Nanoparticles such as Quantum Dots (QDs) have been widely used as fluorescence labels for sub-cellular imaging and as carriers for intracellular delivery of various biomolecules. QDs offer many advantages over traditional fluorescent labels such as high resistance to photo bleaching, small size, tunable emission spectra and have excitation spectra which allows for multiplexing. A major challenge with the use of QDs for cellular imaging and biomolecular delivery is the attainment of QDs freely dispersed inside the cells. Conventional methods such as endocytosis, lipids based delivery and electroporation are associated with delivery of QDs in vesicles and/or as aggregates that are not monodispersed. In this study, we demonstrate a new technique for reversible permeabilization of cells for the introduction of freely dispersed QDs within the cytoplasm. Our approach combines osmosis driven fluid transport into cells achieved by creating hypotonic environment and reversible permeabilization using low concentrations of cell permeabilization agents like Saponin. Osmosis driven fluid flow ensures unidirectional transport of QDs into the cell without loss of vital intracellular contents. Our results confirm that highly efficient endocytosis-free intracellular delivery of QDs can be accomplished using this method. The best results were obtained when the cells were treated with 50μg/ml Saponin in a hypotonic buffer at 3:2 physiological buffer: DI water ratio for 5 min at 4°C.
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