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Photoluminescent diamond nanoparticles as labels in cells: study of their optical properties and investigation of their cellular uptake mechanism, PhD Manuscript

PhD Manuscript, Orestis Faklaris

This thesis work studies the use of Photoluminescent NanoDiamonds (PNDs) for bio-imaging applications. Nanodiamonds are photoluminescent thanks to embedded nitrogen-vacancy (NV) color centers. The thesis is divided in two parts. The first part concerns the study of the optical properties of NV color centers in nanodiamonds. After optimization of the NV center concentration, we compared the photoluminescence of PNDs to commercial Quantum Dots (QDs) and conclude that it can be similar or even higher in the case of PNDs. To enhance the imaging contrast of internalized by cells PNDs, we studied the 2-photon excitation properties of NV centers. While implementing a pulsed excitation laser, we discovered that simultaneous one- and two-photon excitation (IR+VIS pulses) quenches the photoluminescence signal of PNDs. We examined how this effect can serve for super-resolution imaging of NV color centers in nanodiamonds. The second part of the work is devoted to the applications of PNDs as bio-imaging probes. In the prospect of applications of PNDs as drug delivery vehicles, we studied the uptake mechanisms of PNDs and elucidated their intracellular localization by blocking different entry mechanisms and by immunofluorescence experiments. Moreover, we ensured that PNDs are not toxic for cells in culture. As a first try of vectorization we covered PNDs with plasmid DNA and examined the transfection efficiency.

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