Use of field-flow fractionation and single particle inductively coupled plasma mass spectrometry for the study of silver nanoparticle shape transformation

Field-flow fractionation-inductively coupled plasma mass spectrometry (FFF-ICP-MS) and single particle ICP-MS (SP-ICP-MS) were used for investigation of silver nanoparticle shape transformation. Commercial and laboratory synthesized silver nanoparticles were employed in this study. For laboratory synthesized silver nanoparticles, silver nanosphere seed was first prepared by reducing silver nitrate with sodium borohydride in starch stabilizing agent. The obtained nanosphere exhibited 27.5 nm hydrodynamic diameter from FFF-ICP-MS analysis with equivalent spherical diameter of 26 nm from SP-ICP-MS analysis. This nanosphere underwent shape trans-formation induced by varying volumes of hydrogen peroxide. Increasing hydrogen peroxide volume resulted in increased particle diameter, and nanoplate formation. These synthesized nanoparticles and commercial silver nanoplates were subjected to shape transformation induced by bromide etching. General trend was observed that bromide addition caused particles to become smaller. Clear trend was found for commercial silver nanoplates that bromide addition caused both hydrodynamic diameter measured by FFF-ICP-MS and equivalent spherical diameter measured by SP-ICP-MS become smaller. Furthermore, the combined information from FFF-ICP-MS and SP-ICP-MS analysis with the use of TEM data were proposed to provide additional information on the edge length and the thickness of silver nanoplates. With the known edge length of commercial silver nanoplates, the thickness was estimated to be 25.4 nm, 7.64 nm, and 4.95 nm for triangular nanoplates with the edge length of 32 nm, 70 nm, and 153.1 nm, respectively. Both FFF-ICP-MS and SP-ICP-MS provided unique information which are useful for nanoparticle characterization.