Modification-free colorimetric and visual detection of Hg2+ based on the etching from core-shell structural Au-Ag nanorods to nanorices

A simple and rapid colorimetric approach for Hg2+ detection is achieved by etching silver-coated gold nanobipyramids (Au NBs@Ag nanoparticles) based on the redox reaction between Hg2+ and silver nanoshell of the Au NBs@Ag nanoparticles. The decrease of the silver nanoshell thickness leads to first blue shift and then red shift of the longitudinal localized surface plasmon resonance (LSPR) peak and accompanies a vivid color change. The blue shift is more suitable for colorimetric detection which has the obvious multicolor change from yellow-green to green and then to blue-gray; and could be employed to quantitatively detect the concentrations of Hg2+. This nanoprobe with the longitudinal LSPR peak at 730 nm exhibits a linear range of 0.1-20 mu M with a limit of detection (LOD) of 22 nM based on blue shift and has the most obvious color change with the lowest LOD of 0.8 mu M by direct observation. In this case, the Au NBs@Ag nanoparticles are gradually etched from the nanorods to nanorices as the Hg2+ concentration increases. Compared with other techniques, this method could avoid tedious procedures and is time-saving. Furthermore, this nanoprobe has good selectivity, and is well demonstrated in real samples with satisfied results. (C) 2018 Elsevier B.V. All rights reserved.