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Biosensors and BiochipsBIO. "Biotechnology in Perspective." Washington, D.C.: Biotechnology Industry Organization, 1990.The high degree of specificity exhibited by the actions of enzymes, antibodies, and membrane receptors offers the potential of developing sensors or detectors that possess unparalleled chemical recognition properties. Biotechnologists are beginning to exploit this vast resource of sensors and, where this exquisite biological sensitivity can be coupled to the unique ability of microelectronic circuits to amplify and process minute electronic signals, biosensors capable of detecting extremely low levels of proteins, hormones, pollutants, gases, and other molecules can be developed.
Diagnosis, Health, and SafetyBiosensors will assist doctors in making rapid diagnoses. They are finding applications in industry, where they permit rapid detection and measurement of acids, alcohols, and phenols. Diagnostic kits for the detection of small amounts of drugs in humans are assisting the police and doctors in assessing drug abuse. Advanced systems are being developed in which biosensors are coupled to alarm systems warning workers of dangers before they reach critical levels. The benefits in health and safety at the workplace will be considerable.
Bugs and ComputersIn a typical biosensor, the substance to be detected or measured (the substrate) passes through a thin protective membrane or gel before encountering the biological sensing agent. These outer coatings allow access to the sensing agent, but must provide a degree of stability and minimize fouling of the device. The sensing agent is normally an enzyme or an antibody, but improved cell immobilization methods mean that in some cases whole cells can be used. Substrate and sensor interact, the result of which is detected as a change in electrical capacitance or conductance. It may be a temperature change, a mass or optical change, the production of a gas, or a new chemical that is detected. An appropriate transducer is then used to detect and measure the product, resulting finally in an electrical signal, which can be amplified to the required level. In this way an immediate readout can be provided - the biosensor has "sensed" successfully.An example is the use of the immobilized enzyme glucose oxidase, which releases electrons on interaction with glucose. A sensor of this type could detect continuously the level of glucose in the blood - a function of the human pancreas which is deficient in diabetic patients. If coupled with a minipump triggered to respond as required, the functions of a normal pancreas can be restored, giving a maintained, appropriate level of blood insulin - a considerable improvement on the inevitable peaks and troughs experienced by diabetics receiving regular insulin injections.
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