Fig. 3: Cyclic voltammetry results for different electrode architectures.

a CV of 2D Ag/rGO (0 × 0 array) and 3D Ag/rGO (10 × 10 array) electrodes at a fixed scan rate of 0.5 V/s. The CV experiment was carried out in the presence of pbs (50 mm, pH 7.4) added with equimolar concentration (1.0 mm) of ferro/ferricyanide [Fe(CN)₆]^3−/4−mediator. b Effect of chloride (Cl⁻) concentration using CV measurements for 2D Ag/rGO (0 × 0 array) electrode where the Cl⁻ is varied from 30 to 120 mm. Inset of (b) depicts the variation of oxidation/reduction peak currents with Cl⁻ concentrations. The concentration of ferro/ferricyanide was set to 1 mm at a fixed scan rate of 0.5 V/s for this study. Oxidation current is found to be unchanged, but reduction potential showed a minute variation of current, ~2.0 µA, at Cl⁻ concentration of 30–90 mm after which it becomes saturated and stable. The graph in inset (b) corresponds to the median value of three repeated measurements (n = 3). Error bars: median ± SD. c The electrochemical impedance spectroscopy (EIS) responses of 2D Au/rGO (0 × 0 array), 3D Ag/rGO (4 × 4 array), and 3D Ag/rGO (10 × 10 array) for a voltage amplitude of 1 mV as a function of the frequency (1–10,000 Hz). Inset of (c) shows the equivalent electrical circuit diagram to evaluate the charge transfer resistance (R_ct). The EIS/CV experiments were conducted in presence of pbs (50 mm, pH 7.4) containing an equimolar concentration of 1 mm [Fe(CN)₆]^3−/4−. d 3D sensor (10 × 10 array) electrode was used to detect dopamine concentration of 0.1–50 µm and an investigation of cross-reactivity effect was performed in presence of ascorbic acid (AA) (0.1 µm) at a fixed scan rate (0.5 V/s) and Cl^- concentration (120 mm). The results indicate that the current increases with an increase in dopamine concentration at a fixed oxidation potential of −0.14 V.