<i>In situ</i> preparation of Ag nanoparticles by laser photoreduction as SERS substrate for determination of Hg²⁺

Abstract

This paper reports a new way to fast produce surface‐enhanced Raman scattering (SERS) substrate within 1 s by in situ photoreduction of AgNO 3 and chemical compound containing mercapto group, such as para‐aminothiophenol (PATP), dithizone, and 4‐mercaptobenzoic acid on filter paper. Ag nanoparticles (Ag‐NPs) would form in the area where the laser spot was focused by Raman instrument. In this work, the preparation of Ag‐NPs and excitation of SERS signal could be achieved simultaneously within 1 s. However, no SERS signal and Ag‐NPs were observed when rhodamine 6G and crystal violet were employed in place of the aforementioned molecules after the same operation. About 0.5 μM PATP, 5 μM dithizone, and 1 μM 4‐mercaptobenzoic acid could be fast detected by this method. According to this phenomenon, a fast and sensitive way to detect Hg 2+ based on a competitive reaction among PATP, Ag + , and Hg 2+ was developed. With the addition of Hg 2+ , PATP was removed from Ag + owing to the stronger interaction between –SH and Hg 2+ . This behavior inhibited the formation of Ag‐NPs, leading to a decrease of the intensity of the SERS signal. The decrease of SERS intensity was used to determine the concentration of Hg 2+ . Under optimal conditions, this method can be utilized to detect Hg 2+ at a detectable level of a concentration of 4 nM in aqueous solution. Additionally, the Raman mapping experiment demonstrated good point‐to‐point repeatability with a relative standard deviation of less than 7%. Therefore, this sensing platform is a promising candidate for fast and real‐time mercuric ion detection. Copyright © 2016 John Wiley &amp; Sons, Ltd.