Highly Selective Voltammetric Sensor for l‑Tryptophan Using Composite-Modified Electrode Composed of CuSn(OH)6 Microsphere Decorated on Reduced Graphene Oxide

In this study, a nanostructured CuSn­(OH)6 microsphere decorated on reduced graphene oxide (CSOH/rGO) was prepared by a co-precipitation method followed by ultrasonication, which was used for the sensitive and selective determination of l-Tryptophan (l-Trp) in the presence of uric acid. Its structure and morphology were characterized by X-ray diffraction (XRD), field emission scanning/transmission electron microscopy (FE-SEM/TEM), Fourier transform infrared (FT-IR) spectroscopy, Brunauer–Emmett–Teller (BET) analysis, and X-ray photoelectron spectroscopy (XPS). Galvanostatic charge/discharge tests, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and differential pulse voltammetry (DPV) methods have also been employed to investigate the electrochemical performance of the CSOH/rGO composite. Analytical parameters such as loading amount of catalyst, scan rate, pH value, cyclic stability, repeatability, and reproducibility were optimized. The CSOH/rGO composite shows excellent detection of l-Trp in a wide dynamic linear range (WLR) of 0.05–175.8 μM, a low limit of detection (LOD) of 2.0 nM, a limit of quantification (LOQ) of 68.9 nM, and a sensitivity of 0.21 μA μM–1 cm–2. The fabricated electrode was further used to monitor the selectivity of l-Trp in the presence of uric acid and applied to the detection of l-Trp in spiked real samples with satisfactory results.