Synthesis, Purification, Characterization and Application of Discretely Functionalized Gold Nanopartides

In this thesis, it describes the synthesis, purification, characterization and applications of mono-amine functionalized gold nanoparticles (AuNPs) with an average diameter of 2 nm. Mono-amine functionalized AuNPs were synthesized by employing the ON/OFF switchable recognition between ammonium salt and dibenzo[24]crown-8 in acid/base condition together with the site isolation effect based on a solid phase supported polystyrene Wang resin. The crude mono-amine functionalized AuNPs were purified by magnetic separation using dibenzo[24]crown-8-coated superparamagnetic iron oxide nanoparticles via pH-switchable pseudorotaxane formation. The purified product as well as the intermediates during synthesis was characterized by infrared (IR) and X-ray photoelectron spectroscopies (XPS). The mono-amine functionality of the AuNPs was characterized by the formation of the novel supramolecular dimers and trimers, titrating with bis-dibenzo[24]crown-8 and tris-dibenzo[24]crown-8. Furthermore, transmission electron microscopy (TEM) images show that there were significant amounts of AuNP supramolecular dimers in the solutions and that there were both AuNP dimers and trimers in the supramolecular trimer solutions. The trimers observed under the TEM were triangular or near-linear shapes. Moreover, UV/visible spectroscopic analysis of the supramolecular AuNP dimer and trimer solutions in different ratios between the crown ether linker and AuNPs demonstrated a gradual appearance of the two distinct plasmonic resonance bands at 620 and ∼700 nm.;The discretely mono-amine functionalized AuNPs could be simultaneously purified and detected by a real-time surface plasmon resonance (SPR) with organic solvent-compatible micro fluidic device/instrumentation. The discretely functionalized AuNPs could be assembled and disassembled on the surface of dibenzo[24]crown-8 coated gold plate via pH-switchable pseudorotaxane formation and dethreading in the microfluidic device. The monovalent attachment and detachment of AuNPs on gold surface gave real-time plasmonic signals which were successfully monitored by SPR. Furthermore, the self-assembly and disassembly processes of crude AuNPs and randomly functionalized gold nanoparticles were also monitored by SPR. The SPR results revealed that the crude and randomly functionalized AuNPs possessed different self-assembling and disassembling properties so that the mono-amine discretely functionalized AuNPs could be purified and simultaneously obtained with a SPR real time signal. The randomly functionalized AuNPs possessed incomplete disassembly during the pH-switching processes. Such observations together with the complete pH-switching of mono-functionalized AuNPs on gold surface were also characterized by atomic force microscopy (AFM).;The discretely functionalized AuNPs were further explored as a probe for DNA sensing. Mercapto-oligonucleotides were immobilized to the mono-amine AuNPs through thiol-maleimide click reactions with a hetero-bifunctional linker. Two types of primer (5 base pairs) were functionalized onto the AuNPs. These DNA-AuNPs hybridized complementarily with the sequence of the pathogenicity island of vancomycin-resistant Enterococcus faecalis so as to detect its presence. The DNA-AuNP detection was operated in organic solvents- N,N'- dimethylformamide (DMF), chloroform, and trace amount of water with sodium chloride and characterized by UV/visible absorption spectroscopy. UV/visible absorption of the system at 521 nm was monitored for the DNA hybridization. The melting temperature (Tm) studies were performed with different solvent system ratios, different alignments (tail-to-tail and head-to head) of AuNPs and different amounts of sodium chloride. The Tm was found to be higher with increasing salt concentrations and increasing ratios of chloroform to DMF. Moreover, the Tm was found to be similar with different alignments (tail-to-tail and head-to-head ) of AuNPs which were different from the randomly functionalized gold nanoparticles that reported previously in the literature.