PERFORMANCE OF A THERMAL BIOSENSOR IN ORGANIC-SOLVENTS

The use of organic solvents as media for enzymic reactions presents many interesting possibilities in preparative as well as analytical work. The solubility of hydrophobic enzyme substrates is higher in organic solvents than in water. Enzyme reactions could take different routes in organic solvents to those which occur in water; the direction of a reaction can even be reversed. In addition, substrate specificity may be altered. The activity of enzymes in organic media may be as high as in aqueous media and the enzyme stability is sufficient for practical work. This paper describes the use of a thermal assay probe (TAP), or enzyme thermistor, to measure the heat produced by immobilized enzymes in a continuous flow of organic solvents or water-solvent mixtures. The temperature response of the TAP is dependent on the enthalpy change of the reaction and of the heat capacity of the system. Since the specific heat of organic solvents is up to three times lower than that of water, it should be expected that the sensitivity of the TAP could be increased by performing the assays in organic media. It was found that even rather small amounts of alcohols (5% vol./vol.) in the buffer approximately doubled the temperature response for glucose oxidase and catalase. The heat production by peroxidase was as much as 45 times higher in toluene compared to buffer. The advantages of increased substrate solubility in organic solvents was demonstrated by operating a lipase column in cyclohexane. All enzymes studied showed good stability in the organic solvents used. © 1990.