Synergistic Poly(L-Cysteine–L-Glutamic Acid) Functionalized CuCo2S4 Spinel Nanostructure for High-Performance Voltammetric Determination of Dopamine and Paracetamol in Pharmaceutical and Biological Fluids

A novel electrochemical sensor based on poly(L-cysteine–L-glutamic acid) functionalized CuCo 2 S 4 spinel nanoparticles modified carbon paste electrode (Poly(Cys–Glu)/CuCo 2 S 4 NPs/CPE) was developed for the simultaneous voltammetric determination of dopamine (DA) and paracetamol (PCM). DA is an important neurotransmitter whose imbalance is associated with neurological disorders, while excessive PCM intake can cause severe liver and kidney damage. Therefore, sensitive and reliable determination of these analytes is of considerable clinical and pharmaceutical significance. CuCo 2 S 4 NPs were synthesized via a simple room-temperature co-precipitation method and subsequently functionalized through co-electropolymerization of L-cysteine and L-glutamic acid to create a highly conductive sensing interface. XRD, SEM, and EDX analyses confirmed the successful formation of phase-pure cubic spinel CuCo 2 S 4 NPs with uniform elemental distribution. Electrochemical studies demonstrated that the Poly(Cys–Glu)/CuCo 2 S 4 NPs/CPE exhibited superior electrocatalytic activity toward DA and PCM oxidation compared with bare and singly modified electrodes, owing to the synergistic effect of CuCo 2 S 4 NPs and the polymer film. The fabricated sensor showed well-separated oxidation peaks, wide linear ranges of 0.003–10 µM for DA and 0.005–7.0 µM for PCM, and low detection limits of 0.73 and 1.35 nM, respectively. It also displayed excellent selectivity against common interferents, including ascorbic acid, uric acid, amino acids, carbohydrates, and inorganic ions. In addition, the sensor exhibited good repeatability, reproducibility, and long-term stability. Successful application to pharmaceutical formulations and human serum samples yielded recoveries of 95.7–100.4% with RSD values below 2.30%, highlighting its potential as a sensitive, stable, and cost-effective platform for simultaneous DA and PCM determination.