A single-step low cost detection of ground water Hg < sup > 2+ < /sup > using mercaptosuccinic acid functionalised silver nanoprism

Abstract

We are reporting a rapid, highly sensitive, specific and cost-effective detection platform for Mercuric Ion (Hg2+) present in ground water using the dipole sensitive spectroscopic properties of Silver nanoprism (AgNPR). We synthesised AgNPR incorporating Bovine serum albumin (BSA) within its interstitial crystal planes to enhance solution stability and shelf-life. AgNPR was functionalised with mercaptosuccinic acid for Hg2+ specific interactions. The Dipole resonance peak (D-peak) of AgNPR exhibited 30 nm shift towards shorter wavelength in the presence of 1 µM Hg2+, accompanied with a change in colour from blue to purple. The interaction was highly specific for Hg2+ with a limit of detection (LOD) of 8.13 nM (1.62 ppb) that is much within United States Environment Protection Agency (EPA) and World Health Organization (WHO) recommended range. Transmission electron microscopy (TEM) demonstrated, at lower concentrations of Hg2+ (≤0.1 µM), the spectral changes are consistent with Hg2+ induced displacement of (Mercaptopropyl Succinic Acid) MSA from AgNPR surface and subsequent etching of AgNPR vertices by Cl- ions. Fringe length analysis performed on the high resolution TEM images of AgNPR indicated formation of Ag-Hg amalgam at higher concentrations of HgCl2 (1.0 µM). X-Ray diffraction (XRD) study also supported the mechanism. Density Functional Theory (DFT) calculations substanciated the selective interaction between MSA-AgNPR and Hg2+. We have tested real water sample spiked with Hg2+ by our method and found excellent recovery result comparable with the gold standard of ICP-MS measurement.