2.3. CSE surface activation
The activation procedure of a pure CSE surface was carried out by using ultrasonic irradiation and cyclic voltammetry techniques. Before activation, an electrode surface was polished with 0.3 and 0.05 μm alumina powders to mirror like. The polished electrode was ultrasonically irradiated subsequently in anhydrous ethanol for 3 min and doubly distilled water for 2 min. Then, it was dried with highly purified nitrogen gas in air. The pre-treated CSE was electrochemically activated in 0.1 M HClO4 by scanning potential in the range of (0.0 to +1.5) V for 20 cycles (voltage scan rate v, 50 mV/s). Further, this electrode was scanned between +0.2 to +1.4 V in 0.1 M PBS until a steady-state current–voltage curve was obtained. The activated CSE was stored in air at room temperature.