Spherical Silver Nanoparticles Located on Reduced Graphene Oxide Nanocomposites as Sensitive Electrochemical Sensors for Detection of L-Cysteine

Abstract

A new, simple, and effective one-step reduction method was applied to prepare a nanocomposite with spherical polycrystalline silver nanoparticles attached to the surface of reduced graphene oxide (Ag@rGO) at room temperature. Equipment such as X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR) was used to characterize the morphology and composition of the Ag@rGO nanocomposite. A novel electrochemical sensor for detecting L-cysteine was proposed based on fixing Ag@rGO onto a glassy carbon electrode. The electrocatalytic behavior of the sensor was studied via cyclic voltammetry and amperometry. The results indicate that due to the synergistic effect of graphene with a large surface area, abundant active sites, and silver nanoparticles with good conductivity and high catalytic activity, Ag@rGO nanocomposites exhibit significant electrocatalytic activity toward L-cysteine. Under optimal conditions, the constructed Ag@rGO electrochemical sensor has a wide detection range of 0.1-470 μM for L-cysteine, low detection limit of 0.057 μM, and high sensitivity of 215.36 nA M^-1 cm^-2. In addition, the modified electrode exhibits good anti-interference, reproducibility, and stability.

Keywords: L-cysteine; detection; electrochemical sensor; graphene; nanocomposite.

Figure 1

SEM image (a), XRD pattern (b), and EDX spectrum (c) of Ag@rGO.

Figure 2

TEM images of GO (a) and Ag@rGO (b); HRTEM image (c) and SAED pattern (d) of Ag@rGO.

Figure 3

XPS spectra of rGO and Ag@rGO: (a) High-resolution deconvoluted scan spectra of C 1s, (b) Scan spectra of O 1s, (c) Survey scan and (d) High-resolution scan spectra of Ag 3d.

Figure 4

FTIR spectra of GO (red curve) and Ag@rGO nanocomposite (blue curve).

Figure 5

Electrochemical impedance spectroscopy (EIS) of bare GCE, rGO/GCE, Ag@rGO/GCE under 5.0 μM K₃Fe(CN)₆/K₄Fe(CN)₆ (1:1).

Figure 6

CV curves of 50 μM L-cysteine on bare GCE, rGO/GCE, and Ag@rGO/GCE in 0.1 M phosphate-buffered solution (pH = 7.0). Scanning rate: 100 mV s⁻¹.

Figure 7

Effect of scanning rate on the voltammograms of Ag@rGO/GCE in pH = 7.0 phosphate-buffered solution at 20, 40, 60, 80, 100, 120, 140, 160, and 180 mV s⁻¹. Inset: Plot of the peak currents (I) vs. square root of the scanning rate.

Figure 8

Cyclic voltammograms of electro-oxidation of 50 μM L-cysteine in 0.1 M PBS at different pH: 5.0, 6.0, 7.0, 8.0, 9.0. Scanning rate: 100 mV s⁻¹.

Figure 9

Amperometric responses at Ag@rGO/GCE with successive additions of L-cysteine in 0.1 M phosphate-buffered solution (pH = 7.0). Inset: Plots of enlarged curves showing the addition of 0.1–1 μM of L-cysteine and the corresponding calibration curve.

Figure 10

Amperometric response observed following additions of 50 μM L-cysteine and 200 μM various interfering substances.

Figure 11

Reproducibility and stability of Ag@rGO/GCE for L-cysteine determination; the error bars illustrate the standard deviations of three independent measurements.