Enhancing Melatonin Analysis: Unveiling A Novel Polymer-Based Electrochemical Sensor for Human Fluid Matrices and Pharmaceutical Samples

In this study, a polymerized film of bromocresol purple was successfully formed on a glassy carbon electrode using cyclic voltammetry. Several parameters were investigated to optimize the polymerization process. The optimal conditions included 35 potential cycles in a 0.1 M phosphate buffer solution at pH 5.6 containing 0.1 M NaNO₃ and 5.0 × 10^–4M monomer, resulting in a stable poly(bromocresol purple) film on the electrode surface. Cyclic voltammetry and electrochemical impedance spectroscopy were used to characterize the modified electrode. The modified electrode showed a significant improvement in melatonin detection and was successfully applied for its analysis in phosphate buffer solution at pH 8.0. Melatonin was determined over linear ranges of 0.08–60 µM using differential pulse voltammetry, and 0.2–10 and 20–100 µM using square wave voltammetry, with corresponding detection limits of 24.4 and 51.8 nM, respectively. The developed methods were successfully applied to tablet dosage forms, human serum, and artificial urine samples, yielding satisfactory recoveries between 99.36% and 101.06%. The selectivity of the modified electrode was assessed in the presence of potential interfering substances commonly present in human body fluids, with a tolerance limit of ±3.9%. Furthermore, the modified electrode demonstrated excellent reproducibility and long-term stability.