Exploration of Biocompatible Ascorbic Acid Reduced and Stabilized Gold Nanoparticles, as Sensitive and Selective Detection Nanoplatform for Silver Ion in Solution

Silver ion (Ag⁺) is one of the heavy metals (HMs) of interest that must be regularly profiled, by virtue of its toxicity and eco-physiological implications. Herein, a colorimetric assay for sensitive detection of Ag⁺ ion in solution is developed. To avoid the introduction of toxic chemicals in the material synthesis stage, ascorbic acid (AA) was employed as the reducing/stabilizing agent at room temperature (RT), for the gold nanoparticle (AuNPs) synthesis. The biocompatibility of the synthesized AA-AuNPs was demonstrated by the cytotoxicity test using MTT assay on mouse macrophage cells (RAW 264.7), which revealed that AA-AuNPs imparted no destruction on the tested cells. Further, AA capping on the AuNP surfaces was confirmed by Raman and Fourier transform infrared spectroscopy (FTIR). At the optimal detection conditions, the addition of Ag⁺ to AA-AuNPs solution (pH 10) resulted in naked-eye color transitions from red to orange and yellow, with a blue shift in the absorption maximum from 522 to 400 nm. This is attributed to the reduction of Ag⁺ on the initially synthesized AA-AuNPs probe, induced by the capping agent, forming Au@Ag core–shell nanomaterials. The analytic response (A_f-A₀)400 nm plotted against Ag⁺ concentrations was linear within 0.05–12.50 and 12.50–150.00 µM, with estimated limit of detection (LOD) of 15.8 nM. For practical usage, the probe was deployed for Ag⁺ detection in lake water sample, showing impressive accuracy (95.5–104.7%) and precision.