According to the methodology described in the SI file, section S5.1, a series of k and D values was estimated for SPCE, as represented in Table . According to the obtained results, the modified Berzins-Delahay equation describes the system well, as reflected in the fitted parameters, i.e. the R 2 , the chi 2 values and the negligible standard errors of each calculated quantity (see SI file, section S5.2). For simplicity, it was assumed that the D of the reduced and oxidized forms of the redox probes are equal. The CS-coated SPCE exhibits lower D for [Fe(CN)6] 3-/4-compared to the bare SPCE, indicating that redox species diffuse into the hydrogel at lower rates compared to the PBS solution. This can be correlated to the electrostatic attraction between positively charged CS chains and [Fe(CN)6] 3-/4-species that retard their acceleration in the electric field. Part of negatively charged [Fe(CN)6] 3-/4-species, which diffuse through free volumes between positively charged polymeric chains are attracted by local electric fields around NH3 + moieties on CS chains that oppose the electric field of electrode, decreasing the speed of the redox probes. However, the improved equilibrium absorption of negatively charged redox species likely led to enhanced partitioning and heightened permeability across the hydrogel membrane . The diffusivity and partitioning of penetrants tend to have opposing effects that counteract each other.