Ultrasensitive detection and co-stability of mercury(ii) ions based on amalgam formation with Tween 20-stabilized silver nanoparticles

Abstract

A rapid and sensitive colorimetric sensing strategy employing silver nanoparticles (AgNPs) to detect trace Hg²⁺ in aqueous solutions is described. The citrate-capped AgNPs were functionalized to form a Tween 20-stabilized AgNPs (Tween 20-AgNPs) probe, which was stable in a high ionic strength environment. When Hg²⁺ was present in the aqueous solution, citrate reduced Hg²⁺ to Hg⁰ and formed a Ag/Hg amalgam with the AgNPs, followed by the removal of Tween 20 from the surface of the AgNPs. The AgNPs were unstable in high ionic strength solutions, resulting in AgNPs aggregation and co-stabilization with Hg²⁺, observed by a decrease in the UV-vis absorption. This decrease in the UV-vis absorption was proportional to the concentration of Hg²⁺. Under optimized conditions, the sensing system exhibited a linear range of 5.0 × 10⁻¹⁰ to 1.2 × 10⁻⁷ M for Hg²⁺, with a detection limit of 0.31 nM in buffer. The co-stabilization assays showed no Hg²⁺ was detected to be remaining in solution using our proposed method. The AgNPs removal percentage was correlated well with the concentration of Hg²⁺ with a correlation coefficient of 0.99862. When the concentration of Hg²⁺ was in excess, the AgNPs removal percentage correlated with the concentration of AgNPs with a correlation coefficient 0.994 as well. Moreover, this probe was successfully used to detect and co-stabilize Hg²⁺ in tap water, spring water, and surface water samples.