The characteristics of lysine-mediated self-assembly of gold nanoparticles on the ITO glass

In this study, lysine was investigated as a cross-linker to induce the self-assembly of gold nanoparticles (GNPs) with the variation of solution pH, dosage amounts of lysine, and GNP size. Lysine molecules at acidic pH ranges induced the aggregation of Au colloids via α, ɛ-amine mediated self-assembly of GNPs, consequently leading to the generation of secondary peak at longer wavelength for aggregated GNPs. At intermediate and basic pH ranges, however, the ionization of carboxylic acid groups in lysine hindered the cross-linking between Au colloids with the consequent disappearance of secondary peak. For the array of small Au colloids (ca. 43 nm), lysine induced heavily-aggregated GNPs on the ITO glass at strongly acidic condition (pH2∼3) through its molecular bridging effect. For the array of large Au colloids (ca.70 nm), lysine produced one-dimensional assembly of GNPs on the ITO glass at slightly acidic condition (at pH4.7) through zwitterions-mediated interactions.