A Highly Sensitive and Selective Colorimetric Hg²⁺ Ion Probe Using Gold Nanoparticles Functionalized with...

A highly sensitive and selective colorimetric assay for the detection of Hg²⁺ ions was developed using gold nanoparticles (AuNPs) conjugated with polyethyleneimine (PEI). The Hg²⁺ ion coordinates with PEI, decreasing the interparticle distance and inducing aggregation. Time-of-flight secondary ion mass spectrometry showed that the Hg²⁺ ion was bound to the nitrogen atoms of the PEI in a bidentate manner (N-Hg²⁺-N), which resulted in a significant color change from light red to violet due to aggregation. Using this PEI-AuNP probe, determination of Hg²⁺ ion can be achieved by the naked eye and spectrophotometric methods. Pronounced color change of the PEI-AuNPs in the presence of Hg²⁺ was optimized at pH 7.0, 50°C, and 300 mM·NaCl concentration. The absorption intensity ratio (A₇₀₀/A₅₁₄) was correlated with the Hg²⁺ concentration in the linear range of 0.003-5.0 μM. The limits of detection were measured to be 1.72, 1.80, 2.00, and 1.95 nM for tap water, pond water, tuna fish, and bovine serum, respectively. Owing to its facile and sensitive nature, this assay method for Hg²⁺ ions can be applied to the analysis of water and biological samples.