Diamond photoluminescent nanoparticles as innovative markers to study intracellular processes

In order to achieve an efficient biolabeling, a reliable marker is needed. Organic dyes and fluorophores are widely used, but they lack of photophysical stability. Alternative systems are Quantum dots (QDs). Although very efficient for multicolour staining and no photobleaching, they suffer of photoblinking and may be cytotoxic in long term. In contrast, diamond nanoparticles (NDs) containing nitrogen- vacancy (NV) color centers represent a promising alternative to inorganic biomarkers. Here we demonstrate the efficient uptake of PNDs of size smaller than 50 nm at the single particle level in cultured cells. We improve cell imaging, examine for the first time thoroughly their internalization pathway, study the influence of their size, shape and surface groups to their internalization and compare their photoluminescence with that of QDs. Creation and stabilization of NV color centers is performed by high energy proton irradiation and subsequent annealing. After incubation with NDs, cells were fixed and mounted on microscope slides. For immunofluorescence analysis the endosomes and lysosomes were stained. The photoluminescence properties of individual nanoparticles in cells were studied either by a commercial confocal microscope. Cells were also treated with antibiotics which block endocytosis or block different endocytotic pathways and NDs internalization was examined.