Semiconductor nanocrystals, nanorods, nanowires and applications in biomolecular integration

Inorganic nanostructures interfaced with biological molecules have recently generated much interest in biology, oncology, and medical fields. Semiconductor II-VI nanocrystals have found much use in biological applications for fluorescence cell imaging, tracking, and sorting. Due to quantum confinement effects, nanocrystal size and shape alters optical and electrical properties. A general method of shape control for cadmium chalcogenide nanocrystals, specifically CdSe, CdS, CdTe, was developed and extended to the synthesis of mixed-semiconductor heterostructures. Cadmium chalcogenide nanocrystals were synthesized by thermal decomposition of organometallic precursors. A single injection of chalcogenide precursor resulted in farily monodisperse spherical nanoparticles; whereas multiple injections resulted in nanorods elongated along their c-axis. Nanoparticles and nanorods were primarily wurzite in structure, but spherical nanoparticles exhibited a greater amount of stacking faults. The shape evolution of nanocrystals was indicated by a red shift in emission spectra and decrease in photoluminescence intensity. Injection of a different chalcogenide precursor yielded both types I and II linear heterostructures. Thus the shape of anisotropic nanocrystals may be kinetically controlled by rate of chalcogenide injection. Due to their near-infrared emission, CdTe nanocrystals were chosen as fluorescent markers for prostate carcinoma cell labeling purposes. Shape and size monodisperse CdTe nanocrystals were rendered water-soluble and biocompatible prior to conjugation with prostate-specific membrane antigen (PSMA) aptamers. CdTe-aptamer, and ZnS/CdSe-aptamer bioconjugates specifically labeled both live and fixed cells and overexpressing PSMA in vitro. In preparation for in vivo studies, CdTe-PSMA bioconjugates were tested for long term luminescence and photostability in biological environment as well as depth of penetration for specific labeling of tissue phantoms. Biomolecules may also be integrated with non-colloidal nanocrystals. Peptides selective for germanium nanowires and wafers were isolated using phage display. Peptides expressed on the minor protein coat of bacteriophage were incubated with germanium substrates to find the sequences with greatest affinity for its substrate. Binding affinities were quantified by fitting titer measurements to an adsorption isotherm. Peptides selected using phage display was found to be morphologically selective for germanium substrates. Much research has yet to be conducted with the integration of inorganic with biomaterials, as the potential applications of these integrated materials continues to expand.