Visual and Spectroscopic Detection of Arsenic(III) Using Cysteamine-Functionalized Gold Nanoparticles

Herein, we report a colorimetric and spectroscopic sensing strategy for arsenic(III) based on cysteamine-functionalized gold nanoparticles. These nanoparticles, which are readily synthesized from commercially available precursors, are cationic under environmentally relevant conditions and interact with arsenic(III)-derived species under basic sensing conditions via favorable electrostatic interactions. Such interactions directly lead to nanoparticle aggregation, which is accompanied by marked spectroscopic and observable colorimetric changes. The resulting nanoparticle sensor platform is highly sensitive (single ppb-level limits of detection), selective (no response to nonarsenic metal ions; weak response to arsenic(V)), and retains its arsenic(III)-specific response in real-world water matrices as well as in solid-supported formats (PVDF filter membranes). Control experiments highlight the critical role of the cationic cysteamine ligands, and detailed spectroscopic analysis documents the arsenic(III)–ligand interactions underlying the observed response. Collectively, the mechanistic insights established here provide a foundation for extending aggregation-based nanoparticle sensing strategies to other environmentally relevant anionic contaminants.