Graphene, a single layer of hexagonally arranged carbon atoms, is considered the most versatile material available to mankind: the thinnest, the strongest, the lightest, extremely flexible, highly electrically and thermally conductive material, [1,2] a versatile entity for multiple functionalization. Due to its unique combination of superior properties, graphene is the starting platform for new disruptive technologies across a wide range of fields [3,4] Various graphene-based technologies have now transformed into commercial products, in sports goods, automotive coatings, conductive inks, touch screens and several others. [5] The massive production and use of graphene materials will increase exponentially over the coming years. On the other hand, an ever-growing literature is related to the explorations of graphene materials for new diagnostic and therapeutic strategies. [6][7][8][9] The graphene material exposure, due to the different applications, might open possible threats Considering the potential exposure to graphene, the most investigated nanomaterial, the assessment of the impact on human health has become an urgent need. The deep understanding of nanomaterial safety is today possible by high-throughput single-cell technologies. Single-cell mass cytometry (cytometry by time-of flight, CyTOF) shows an unparalleled ability to phenotypically and functionally profile complex cellular systems, in particular related to the immune system, as recently also proved for graphene impact. The next challenge is to track the graphene distribution at the single-cell level. Therefore, graphene oxide (GO) is functionalized with AgInS 2 nanocrystals (GO-In), allowing to trace GO immune-cell interactions via the indium ( 115 In) channel. Indium is specifically chosen to avoid overlaps with the commercial panels (>30 immune markers). As a proof of concept, the GO-In CyTOF tracking is performed at the single-cell level on blood immune subpopulations, showing the GO interaction with monocytes and B cells, therefore guiding future immune studies. The proposed approach can be applied not only to the immune safety assessment of the multitude of graphene physical and chemical parameters, but also for graphene applications in neuroscience. Moreover, this approach can be translated to other 2D emerging materials and will likely advance the understanding of their toxicology.
