Cu-modified carbon paste electrode as a sustainable approach for electrochemical determination of insulin

: A novel and environmentally sustainable approach was used to fabricate carbon paste electrodes for insulin determination. In this work fully eco-friendly components for electrochemical sensors for insulin determination were used. The carbon material was derived from waste processing, while other components, including coconut oil as a binder and a pencil lead as a conductive contact for carbon paste electrode, were chosen for their eco-friendly nature. The prepared electrode was subsequently modified with copper via two simple methods, yielding two distinct electrode materials: a Cu-modified electrode (using cyclic voltammetry method) and a Cu 2 O-modified electrode (using pulse deposition method). Both materials were electrochemically studied and compared for insulin detection. It was found that the electrochemical performance was limited by different factors - adsorption for CV-Cu/CPE and charge transfer kinetics for 15pCu/CPE. Notably, the formation of a specific Cu(II)-insulin complex at the CV-Cu/CPE electrode surface led to superior performance. Linear range of insulin concentrations was within 5 nM to 4 μM, with the sensitivity 1.13 mA/μM and a low detection limit (LOD) of 5 nM in PBS, while a LOD of 0.7 μM was achieved in blood serum. This sensor demonstrated excellent selectivity in the presence of common electrochemically active species and achieved high reproducibility, with a relative standard deviation (RSD) below 10%. The results suggest that this sustainably fabricated CV-Cu/CPE sensor is a promising and effective tool for insulin detection also in real samples.