Borodinova T. Formation and growth of gold nanocrystals in aqueous polysaccharide solutions and in primary alcohols mixture

Optimal conditions (composition of solution, temperature and time regimes) have been determined for the formation of flat triangular and hexagonal gold nanoprisms in aqueous solution and in the ethanol-ethylene glycol mixture without admixture of sol particles. It had been established that in the aqueous solution of HAuCl4 exopolysaccharides (EPS) of Chlorella microalgae act as reducer of gold ions and formative and stabilizing factor for gold nanocrystals. In a nonaqueous medium alcohols reduce gold ions to the elemental metal, while stabilizer polyvinylpyrrolidone (PVP) governs morphology of the crystals formed and ensures aggregation stability. We have studied structure, atomic composition, morphology, thickness, surface relief, kinetics and growth mechanisms of nanocrystals. Kinetics of crystallization of gold crystals had been analyzed using Kolmogorov theory. It had been demonstrated by micro-Raman spectroscopy that interaction of EPS molecules with surface atoms of gold crystals takes place via carboxyl and carbonyl groups by donor-acceptor mechanism, and that of PVP molecules - via carbonyl group and nitrogen atom of pyrrolidone ring. Selective adsorption of EPS and PVP macromolecules on {111} faces of gold crystals blocks their growth in the [111] direction resulting in formation of flat nanoprisms characterized by tangential growth mechanism. Studies of Raman spectra of analyte molecules deposited on the surface of gold nanocrystals washed out from the adsorption layer of stabilizer have demonstrated the possibility of their practical utilization as substrates for surface-enhanced Raman spectroscopy. Efficient binding of gold nanocrystals coated with adsorption layer of Chlorella EPS with cell surface of human ovarian carcinoma line А2780S ascertains possibility of their application as cancer cell markers in diagnostics by dark-field optical microscopy.