Single molecule observation is of great importance in life sciences. Individual probing enables studies of biomolecules interactions directly. 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 [1] represent a promising alternative to inorganic biomarkers. Indeed NV color centers neither photobleach nor blink and are biocompatible [2][3][4]. Here we demonstrate the efficient uptake of PNDs of size smaller than 50nm 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.
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