Impact of post-deposition curing of graphite thick-film working electrode on the performances of electrochemical sensors

Miniature electrochemical sensors (ES) with screen-printed electrodes and electrical contacts offer qualitative and quantitative detection of various redox-active compounds in water rapidly, with good sensitivity and selectivity. To avoid short circuits, herein we covered the electrical contacts with UV- and temperature-curable polymers to isolate them from the solution. We investigated the influence of UV-light exposure and thermal treatment at 150 °C in air on the surface morphology, chemical composition and electrical conductivity of graphite-based working electrode (WE), as well as on overall electrochemical performance of the ES. Untreated (AP), UV-, and temperature-cured WE possess comparable surface roughness and sheet resistance, 3 μm and 9 Ω/sq., respectively. Cyclic voltammetry (CV) reveals good reversibility for all electrodes, with AP and UV-cured WEs having comparable peak separation (≈115 mV), current response, electrochemically active surface area A ecsa (0.64 cm 2 ), and electron transfer rate constant k 0 (8.0 × 10 −3 cm s −1 ). Heating to 150 °C in air increased peak separation to 170 mV, reduced A ecsa and k 0 to about 27 % and 22 %, attributed to oxygen incorporation in WE, confirmed by X-ray photoelectron spectroscopy. The analysis of ESs in aqueous solution of insecticide imidacloprid confirmed similar responses of AP and UV-cured ESs, whereas response of temperature-cured ES was significantly lower. The temperature-cured ESs demonstrated improved electrochemical responses after linear sweep voltammetry in a potential range down to −1.5 V, which is likely due to the removal of oxygen from WE. Our results demonstrate that post-deposition curing significantly influences the performance of electrochemical sensors for water pollution monitoring. • Protective coating of electrical contacts requires post-deposition heating or UV-curing of SPEs. • Surface morphology and sheet resistance are similar for as-prepared and post-deposition cured graphite electrodes. • Heating to 150 °C in air reduces SPE response due to oxidation of graphite electrode. • Linear voltage scan to −1.5 V improves response of heated SPE by minimising oxygen groups in graphite. • UV curing effectively preserves the performances of the electrode.