Separation and characterization of gold nanomaterials with different shapes using AF4-ICP-MS and single-particle ICP-MS

The toxicity profiles of nanomaterials (NMs) are affected by their chemical composition, size, and shape. Inductively coupled plasma mass spectrometry (ICP-MS) is a robust, element-specific analytical tool for detecting the chemical composition of NMs. Fast time-resolved analysis by single-particle ICP-MS (spICP-MS) enables the discrimination of individual nanoparticles and the determination of their sizes based on elemental content. However, because spICP-MS evaluates particle sizes on the basis of their elemental mass, it cannot distinguish differently shaped NMs with identical volume. In this study, we used asymmetric flow field-flow fractionation coupled with ICP-MS (AF4-ICP-MS) to separate gold NMs of different shapes. Although clear separation was not achieved with AF4-ICP-MS, the signal intensities of NMs with similar volumes but different shapes varied significantly in spICP-MS analysis; namely, nanorods and nanoplates exhibited lower signal intensities than nanospheres with similar volumes. These results suggest that the ionization efficiency of NMs in the ICP is influenced by particle shape, with incomplete ionization preferentially occurring in nanorods and nanoplates. Our findings demonstrate the potential of spICP-MS for shape-dependent separation and characterization of NMs.