Label-Free Colorimetric Detection of Cadmium Ions in Rice Samples Using Gold Nanoparticles

A simple and label-free colorimetric method for cadmium ions (Cd2+) detection using unmodified gold nanoparticles (AuNPs) is reported. The unmodified AuNPs easily aggregate in a high concentration of NaCl solution, but the presence of glutathione (GSH) can prevent the salt-induced aggregation of AuNPs. When Cd2+ is added to the stable mixture of AuNPs, GSH, and NaCl, Cd2+ can coordinate with 4x GSH as a spherical shaped complex, which decreases the amount of free GSH on the surface of gold nanoparticles to weaken the stability of AuNPs, and AuNPs will easily aggregate in high-salt conditions. On the basis of the mechanism, we design a simple, label-free colorimetric method using AuNPs accompanied by GSH in a high-salt environment to detect Cd2+ in water and digested rice samples.