DETECTION OF HEAVY-METAL SALTS WITH BIOSENSORS BUILT WITH AN OXYGEN-ELECTRODE COUPLED TO VARIOUS IMMOBILIZED OXIDASES AND DEHYDROGENASES

Immobilized oxidases were bound on the surface of an affinity membrane and mounted on an oxygen electrode. These biosensors were used for he avy metal salt measurements. After immobilization of the enzymes, firs t order kinetics of inactivation were observed. Surface immobilization increases the sensitivity by a factor of 10, compared to reticulation of the enzyme in a gelatin matrix. After immobilization, 50% inactiva tion was observed with 20 muM HgCl2 for L-glycerophosphate oxidase and 50 nm for pyruvate oxidase. Restoration of activity after HgCl2 treat ment is feasible, but neither complete nor reproducible. To reuse the biosensor, L-lactate dehydrogenase (LDH) from rabbit muscle in solutio n was coupled to immobilized L-lactate oxidase (insensitive to heavy m etal salts). LDH (particularly inexpensive) was replaced after each me asurement. The I50 in phosphate buffer was 1 muM for HgCl2 and 0.1 muM for AgNO3; with other heavy metal salts, no inhibition was observed b elow 500 muM. In Tris buffer, the I50 was 10 muM for CdCl2 and ZnCl2, 50 mum for Pb-acetate and 250 muM for CuSO4. The use of different enzy mes and buffers may allow measurement of specific heavy metal salts.