Thus, our strategy for the preparation of biocompatible quantum dots can evolve into the development of valuable luminescent probes with nanoscaled dimensions and optimal photophysical properties for a diversity of biomedical applications. Moreover, the internalized quantum dots are not cytotoxic and have essentially no influence on cell viability. Our hydrophilic nanoparticles can also cross the membrane of Chinese hamster ovarian cells and accumulate in the cytosol with limited nuclear localization. For example, boron dipyrromethene dyes can be connected to the hydrophilic quantum dots on the basis of amide bond formation to encourage the transfer of energy from the luminescent CdSe core to the organic dyes. Furthermore, the pendant carboxylic acids or primary amines of the macromolecular ligands can be exploited to modify the quantum dots after the adsorption of the polymers on their surface. In addition, these nanoparticles have relatively small hydrodynamic diameters (17-30 nm) and good quantum yields (0.3-0.4). Indeed, the coated quantum dots are readily soluble in water and are stable under these conditions for months over a broad pH range (4.0-12.0) and even in the presence of large salt concentrations. The CdSe core transforms from wurtzite to rock-salt structure near 6.3 GPa and then to Cmcm or distorted Cmcm structure probably occurs at 45.1 GPa which has not been. The narrow photoluminescence (fwhm 40 nm) from these composite dots spans most of the visible spectrum from blue through red with quantum yields of 3050 at room temperature. The structural phase transition of CdSe/ZnS core/shell quantum dots (QDs) has been studied by in situ angle-dispersive X-ray diffraction under high pressure up to 53.6 GPa. The thiol groups encourage the adsorption of these macromolecular constructs on the ZnS shell of the nanoparticles, and the poly(ethylene glycol) chains impose hydrophilic character on the resulting assemblies. We report a synthesis of highly luminescent (CdSe)ZnS composite quantum dots with CdSe cores ranging in diameter from 23 to 55 A. We synthesized macromolecular ligands for CdSe-ZnS core-shell quantum dots incorporating multiple thiol groups, poly(ethylene glycol) chains, and either carboxylic acids or primary amines along a common poly(methacrylate) backbone.
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