▎ 摘　　要

In this study, a new method is presented for the direct determination of L-tryptophan (Try), using E. tereticornis leave as an environmentally friendly reducing agent for synthesis of reduced graphene oxide/gold nanoparticles (rGO/AuNPs). Scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and Raman spectroscopy analyses showed a uniform distribution of gold nanoparticles on thin layers of reduced graphene oxide. The synthesized nanocomposite was used as a sensitive and electroactive substrate on the surface of screen-printed electrode for electrochemical oxidation of Try in biological samples. Differential pulse voltammetry (DPV) and cyclic voltammetry (CV) showed a reliable analytical signal for the oxidation of Tryptophan at 0.65 V. Response surface methodology (RSM) model was utilized for improving the sensitivity of detection based on central composite design. Under the optimum conditions (Britton Robinson buffer, pH: 6.0; AuNPs/rGO ratio (W/W): 4 and drop casted nanocomposite volume: 5 mu l), the calibration curve of Try is linear between 0.5-500 mu mol/L (R = 0.9976) with detection limit (LOD) and limit of quantification (LOQ) of 0.39 and 1.32 mu mol/L, respectively. In addition, the SPE/rGO/AuNPs electrochemical sensor showed good reproducibility, high sensitivity and good selectivity towards the determination of Try, which makes it suitable for the analysis of Try in human plasma, serum and saliva.