Gold nanohybrid systems with tunable fluorescent feature: Interaction of cysteine and cysteine-containing peptides with gold in two- and three-dimensional systems

Abstract Interactions of L-cysteine (Cys), L-cysteinyl-tryptophan (Cys-Trp) and L-glutathione (γ-Glu-Cys-Gly, GSH) with gold-coated surface (Au0) and tetrachloroaurate ions (AuCl4−) were studied in two(2D)- and three(3D)-dimensional systems, respectively. The irreversible bindings of the molecules onto gold surface via gold-sulphur (Au-S) bonds were proven by 2D quartz crystal microbalance (QCM) and surface plasmon resonance (SPR) techniques. Moreover, the cross-sectional areas and the possible orientation of these biomolecules on gold film were also determined and compared with the theoretical calculated values. The spontaneous interactions of Cys, Cys-Trp and GSH with AuCl4− were studied in aqueous medium at 37 °C as well. Depending on the pH and the molar ratios of AuCl4−/molecules, the formation of diverse gold nanostructures were confirmed. It was proven that the spontaneous interactions of AuCl4− with Cys and GSH result in the formation of orange- and yellow-emitting gold nanohybrid systems (λemission = 620 and 590 nm) consist of a self-assembly structure at acidic conditions. In contrast, at alkaline medium fluorescent Au nanostructures were not formed in the AuCl4−/Cys system, but ultra-small blue-emitting gold nanoclusters (Au NCs) were identified in the samples containing AuCl4−/GSH. For AuCl4−/Cys-Trp systems the presence of Trp aromatic side chain prevents the formation of the fluorescence self-assembly nanostructure and depending on the pH, Au concentration and ratio of the reactants the appearance of dipeptide-stabilized plasmonic gold nanoparticles (Au NPs) or supramolecular gold complexes having intense blue fluorescence (λ = 470 nm) were observed