Electrochemical determination of tryptophan using a glassy carbon electrode modified with flower-like structured nanocomposite consisting of reduced graphene oxide and SnO2

A nanocomposite consisting of reduced graphene oxide (rGO) decorated with tin oxide (SnO2) nanoparticles was fabricated using a hydrothermal route. Cyclic voltammetry showed that a glassy carbon electrode (GCE) modified with the rGO/SnO2 composite exhibited an excellent electrocatalytic activity towards the oxidation of amino acid tryptophan (Trp) in 0.1 M phosphate buffer solution (pH = 7). The combined use of rGO and SnO2 results in higher current response and lower oxidation potential (0.76V) compared to those of a bare GCE, SnO2/GCE, and rGO/GCE. Differential pulse voltammetry study showed a linear relationship to the Trp concentration of 1-100 mu M. The low detection limit of Trp was identified at 0.04 mu M (S/N = 3) with sensitivity of 37.3 mu A mu M-1 cm(-2). The sensor demonstrated an excellent selectivity, good stability, and reproducibility. The sensor was applied to the determination of Trp in spiked milk and amino acid injection samples by the standard addition method and gave recoveries of 98.0-101.3% and 98.1-102.5%, respectively. (C) 2016 Elsevier B.V. All rights reserved.