Article ID: 2025.011
The surface area of gold nanoparticles (AuNPs) was estimated through the adsorption of cysteine onto the AuNPs. The AuNPs used were synthesized by a solution plasma process and were polycrystalline. Capillary zone electrophoresis (CZE) was employed to monitor the cysteine adsorption. An AuNP dispersed solution with cysteine adsorption was directly introduced into the CZE system, and a broad peak was obtained in the electropherograms with the dispersed AuNPs. Shot signal for the aggregated AuNPs was not detected in the electropherograms, indicating that the dispersion of the AuNPs was maintained even after the cysteine adsorption. The effective electrophoretic mobility of the AuNPs was reduced by the adsorption of cysteine to the AuNP surface. Any peak attributed to the cysteine was not detected at low concentrations of the cysteine, and the added cysteine was mostly adsorbed onto the AuNPs. An additional peak attributed to the residual cysteine was detected at higher concentrations of cysteine from 100 μmol L−1, and a linear relationship was obtained between the concentration of cysteine and the peak area of the cysteine with an x-intercept at 86 μmol L−1. This concentration represents the saturation point of surface adsorption onto the AuNPs. The surface area of the AuNP dispersed solution was estimated from the adsorption amount of cysteine and the cross-section area of a cysteine molecule, resulting in an estimated surface area of 0.078 m2 mL−1. The estimated surface area was also verified through the adsorption of glutathione onto the AuNP.
