A new colorimetric assay based on an assembly of gold nanoparticles and gold nanoclusters for Ag+ and l-cysteine detection

Abstract

This study reports a novel colorimetric assay for Ag⁺ and L-cysteine (L-Cys) detection by Ag⁺-mediated aggregation of gold nanoparticles (AuNPs) and gold nanoclusters (AuNCs). L-Histidine-stabilized AuNCs (His@AuNCs) and EDTA-stabilized AuNPs (EDTA@AuNPs) were synthesized. Upon introduction of Ag⁺, the induced aggregates of AuNCs–Ag⁺–AuNPs resulted in a distinct color shift from red to blue. Quantitative analysis showed that the absorbance ratio of the aggregated system was linearly correlated with the concentration of Ag⁺ (8–20 μM) (R² > 0.998), and the recovery rate was 97.6–103.1% in river water samples. The –SH of L-Cys competitively complexed with Ag⁺, effectively disintegrating the nanomaterial aggregates and restoring the solution color and absorption spectra. A standard curve of 1–7 μM with recovery rates of 97.5–106.7% was established, enabling the quantification of L-Cys in milk. The developed method features simple operation, high sensitivity, and good selectivity, providing new ideas for detecting metal ions and biomarkers using gold nanomaterials.