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Quantum dots (QDs) are a diverse class of engineered nanomaterials that have great potential for use as agents in imaging, diagnostics and drug-delivery because of their intense and photostable fluorescence. Advances in the field of nanotoxicology, however, have recently identified potential risks and hazards associated with exposure to QDs. The main purpose of this research is to investigate the capabilities of a synergistic range of different techniques, including cytotoxicity assays, confocal microscopy and vibrational spectroscopy, to probe their interaction with Biological systems. With the combination of these techniques it is hoped to understand the mechanisms of the interaction of QDs with biological systems. Cytotoxicity assays demonstrate that polyethylene glycol (PEG) coated CdSe/ZnS quantum dots are at most weakly cytotoxic upon prolonged exposure. Simultaneous exposure to simulated solar illumination indicates an increased cytotoxic response and potential risks of phototoxicity. Fluorescence and Confocal Microscopy studies demonstrate that the internalization of QDs within HaCaT keratinocytes occurs within 1 hour of exposure, and that QDs are retained in the lysosomes supporting a model of nternalisation by endocytosis. Using an excitation wavelength of 785 nm, the two-photon excitation fluorescence of QDs (emission at 625 nm) is observed, whereby the fluorescent emission is observed in the anti-Stokes Raman signal, together with the usual Stokes Raman scatter of a single cell. Raman microspectroscopy therefore offers the means to both localise (image) and study the chemical interaction between a nanoparticle and its biological environment as well as the overall changes to the physiology of the cell as a result of interaction with the nanoparticles. Localisation of QDs is possible due to the high fluorescence of these nanomaterials. In the last chapter a novel technique is investigated for detection of non fluorescent nanomaterials within a cell. The characteristic Raman signature of the nanoparticles is extracted from the mixed nanoparticle/cellular spectrum using a cross correlation technique, and the signature is colocalised with the fluorescent signal in the case of QDs. The technique is validated using simulations and experimental data.
Salford, Lorenzo: Spectroscopic Imaging of Quantum Dot Cellular Interactions. M. Phil Thesis. Dublin Institute of Technology, 2009.