Synthesis, functionalization, and biological tagging applications of II-VI semiconductor nanocrystals

Fluorescent labeling of biological molecules is a technique that is used widely for analytical purposes in biotechnology and bioengineering. It typically involves the use of an organic dye molecule linked to a moiety that selectively bonds a particular biological molecule, allowing the detection of the latter by the fluorescence of the dye molecule. Semiconductor nanocrystals or quantum dots have emerged as a new class of fluorescent markers with distinct advantages over the traditional organic dyes. Their attractive properties include narrow, symmetric, and bright emission, continuous excitation by any wavelength smaller than the emission wavelength, broad absorption spectrum, long lifetime, resistance to photobleaching, as well as excellent optical and chemical stability that allows their use in lengthy experiments.; The focus of this thesis is the synthesis and surface functionalization of ZnSe quantum dots and (ZnSe)ZnS core-shell nanostructures, and their biological conjugation with DNA and protein.; The ability to synthesize different populations of quantum dots with narrow emission spectra permits multiplexing, a property that is very important for simultaneous detection of several analytes, which would be very tedious and expensive if done sequentially. Highly luminescent ZnSe nanocrystals have been synthesized using a hot-injection colloidal method. The synthesis was performed in a stirred batch reactor containing liquid hexadecylamine at 310°C. The precursors were diethylzinc diluted in heptane and selenium powder mixed with trioctylphosphine. The mixture of reactants was injected into the batch reactor and the time of reaction was used to control the size and luminescence emission wavelength of the quantum dots. In order to optimize the process various parameters that can influence the photoluminescence property of quantum dots obtained were investigated, such as surfactant addition, temperature, precursor ratio, and mixing conditions.; Capping of the ZnSe quantum dots with a ZnS layer to obtain a core-shell nanostructure improves the nanocrystal surface passivation. As a result, the fluorescence emission intensity or quantum yield of quantum dots is enhanced without significantly affecting the emission wavelength.; Surface ligand exchange reactions with mercapto-alcohols and mercapto-acids and surface modification with surfactants and polymers were investigated to identify the best approach for obtaining water-soluble ZnSe and (ZnSe)/ZnS quantum dots that are stable in an aqueous solution and suitable for biological applications. (Abstract shortened by UMI.)...