Nucleic acids-templated semiconductor nanocrystals: Synthesis and bioimaging applications.

摘要

Semiconductor nanocrystals are used widely as biological labels and components of optoelectronic devices. The spectral tunability and stability of these materials makes them ideal building blocks and probes. This thesis describes work on a class of semiconductor nanocrystals with properties controlled by the structure and sequence of nucleic acids. Controlling nanocrystal properties using rationally designed nucleic acids structures and sequences presents a new means to engineer inorganic structures with desired properties, and provides a means to produce biofunctionalized imaging labels in a single step. The materials produced using this approach have favorable characteristics, including bright emission, high stability, and straightforward synthetic manipulation.;DNA-passivated semiconductor nanocrystals exhibit low cytotoxicity and high stability in biological media and thus are superior for bioimaging applications. Given the molecular recognition properties of DNA and RNA aptamers with other biomolecules such as proteins or cell surface receptors, we were inspired to use a bi-functional DNA template to generate biofunctionalized semiconductor nanocrystals in a simple one-pot process. This novel strategy is realized by the design of a chimeric DNA template with a phosphorothioate domain for semiconductor nanocrystals passivation and a phosphate domain (aptamer) for biomolecule recognition. CdTe semiconductor nanocrystals synthesized with the chimeric DNA template possess high specificities towards the cognate DNA, protein, and cancer cell targets.;The properties of semiconductor nanocrystals are known to be strongly dependent on the ligand used during synthesis that serves to passivate the surface. We endeavored to use a class of ligands that would have intrinsic self-assembly properties and inherent biocompatibility. We therefore tested nucleic acids including DNA and RNA molecules as ligands for cadmium and lead-based nanocrystals formation. Nucleic acids molecules passivate on semiconductor nanocrystal surface through their nucleobase functionalities as well as the phosphate backbone. Among the four natural mononucleotides, guanine is the most effective nucleotide for semiconductor nanocrystals formation. Semiconductor nanocrystals synthesized with different DNA homopolymer sequences possess distinct luminescence intensities. A general approach is being developed to systematically control semiconductor nanocrystals luminescence using rationally designed DNA sequences. In addition, the effect of nucleic acids structure on CdS semiconductor nanocrystals properties is elucidated using transfer RNA molecules as a ligand system, and differences in size and morphology were observed for the semiconductor nanocrystals synthesized with different RNA structures.