Résumé
Fluorescent nano-diamonds (fND) are attractive tools for nanoscale biological cellular imaging allowing both photoluminescence and magnetic resonance imaging [1]. Recent technological developments enable to fabricate bright fND particles of various sizes with high content of nitrogen-vacancy (NV) centres [2]. In this work we study internalization processes of NDs in the breast cancer MCF7 1DIV cell line using Atomic Force Microscopy imaging and force spectroscopy. fND particles of size range from 5 to 60 nm were used, prepared from Ib synthetic diamond, electron irradiated, annealed and plasma oxidized to create NV centers.Changes of cells stiffness were detected by AFM force measurements after introducing the fNDs into the cell medium. We observed an oscillating variation of cell membrane Young's modulus while the cells become stiffer. We believe that repetitive uptake/release processes of fNDs are responsible for these mechanical changes. Contrarywise, more confluent MCF7 cells (3DIV) did not show any significant change in Young’s Modulus, as compare with control ones. Indeed, it has been shown that differences in nanoparticle uptake can arise from how close the cells are to one another (confluence) [3] and how old they are.Moreover, our results suggest that studies on fNDs uptake should consider the cell cycle, as in a cell population, the dose of internalized nanoparticles in each cell varies as the expression of membrane proteins vary during the cell cycle [4]. The cell cycle is a series of events that lead to cell division and replication, consisting of four phases: G1 (when the cell increases its size), S (the cell synthesizes DNA), G2 (the cell synthesizes proteins for cell division) and M (the cell divides and the two daughter cells enter the G1 phase). During each event, cellular processes can vary; meaning that the rate at which a cell takes up foreign material, as for instance nanoparticles, may depend on the phase the cell is in [4-6], modifying accordingly their elasticity. When nanoparticle internalization is studied, it is therefore crucial to resolve how the state of the different cells affects the uptake. [1] L. Moore, M. Nesladek et al., Nanoscale (2014).[2] J. Havlik, M. Gulka, M. Nesladek et al., Nanoscale (2013).[3] B. Snijder, et al. Nature 461, 520–523 (2009). [4] E. Boucrot and T. Kirchhausen, Proc. Natl Acad. Sci. USA 104, 7939–7944 (2007). [5] D. Raucher and M. P. Sheetz, J. Cell Biol. 144, 497–506 (1999).
[6] J. K. Schweitzer, E. E. Burke, H. V Goodson and C. D’Souza-Schorey. J. Biol. Chem. 280, 41628–41635 (2005).