INVESTIGATION OF THE EFFECTS OF POLAR ORGANIC-SOLVENTS ON THE ACTIVITY OF TYROSINASE ENTRAPPED IN A POLY(ESTER-SULFONIC ACID) POLYMER

The behaviour of an amperometric organic-phase phenol sensor was inves tigated in acetonitrile, acetone and tetrahydrofuran reaction media co ntaining 20% v/v water. The biosensor consisted of tyrosinase immobili sed on a Pt or glassy carbon electrode in a poly(estersulphonic acid) polymer matrix. Analyses of the results of the cyclic voltammograms of the enzyme electrode in the presence of 100 mu M phenol show that the sensor is effective in the three solvent media. The normalised cataly tic currents (I-k,I-normalised) Of the sensor in the three solvents ar e 35.5, 26.0 and 8.02, for acetone, acetonitrile and tetrahydrofuran, respectively. I-k,I-normalisied is the ratio of the cyclic voltammetri c reduction current at -150 mV in the presence of 100 mu M phenol to t he background current at the same potential. The steady-state amperome tric results show that the sensor exhibits fast response to phenol, an d the kinetics of the responses agree with the Michaelis-Menten model in all solvent media. The I-max/K-m(app) values show that the phenol s ensor is about five times more sensitive in acetone and acetonitrile t han in tetrahydrofuran. Diffusion coefficient values of phenol (D-phen ol) computed from potential step studies on a 25 mu m Pt microelectrod e are 9.85, 8.80 and 6.34 x 10(-6) (cm2) s(-1), for acetone, acetonitr ile and tetrahydrofuran, respectively. The similarity in the D-phenol values suggests that the flux of the analyte to the electrode surface does not alone determine the sensitivity of the tyrosinase sensor.