One-pot bottom-up synthesis of gold nanoparticles mediated by nitrogen-containing polymers: The role of chain features and environmental conditions

The direct bottom-up wet chemical synthesis of gold nanoparticles (AuNPs) via a one-pot two-reactants using exclusively a gold precursor and nitrogen-containing polymers has been herein investigated. The kinetics of nanoparticle formation and the structural features of the polymer-metal hybrids have been probed by using polyethyleneimines, poly(aminoethyl)methacrylates and polyoxazolines acting simultaneously as reducing and stabilizer agents. We demonstrate that AuNPs can be produced in a wide pH range using polyethyleneimines, whereas poly(aminoethyl)methacrylates and polyoxazolines require relatively high pH (pH > 5). This is possibly linked to the degree of protonation of the polymer chains and particularly the presence of unprotonated amine groups in polyethyleneimines even at fairly low pH. The polymer-coated AuNPs can be produced directly in phosphate buffer at pH 7.4 and at room temperature for water-soluble polyethyleneimines and poly(aminoethyl)methacrylates. Nevertheless, polyoxazoline-coated AuNPs were only efficiently produced at 50 degrees C, likely due to the lower electron availability of the amide group as compared to amines of polyethyleneimines and poly(aminoethyl)methacrylates. Depending on the features of the polymer chains, size and shape could be tuned, and larger AuNPs were produced in the presence of poly(2-methyl-2-oxazoline). We have also demonstrated that the chemical nature of the polymer chains has a pronounced effect on the nucleation and growth rates. Yet, all the investigated polymers were able to induce the formation of nearly spherical AuNPs. The reported findings, fundamental in nature, are expected to lead to significant advances towards the facile and ready-to-use production of AuNPs with tunable properties envisaging a myriad of applications.