Microbial sensors result from the combination of a microorganism with a transducer capable of detecting the metabolite involved. Microorganisms possess enzymatic systems that effect biological transformations. The immobilization of microorganisms on transducers is thus a logical step in the construction of biosensors. This approach is attractive because it eliminates extraction and purification processes, and because the enzyme is maintained in its natural environment thus avoiding problems like the regeneration of cofactors. Microorganisms are often immobilized by physical entrapment in gels, or using dialysis membranes, as described in § 3.3.2. The transducers employed in enzyme sensors are also used here. Potentiometric or amperometric electrodes (pCO2, pNH3, pO2) are particularly useful because they already have a gas-permeable hydrophobic membrane (teflon or silicone). The microorganism is inserted between this membrane and a microporous or dialysis membrane. In contrast to enzymes, once the microorganism is immobilized it must be kept in a basal culture medium so as to maintain its activity.
KeywordsBiological Oxygen Demand Lipoic Acid Enzyme Electrode Carbamic Acid Acetobacter Xylinum
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