An Electrochemical Sensor for Sensitive Determination of L-cysteine and Its Electrochemical Kinetics on AgNPs/GQDs/GCE Composite Modified Electrode

Abstract

L-cysteine plays an essential role in protecting liver cells from toxic damage and regulating phospholipids in the liver. However, some of the methods used to detect L-cysteine suffer from low sensitivity and multiple steps. Herein, we developed a high-sensitivity electrochemical sensor which was manufactured by electrodepositing silver nanoparticles (AgNPs) on a glassy carbon electrode (GCE) modified with graphene quantum dots (GQDs) for detecting L-cysteine. GQDs and AgNPs as electrode modifications were applied to amplify the active area and enhance electron-transport ability for magnifying the sensor signal. Fourier transform infrared (FTIR), X-ray diffraction (XRD) and Raman spectra were used for characterization of GQDs. Field emission scanning electron microscopy (FESEM) was applied to characterize AgNPs. Cyclic voltammetry (CV), differential pulse voltammetry (DPV), chronocoulometry (CC), electrochemical impedance spectra (EIS) were employed to investigate the electrochemical and kinetic behaviors of L-cysteine on composite modified electrode, we focused on discussing the kinetic parameters, such as active areas (A), diffusion coefficient (D), proton transfer number (m), standard rate constant (k) and electron transfer coefficient (α). These experimental conditions such as pH and detection rate had been optimized. Under the optimized conditions, the DPV response of the composite electrode to L-cysteine was obtained in the concentration from 2 × 10−4 to 1 × 10−7 mol/L with a lower detection limit of 1 × 10−8 mol/L. Moreover, composite electrode displayed brilliant specific recognition ability to L-cysteine, which prevented the interference from other compounds (e.g., L-tryptophan, ascorbic acid, aneurine hydrochloride), and common ions (K+, NH4+, Cl−, NO3−). In addition, the sensor has some unique advantages, such as excellent reproducibility, good stability, high sensitivity and could become a promising strategy of detecting L-cysteine.