelctric, electrochemical, etc.) that transforms the signal resulting from the interaction of the analyte with the biological element into another signal (i.e., transducers) that can be more easily measured and quantified;

Associated electronics or signal processors that are primarily responsible for the display of the results in a user friendly way. This sometimes accounts for the most expensive part of the sensor device; however it is possible to generate a user friendly display that includes transducer and sensitive element.

A common example of a commercial biosensor is the blood glucose biosensor, which uses the enzyme glucose oxidase to break blood glucose down. In doing so it first oxidizes glucose and uses two electrons to reduce the FAD (A component of the enzyme) to FADH2. This in turn is oxidized by the electrode (accepting two electrons from the electrode) in a number of steps. The resulting current is a measure of the concentration of glucose. In this case, the electrode is the transducer and the enzyme is the biologically active component.

In the wasp hound odor-detector, the mechanical element is a video camera and the biological element is five parasitic wasps which have been conditioned to swarm in response to the presence of a specific chemical. Current commercial electronic noses, however, do not use biological elements. A canary in a cage, as used by miners to warn of gas, could be considered a biosensor. Many of today's biosensor applications are similar, in that they use organisms which respond to toxic substances at a much lower concentrations than humans can detect to warn of the presence of the toxin. Such devices can be used in environmental monitoring, trace gas detections and in water treatment facilities.