One pot synthesis of gold nanoparticles using chitosan with varying degree of deacetylation and molecular weight

Gold nanoparticles (AuNPs) were synthesized in one-step by reducing gold salt using nontoxic and biodegradable chitosan as dual roles of reducing agent and stabilizer. The obtained AuNPs were characterized with UV-vis spectroscopy and transmission electron microscopy. The results indicated that control over the size and shape of AuNPs is achieved through the careful selection of experimental conditions, such as reaction temperature, reaction time, concentration of gold salt and chitosan, and chitosan molecular parameters, i.e., degree of deacetylation (DD) and molecular weight (MW). At low chitosan concentration (0.005% and 0.01% (w/v)), individual spherical AuNPs with average particle size around 10 nm were obtained regardless of chitosan DD and MW, while anisotropic AuNPs were obtained at concentration above 0.05% (w/v) for all investigated chitosan at the optimum condition (1 mL of 1 mmol/L HAuCl4 added to 3 mL of chitosan solution reacted for 120 min at 70 °C). The growth of larger polygonal AuNPs was promoted as the higher concentration and lower DD chitosan was used as reducing agent and stabilizer. Au nanoplate was synthesized by water-soluble chitosan (Mv 566 kDa, DD 53%) at concentration above 0.15% (w/v). Chitooligomers (Mv 2.4 kDa, DD 94%) showed the highest reduction ability for Au3+ and the synthesized AuNPs exhibited aggregation on morphology. It was considered that chitosan DD and concentration played a more important role than MW in the size and shape of AuNPs.