Fig. 4. (a) Cyclic voltammograms of the aptamer functionalized NPG electrode in 0.02 M PBS (pH 5.5) at a scan rate of 50 mV s⁻¹ before (dashed, black line) and after DHBA immobilization (solid, red line), (b) SWV curves obtained for the proposed aptasensor in 0.02 M PBS, pH 5.5, before (dashed, red line) and after challenging with 1 μM cocaine (solid, blue line), the effect of incubation time (c), frequency (d), pulse width (e) and amplitude (f) on the SWV response of the aptasensor toward cocaine.