A dual colorimetric probe for rapid environmental monitoring of Hg(2+) and As(3+) using gold nanoparticles functionalized with d-penicillamine

A highly sensitive and selective colorimetric assay for the dual detection of Hg(2+) and As(3+) using gold nanoparticles (AuNPs) conjugated with d-penicillamine (DPL) was developed. When Hg(2+) and As(3+) ions coordinate with AuNP-bound DPLs, the interparticle distance decreases, inducing aggregation; this results in a significant color change from wine red to dark midnight blue. The Hg4f and As3d signals in the X-ray photoelectron spectra of Hg(2+) (As(3+))-DPL-AuNPs presented binding energies indicative of Hg(2+)–N(O) and As(3+)–N(O) bonds, and the molecular fragment observed in time-of-flight secondary ion mass spectra confirmed that Hg(2+) and As(3+) coordinated with two oxygen and two nitrogen atoms in DPL. The detection of Hg(2+) and As(3+) can be accomplished by observing the color change with the naked eye or by photometric methods, and this was optimized to provide optimal probe sensitivity. The assay method can be applied for environmental monitoring by first selectively quantifying Hg(2+) in water samples at pH 6, then estimating the As(3+) concentration at pH 4.5. The efficiency of the DPL-AuNP probe was evaluated for the sequential quantification of Hg(2+) and As(3+) in tap, pond, waste, and river water samples, and absorbance ratios (A(730)/A(525)) were correlated with Hg(2+) and As(3+) concentrations in the linear range of 0–1.4 μM. The limits of detection in water samples were found to be 0.5 and 0.7 nM for Hg(2+) and As(3+), respectively. This novel probe can be utilized for the dual determination of Hg(2+) and As(3+), even in the presence of interfering substances in environmental samples.