Reagentless Tyrosinase Enzyme Electrodes: Effects of Enzyme Loading, Electrolyte pH, Ionic Strength, and Temperature

We have prepared a reagentless enzyme activity sensor based on the mediated reduction of oxygen by tyrosinase coimmobilized in an osmium redox polymer hydrogel on glassy carbon electrode surfaces. The activity of this sensor is shown to be influenced by the enzyme loading, yielding an optimum activity for 41.7% (w/w) enzyme in the deposition solution. The electroyte pH, ionic strength, and temperature also affect the electrode response by altering enzyme activity, charge transport rates, and mediator concentration in the films. The response of the sensor decreases by only 25% over a 6-h period. However, reproducible inhibition curves can be obtained by normalization of the sensor response. The resulting enzyme inhibition biosensor can detect levels of the enzyme inhibitor, azide, as low as 1.0 x 10^-5 mol/dm3 in solution. The immobilized sensors can be utilized for the detection of modulators of tyrosinase enzyme activity, such as respiratory poison inhibitors.