Analysis of Melatonin Using a Poly(L-Tyrosine)-Modified Graphene Paste Electrode

In this work, a novel modified graphene paste electrode (P(L-TY)/MGPE) was developed through polymerization of L-tyrosine (L-TY) and was used for electrochemical detection of melatonin (MLT). Its oxidation peak was observed at 0.349 V, with the corresponding current response of 8.46 mu A in 0.2 M phosphate-buffered saline (PBS) solution at pH 1.0. Scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV) were employed to study the electrochemical behavior of the P(L-TY)/MGPE and bare graphene paste electrode (BGPE). The sensor demonstrated strong resistance to interference from various metal ions and organic molecules. A scan rate study suggested that the oxidation process followed an adsorption-based mechanism. The effects of pH and concentration were also investigated. The modified electrode achieved a detection limit of 0.5 x 10-6 M and a quantification limit of 1.6 x 10-6 M. Additionally, P(L-TY)/MGPE demonstrated excellent stability, reproducibility, and repeatability. The sensor was successfully applied for analysis of a real sample of pharmaceutical tablets, confirming its reliability for melatonin detection in commercial formulations.