Fig. 1
(a) Schematic diagram of the 4-electrode setup: two platinum wires functioned as working and counter electrodes, while two Ag/AgCl/3 M KCl electrodes were used as sensing and reference electrodes; (b) Equivalent circuit model of the skin membrane, where Rsol represents the resistance of the donor and receptor solutions, Rmem is the membrane resistance, and CPE is a constant-phase element used to determine the effective capacitance of the membrane Ceff.
