METALLIC NANOPARTICLES CHARACTERIZATION BY INDUCTIVELY COUPLED PLASMA MASS SPECTROMETRY

In the context of surface-enhanced Raman spectroscopy analysis, metallic nanostructures are used to improve the sensitivity of the Raman scattering. These nanostructures, called SERS substrates, are generally nanoparticles (Nps) made of gold (AuNps) or silver (AgNps). Most of the time, each lab synthesizes its own SERS substrates. However, given that Nps properties directly influence the signal exaltation, different characterization techniques are used to determine their size or shape such as dynamic light scattering (DLS), UV-Visible spectroscopy, electronic microscopy, …
This study presents an innovative technique based on the inductively coupled plasma mass spectrometry coupled with a single particle module (spICP-MS) to determine, in a single analysis, information about the size, size distribution, Nps concentration and residual metallic salts concentration. In this framework, the sample is diluted to get one particle at the same time in the plasma prior its decomposition in an ion cloud. The signal intensity is related to the Nps size while the frequency is linked to the Nps concentration. This study compared 3 suspensions of AgNps and AuNps synthesized according to the widely used Lee-Meisel process [1]. Three replicates were prepared for each synthesis. It appeared that AuNps mean size was equal to 25 nm ± 1 nm (n=3) with relative standard deviation (RSD) between replicates comprised below 6 %. For silver, Nps mean size was 57 nm ± 9 nm (n=3) with a RSD from 2 to 7 % between replicates. Syntheses were also analyzed by DLS to compare the measured sizes. The mean size for AuNps varies by 1 nm between the two techniques while 6 nm differentiate the mean size for AgNps. Concerning the Nps concentration, similar results were obtained for each replicate and are in the order of 7.7 x107 particles/L for gold and 1.2 x108 particles/L for silver. In conclusion, spICP-MS appeared as a promising tool to rapidly and accurately characterize SERS substrates in terms of size, size distribution but also for the concentration of nanoparticles.