Highly selective colorimetric sensing for iodide in water based on a novel surface passivation of Ag nanoprisms

Abstract

Because silver (Ag) nanoprisms with sharp edges are inherently unstable, it is very important to develop a facile method that can dramatically improve the chemical stability of Ag nanoprisms while maintaining their inherent properties, including their plasmonic properties. In the present work, we developed a novel surface passivation method based on a single-step water-based process and showed that it significantly improved the chemical stability of Ag nanoprisms. Specifically, tetramethylethylenediamine (TMEDA) was used as an organic capping ligand, and the TMEDA-treated Ag nanoprisms retained their triangular shape even when exposed to various strong etchants including bromide, chloride, and hydrogen peroxide. Only in the presence of iodide did the sharp corners of the nanoprisms become spontaneously etched, and this etching resulted in a dramatic change in their localized surface plasmon resonance (LSPR) properties. The extent of the change of the LSPR properties depended on the concentration of iodide; hence, aqueous solutions of the TMEDA-treated Ag nanoprisms with different concentrations of iodide showed different colors. Based on this relationship, a colorimetric sensing probe that can detect iodide in aqueous solutions was developed. The sensing probe exhibited very high selectivity for iodide and the ability to determine the concentration of iodide over a wide range of concentrations. In addition, the probe was found to provide significant advantages over previously developed systems for iodide analysis, including portability, ease of use, point-of-care analysis, and naked-eye detection.