Colorimetric detection of lead(ii) ions based on accelerating surface etching of gold nanorods to nanospheres: the effect of sodium thiosulfate

Abstract

A non-aggregation colorimetric sensing method based on the accelerated etching of gold nanorods (AuNRs) has been developed for detecting lead(II) ions (Pb²⁺). In this method, the addition of Pb²⁺ leads to the formation of a monolayer of AuPb₂ and AuPb₃ alloys on the gold surface, which results in a considerable decrease in the surface electrode potential. Therefore, the sodium thiosulfate induced dissolution rate of AuNRs has been accelerated. Because of this accelerated etching, the shape of the AuNRs changes rapidly to gold nanospheres. This morphology transformation leads to a blue shift and fade down of the longitudinal localized surface plasmon resonance (LSPR) absorption band of AuNRs until it merges into the transversal absorption. The qualitative spectral change from double bands to single band LSPR results in a distinct irreversible color change in the gold colloid from blue to red. This colorimetric sensing method can be used to detect Pb²⁺ with excellent selectivity and high sensitivity. Under the optimized conditions, the lowest limit of detection for Pb²⁺ observed by the naked eye is 0.1 μM and 20 nM measured by UV-Vis spectroscopy. In the concentration range from 25 to 300 nM of Pb²⁺, this sensing method exhibits a good linear relationship. This colorimetric sensing method for Pb²⁺ has promising applications in water and human serum analysis.