2.2. Electrochemical preparation of enzyme electrode
Enzyme electrode was prepared by one-step potentiostatic polymerization in 50 mM PBS (pH 6.5) containing 10 mM EDOT, 50 mg L1 AO, 20 mM SLS, and 10 mM LiClO4 at an applied potential of 1.10 V vs. Ag/AgCl for 90 s in a one-compartment three-electrode cell (Scheme 1). A bare Pt disk electrode with a diameter of 3 mm served as the working electrode, and a stainless steel wire with a diameter of 1 mm was used as the counter electrode. The reference electrode was an Ag/AgCl electrode with a diameter of 0.5 mm. They were placed 5 mm apart during the electrochemical measurements. The counter electrode was carefully polished with abrasive paper (1500 mesh), cleaned successively with water and acetone, and then dried in air before each experiment. The Pt disk electrode was polished with alumina (Al2O3, 0.05 lm), rinsed with deionized distilled water and cleaned ultrasonically, and then dried in air before each experiment. All solutions (except for solutions containing VC) were deoxygenated by bubbling with dry argon for 10 min prior to each experiment. All experiments (except for solutions containing VC) were performed under slight argon overpressure. Unless otherwise stated, the temperature was kept at 25 degrees Celsius (C). AO molecules were immobilized in PEDOT-LS film during electropolymerization. Enzyme electrode was washed repeatedly with double-distilled deionized water to remove loosely bound enzyme, electrolyte, and monomer from the surface. And then enzyme electrode was stored in PBS at 4 C prior to use.