Observing zinc oxide nanoparticles suspension stability in various media by using single particle inductively coupled plasma mass spectrometry (SP-ICP-MS)

Zinc oxide (ZnO) nanoparticles are widely used in industry due to their ability to absorb UV light and antibacterial property. The total surface area of ZnO nanoparticles affects its properties and applications. Therefore, the size and stability control of ZnO nanoparticles is very important. We explored the ability of single particle inductively coupled plasma mass spectrometry (SP-ICP-MS) in combination with settling process to analyze ZnO nanoparticles suspended in various media, by which the method allows to detect specific nanoparticles at very low concentration. The settling experiment of ZnO nanoparticles suspended in various media, including deionized water, non-ionic, cationic and anionic surfactants, was carried out to study size, stability and dispersion. The SP-ICP-MS along with settling experiment was set up by suspending different sizes of ZnO nanoparticles in deionized water, Triton X-100, cetyltrimethylammonium bromide and sodium dodecyl sulfate, followed by collecting the sample at various times and vertical distances. Then, the collected samples were diluted and analyzed by SP-ICP-MS to obtain the information on particle size distribution and the particle number concentration. The size and morphology of the ZnO nanoparticles were observed by transmission electron microscopy technique and zeta potential values of particles suspension were measured. The total concentrations of Zn in the suspension were also analyzed by conventional mode ICP-MS to compare with single particle mode ICP-MS. The information obtained in this work allows us to assess the stability of ZnO nanoparticles in various media and shows that the newly developed approach based on SP-ICP-MS with settling experiment can be used as an alternative characterization tool to evaluate the stability of nanoparticles.