A Redox-Active Copper Complex for Orthogonal Detection of Homocysteine Involving Fluorescence and Electrochemical Techniques.

The present work reports the synthesis, characterization, and excited state photo-physical studies of two copper(II) compounds, 1 & 2, which show interference-free emission with homocysteine (Hcy). Cu(II) complexes offer an orthogonal detection strategy involving fluorescence and electrochemical methods, paving the way for improved point-of-care diagnostics and early cardiovascular diseases intervention. The reduction-induced emission enhancement (RIEE) of Cu complexes facilitates the fluorescence measurement of Hcy at physiological pH. The fluorogenic redox-active 1 and 2 are deposited onto gold electrode surfaces to construct the electrochemical sensors 1@Au and 2@Au, respectively. Under specific alkaline conditions, a distinct and selective redox peak at 0.6 V (vs Ag/AgCl) emerges for 1@Au upon interaction with homocysteine. Further, square wave voltammetry confirms the non-interference of its congener (cysteine) even at high concentrations (200 µM) while detecting Hcy (5-100 µM), demonstrating its potential for real-world applications. The fabricated 1@Au exhibits excellent sensitivity of 31.88 µA/µM, with an impressive detection limit of 2.26 nM, and a limit of quantification of 6.85 nM toward Hcy. The analytical applicability of the 1@Au is validated by quantifying Hcy levels in human blood plasma samples. The results highlighted the feasibility of the proposed technique as a rapid and portable monitoring of Hcy in diagnosing cardiovascular diseases (CVDs).