Tracking Silver Nanoparticles during Their Synthesis by Inductively Coupled Plasma Mass Spectrometry: Implications for Colorimetric Sensing of Mercury Ions

Abstract

Silver nanoplates have been used in the colorimetric sensing of analytes through various mechanisms. Herein, we proposed the use of single-particle inductively coupled plasma mass spectrometry (SP-ICP-MS) for providing additional information on changes in nanoparticles during the colorimetric sensing of analytes. The information on equivalent spherical diameter and the number of particles obtained from SP-ICP-MS was employed for tracking the changes in silver nanoparticles during their synthesis process under various synthesis conditions and also during the colorimetric sensing of mercury. By comparing the edge size of triangular nanoplates observed by transmission electron microscopy, the information on the plate thickness of triangular silver nanoplates was also estimated by the size information from SP-ICP-MS. Four types of silver nanoplates were examined including bare silver nanoplates, silver nanoplates capped with glutathione, silver nanoplates capped with glutathione mixed with 0.05 mg L–1 mercury and bromide ions, and silver nanoplates capped with glutathione mixed with 1 mg L–1 mercury and bromide ions. The information on equivalent spherical diameter and the number of particles was used for understanding the sensing mechanism of the silver nanoplates toward mercury ions. The information from SP-ICP-MS was combinedly used with plasmon absorption data, as well as the information from field-flow fractionation-ICP-MS (FFF-ICP-MS), in order to study the changes in silver nanoparticles at various concentrations of mercury ions. A linear increase in particle concentrations was observed by SP-ICP-MS for the concentration range of 0.001–0.01 mg L–1 mercury ions. The particle concentrations were highest at 0.01 mg L–1 mercury ions and decreased to the same numbers as for the bare silver nanoplates without bromide etching. This study shows the potential use of SP-ICP-MS to provide additional information for tracking silver nanoparticles during their synthesis and colorimetric sensing of mercury ions. In addition, for SP-ICP-MS analysis of particle concentrations for the diluted silver nanoplates in contact with mercury ions before etching with diluted bromide ions, the limit of detection for mercury was pushed down to approximately 0.01 μg L–1, which would be very useful for the analysis of real samples under environmentally relevant conditions.