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

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. Graphical This work presents portable paper test strips embedding ascorbic acid (AA)-modified gold nanoparticles for colorimetric Ag + detection. AA reduces Ag + , yielding Ag@Au core-shells that shift the localized surface plasmon resonance (LSPR) and change color. The assay shows high selectivity with anti-interference, linearity ( R 2 = 0.99), UV-vis LOD 0.49 µg mL −1 , naked-eye threshold 6.0 µg mL −1 , and validated tap-water recoveries.