Colorimetric Detection of Ag + by Using Ascorbic Acid‐Modified Gold Nanoparticle Test Strips

Abstract Silver is widely used in daily life and industry, resulting in environmental release and potential health risks from toxic silver ions (Ag + ). In this study, a paper‐based colorimetric sensing strategy utilizing ascorbic acid (AA)‐modified gold nanoparticles (AA@AuNPs) was developed for the rapid and portable detection of silver ions in various aqueous matrices. Under optimized conditions, AA coordinates the AuNP surface and promotes the formation of an Ag@Au core–shell upon exposure to Ag+, yielding a distinct colorimetric response. The sensing mechanism and surface chemistry were validated by dynamic light scattering (DLS), transmission electron microscopy (TEM), zeta potential analysis, Fourier‐transform infrared spectroscopy (FT‐IR), and UV–visible (UV–vis) spectrophotometry. High specificity toward Ag + with strong anti‐interference in the presence of common coexisting ions was demonstrated, and a combined‐interference test confirmed negligible cross‐reactivity. Quantitatively, excellent linearity ( R 2 = 0.99) was achieved, with a UV–vis detection limit of 0.49 µg mL −1 and a naked‐eye detection threshold of 6.0 µg mL −1 . The paper strips enabled Ag + capture for post‐analysis recovery and safe disposal, reducing secondary pollution relative to solution‐based assays. The platform is simple, low‐cost, and field‐deployable, and validation in tap‐water samples with reliable recoveries underscores its potential for on‐site Ag + monitoring.