Current trends in atomic mass spectrometry for the speciation and imaging of metal-based nanomaterials

With the rapid development and growing number of applications of metal-based nanomaterials (metal-based NMs), it is of vital importance to evaluate their impact on both environmental and biological systems. The first step in assessing the impact is to determine exactly which metal-based NM species are where and in what quantities. Common approaches involve techniques like transmission electron microscopy (TEM) or scanning electron microscopy (SEM) for metal-based NM characterization and ICP-MS for total elemental analysis; however, these techniques cannot retrieve information pertaining to speciation, localization, or quantification of different metal-based NMs. This review summarizes approaches currently adopted for speciation and imaging of metal-based NMs, particularly in environmental systems. In response to the need to distinguish nanoparticles in the dissolved ionic fraction and/or distinguish them based on size, shape or coating for toxicity studies, more advanced methods and techniques are being developed. Various elemental imaging techniques are being used for the study of the localization of metal-based NMs within organisms as well as for speciation or quantification studies to evaluate the effects and influence of metal-based NMs on environmental and biological systems. It is envisioned that more complementary techniques (e.g. elemental and molecular techniques, mass spectroscopy and X-ray based techniques) will be employed to conduct quantitative analysis with imaging, speciation and elucidation, to better elucidate the fate and transformation of metal-based NMs. The results of these studies can provide valuable insights to understand the behavior and effect of metal-based NMs in different systems.