Instrumentation and Control Systems 677 sensors measuring specific biomolecular interactions. The basic principle is first to immobilize one of the interacting molecules, the ligand, onto an inert substrate such as a dextran matrix which is bonded (covalently bound) to a metal surface such as gold or platinum. This reaction must then be converted into a measurable signal typically by taking advantage of some transducing phenomenon. Four popular transducing techniques are Potentiometric or amperometric, where a chemical biological reaction produces a potential difference or current flow across a pair of electrodes Enzyme thermistors, where the thermal effect of chemical or biological reaction is transduced into an electrical resistance change Optoelectronic, where a chemical or biological reaction evokes a change in light transmission Electrochemically sensitive transistors whose signal de- One example is the research(I to produce a biomedical device which can be implanted into a diabetic to control the flow of insulin by monitoring the glucose level in the blood via an electrochemical reaction. One implant able glucose sensor, designed by Leland Clark of the Childrens Hospital Research Center in Cleveland, utilizes a microprobe where the outside wall is constructed of glucose-permeable membrane such as cuprophan. Inside, an enzyme which breaks the glucose down to hydrogen peroxide is affixed to an inert substrate. The hydorgen peroxide then passes through an inner membrane, constructed of a material such as cellulose acetate, where it reacts with platinum producing a current which is used to monitor the glucose A commercial example of a biosensor, introduced by pharmacia Biosensor AB2, is utilizing a photoelectric principle called surface plasmon resonance(SPR)for detection of changes in concentration of macromolecu r reactants. This principle relates the energy transferred from photons bombarding a thin gold film at the resonant angle of incidence to electrons in the surface of the gold. This loss of energy results in a loss of reflected light at the resonant angle The resonant angle is affected by changes in the mass concentration in the vicinity of the metal's surface which is directly correlated to the binding and dissociation of interacting moleculesInstrumentation and Control Systems 677 sensors measuring specific biomolecular interactions. The basic principle is first to immobilize one of the interacting molecules, the ligand, onto an inert substrate such as a dextran matrix which is bonded (covalently bound) to a metal surface such as gold or platinum. This reaction must then be converted into a measurable signal typically by taking advantage of some transducing phenomenon. Four popular transducing techniques are: Potentiometric or amperometric, where a chemical or biological reaction produces a potential difference or current flow across a pair of electrodes. Enzyme thermistors, where the thermal effect of the chemical or biological reaction is transduced into an electrical resistance change. Optoelectronic, where a chemical or biological reaction evokes a change in light transmission. Electrochemically sensitive transistors whose signal de￾pends upon the chemical reactions underway. One example is the research['] to produce a biomedical device which can be implanted into a diabetic to control the flow of insulin by monitoring the glucose level in the blood via an electrochemical reaction. One implant￾able glucose sensor, designed by Leland Clark of the Childrens Hospital Research Center in Cleveland, utilizes a microprobe where the outside wall is constructed of glucose-permeable membrane such as cuprophan. Inside, an enzyme which breaks the glucose down to hydrogen peroxide is affixed to an inert substrate. The hydorgen peroxide then passes through an inner membrane, constructed of amaterial such as cellulose acetate, where it reacts with platinum producing a current which is used to monitor the glucose concentration. A commercial example of a biosensor, introduced by Pharmacia Biosensor AB2, is utilizing a photoelectric principle called sufluceplusmon resonance (SPR) for detection of changes in concentration of macromolecu￾lar reactants. This principle relates the energy transferred from photons bombarding a thin gold film at the resonant angle of incidence to electrons in the surface of the gold. This loss of energy results in a loss of reflected light at the resonant angle. The resonant angle is affected by changes in the mass concentration in the vicinity of the metal's surface which is directly correlated to the binding and dissociation of interacting molecules