Electrocatalytic oxidation of thiocholine at chemically modified cobalt hexacyanoferrate screen-printed electrodes

In this work, cobalt hexacyanoferrate (CoHCF) modified screen-printed electrodes were developed and characterised electrochemically. The effect of different cations was investigated showing a more reversible system with a well-defined peak around +0.35 V vs. Ag/AgCl when Na+ was used as cation in the supporting electrolyte. The transfer coefficient (α) and the apparent charge transfer rate constant (ks) for electron transfer between the electrode and the CoHCF layer was calculated. The electrocatalytic behaviour of CoHCF towards oxidation of enzymatically generated thiocholine was thoroughly investigated. Cyclic voltammetry experiments performed in thiocholine solution showed the classical shape of a mediated redox system. The diffusion constant of thiocholine was estimated using chronoamperometry. Also, the catalytic rate constant k of thiocholine at CoHCF–SPE was determined. The current due to thiocholine mediated oxidation was then evaluated in batch amperometric mode at +0.5 V vs. Ag/AgCl obtaining a linear range (5 × 10−7–1 × 10−5 mol L−1) with a low detection limit and a high sensitivity equal to 5 × 10−7 mol L−1 and 435 mA mol−1 L cm−2, respectively.