Browsing by Author "Zhang, Aobo"

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    Surface Chemistry of Gold Nanoparticles and Applications
    (2022-06-24) Zhang, Aobo; Hafner, Jason H
    The interactions between commonly used surfactants and gold nanoparticles (GNPs) are studied primarily by surface enhanced Raman spectroscopy (SERS). New GNPs stabilization strategies are developed with industrial surfactants. GNPs stabilized by these surfactants can provide more surface chemistry options as starting points for photothermal therapy. The structure of surfactant cetyltrimethylammonium bromide (CTAB) on the surface of gold nano bipyramid is studied by an analytic method. The method takes a ratio of four peak intensities from two vibration modes of CTAB in SERS and unenhanced Raman spectra. The comparison between the ratios from experiments and simulations is only accurate if conformational variations of the chain are taken into account, thus indicating the importantce of structural fluctuations when using SERS to determine molecular structure. The effect of mixing CTAB with another surfactant, sodium dodecyl sulfate (SDS), and their interactions with gold nanorods (GNRs) are studied. The GNRs are synthesized by a silver-assisted seed-mediated method improved for higher yield and smaller reaction volume. It is observed that SDS together with a tiny amount of encapsulated CTAB can stabilize GNRs. SERS are taken to infer a probable structure that CTA$^+$ cations on the surface of GNRs while DS$^-$ anions form outer layers. GNRs stabilized in SDS are tested for stability in serum and toxicity in cancer cells cultures. The result is compared with GNRs stabilized with CTAB. It is found that GNRs in SDS are stable and do not affect serum while GNRs in CTAB aggregate in serum. Cancer cells in culture medium remain a high viability when GNRs in SDS are injected. On the contrary, cancer cells die when GNRs in CTAB are injected because CTAB is cytotoxic and can solubilize cell membranes. Thus, GNRs in SDS can potentially be applied to photothermal therapy to cure cancer. Conditions and environments for gold nanowire (GNW) synthesis in mixture of CTAB and SDS are tuned and explored. It is found that GNWs can be synthesized in high yield with mono-disperse shape in a 0.1 mm thick and 2 mm wide glass vitro tube. The interaction between surfactants and container surface becomes critical in such narrow space. If methods are developed to take GNWs out of such thin tube, this synthesis idea can be an efficient and convenient way to produce GNWs.