Application of a simple copper(ii) complex compound as an epinephrine selective voltammetric sensor in the presence of uric acid under aqueous conditions

Developing sensors with high sensitivity and selectivity for detecting neurotransmitters under near-physiological conditions is a major challenge and is crucial for preventing diseases of the nervous, cardiovascular, and endocrine systems. Most existing systems that meet these requirements involve either complicated synthesis processes, require sulfur groups, or are not functional under aqueous conditions. Herein, we report that the self-organisation of a simple imine ligand L with copper(II) tetrafluoroborate leads to the formation of a [CuL₂](BF₄)₂ complex (CuL₂) with a 2 : 1 ligand-to-metal ratio, as confirmed by high-resolution electrospray ionization mass spectrometry (HR ESI-MS), Fourier-transform infrared (FT-IR) spectroscopy and single-crystal X-ray analysis. Surprisingly, modifying a gold surface with a self-assembled monolayer of the CuL₂ complex created a stable sensor for selective detection of epinephrine (EP) using differential pulse voltammetry (DPV) in phosphate buffer solution (PBS) at pH 7.0. A linear correlation between the current response and the concentration of EP was observed with a detection limit of 0.03 μM, high reproducibility and good stability in the range of 0.0001 to 0.875 mM. These results show that the new sensor (Cu/Au) can serve as a reliable analytical tool to selectively detect EP alone and in a mixture with coexisting uric acid (UA) in tested samples.