Mechanistic insight into Pb²⁺ sensing by gallic acid-capped gold nanoparticles via SP-ICP-MS and complementary...

Lead (Pb²⁺) contamination in water is a major environmental and public health concern, creating a demand for sensitive, simple, and field-deployable detection methods. Gold nanoparticles capped with gallic acid (GA-AuNPs) offer a promising colorimetric platform because their optical properties change upon interaction with metal ions. However, reliable sensor performance requires not only analytical sensitivity but also a clear understanding of the underlying sensing mechanism. Integrating complementary analytical techniques is therefore essential to elucidate metal-ligand interactions, nanoparticle aggregation behavior, and signal generation, enabling rational sensor design and improved confidence in real-world environmental monitoring applications.

A one-pot synthesis of gallic acid-capped gold nanoparticles (GA-AuNPs) was developed, allowing Pb²⁺ to interact directly with the nanoparticles during formation and produce a distinct color change from red to purple to blue. Key analytical findings supporting the proposed sensing mechanism and its selectivity toward Pb²⁺. A detection limit of 0.62 μg L^-1 was achieved by UV-Vis spectroscopy, accompanied by clear spectral shifts, along with a distinct naked-eye color change that enables simple onsite screening. SP-ICP-MS revealed increases in particle size and decreases in particle number concentration, consistent with Pb²⁺-induced aggregation. FlFFF-ICP-MS showed co-elution of Pb and Au signals, confirming their associations. XPS identified O-Pb coordination, verifying that Pb²⁺ binds to the hydroxyl groups of gallic acid, and TEM provided direct visual evidence of nanoparticle aggregation.

Beyond a simple and cost-effective approach for Pb²⁺ detection, this study provides mechanistic insight into the GA-AuNP colorimetric response. Combined SP-ICP-MS, FlFFF-ICP-MS, XPS, and TEM analyses reveal a Pb²⁺-induced aggregation pathway driven by specific O-Pb coordination, advancing fundamental understanding of metal-ligand-nanoparticle interactions and supporting rational sensor design for environmental monitoring.