An electrochemical sensor for determination of tryptophan in the presence of DA based on poly(L-methionine)/graphene modified electrode

A glassy carbon electrode modified with poly(L-methionine) and graphene composite film (PLME/GR/GCE) was fabricated by electropolymerization for determination of L-tryptophan (L-Trp) in the presence of dopamine (DA). The morphology and structure of the composite film were investigated by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy and electrochemical impedance spectroscopy (EIS). Differential pulse voltammetry (DPV) was utilized to investigate the electrocatalytical oxidation of L-Trp from the potentially interfering species on the PLME/GR/GCE. Under optimum conditions, the proposed method exhibited a wide linear dynamic range 0.2–150 μM, with a detection limit (S/N = 3), and good reproducibility and high selectivity. Moreover, the proposed modified electrode has been successfully applied to determine L-Trp in milk and human serum samples.