Heat and drying time modulate the O2 reduction current of modified glassy carbon electrodes with bilirubin oxidases

Abstract

Here we show that the magnitude of the O(2) reduction current of cathodes based on Bilirubin oxidases (BOD) immobilized into a redox hydrogel strongly depends on the drying conditions such as the curing time and temperature of drying as well as the thermostability of the BOD. To illustrate this effect, we performed experiments with two different BODs: one labile BOD from Trachyderma tsunodae and one highly thermostable BOD from Bacillus pumilus with different preparation protocols. The balance between the kinetics of formation of the hydrogel and the enzyme stability leads to optimal drying conditions of 2h at 25°C for both types of BODs when the most widespread protocol uses 18 hours at ambient temperature. For drying times longer than two hours, the catalytic current decreases because of the instability of T. tsunodae. Finally the optimal conditions for BOD from T. tsunodae lead to a faster preparation of electrodes than with the protocol currently in use (2h vs. 18h) and catalytic currents for oxygen reduction 100% higher (1040μA/cm(2) vs. 517μA/cm(2)).