Polyvalent Nanoparticle-DNA Conjugates: Synthesis, Properties, and Biodiagnostic ApplicationsPublic Deposited
The work of this dissertation was aimed at synthesizing new types of nanoparticle-DNA conjugates, investigating their chemical and physical properties, and exploring their biodiagnostic applications. Chapters Two and Three describe the synthesis of new types of nanoparticle-DNA conjugates: (1) silver nanoparticle-DNA conjugates (DNA-Ag NPs) and (2) 2-nm gold nanoparticle-DNA conjugates (DNA-Au NPs). These DNA-Ag NPs have optical properties that are distinct from the gold analogues and open up possibilities for multiplexing and the development of labels for surface-enhanced Raman spectroscopy-based detection systems. In chapter Three, a novel method for isolating 2-nm DNA-Au NPs from free excess DNA is described. These small particles typically require cumbersome electrophoretic methods to isolate them, but their cooperative binding properties can be used to selectively address them in the presence of free DNA of the same sequence. Chapter Four presents a study aimed at characterizing the particle size-dependent melting properties of DNA-Au NP aggregates. Significantly, it was discovered that subtle differences in melting transitions (Tms) for particles that vary in size can be utilized for the size-selective separation of Au NP mixtures. Specifically, the Tms of DNA-Au NP aggregates are shown to be proportional to particle size. It is shown that binary and ternary mixtures of gold nanoparticles can be size-selectively separated based upon this principle. The remainder of this dissertation describes several novel biodiagnostic applications of DNA-Au NPs. Two multiplexed assays have been developed for the detection of three proteins and four oligonucleotides, respectively. In addition, two new methods for detecting Hg2+ have been developed. One is a colorimetric assay that takes advantage of the plasmonic properties of gold nanoparticle probes, while the other is a chip-based assay that takes advantage of the catalytic properties of gold nanoparticle probes to provide signal amplification. In both assays, recognition of Hg2+ is accomplished through the use of probes with duplex sequences that have T-T mismatches. Such mismatches are extremely selective for Hg2+. Finally, a competition-based assay has been developed for cysteine that relies on the ability of cysteine to complex Hg2+ at a T-T mismatch and lower the Tm for the duplex structure.