A one-pot method to prepare gold nanoparticle chains with chitosan

A biocompatible, water-soluble, lower molecular weight chitosan has been used for, via a one-pot high-temperature refluxing strategy, the simultaneous synthesis and assembly of gold nanoparticles. Transmission electron microscopy (TEM) and ultraviolet-visible-near-infrared (UV-vis-NIR) extinction spectra allowed us to identify the existence of nanoparticle linear aggregates. Importantly, through such a preparation procedure, the chain length of the nanoparticle aggregates could be tuned by facile adjustment of the reaction reagent ratio. Further, the growth and assembly processes of gold nanoparticles were studied by quenching the intermediate reaction solutions with an ice-water bath. The structure evolution proceeded through a two-stage process: initial generation of isolated nanoparticles, followed by the interconnection of nanoparticles into an aggregated morphology. A mechanism based on the nonuniform distribution of capping ligands is Z proposed to account for the one-dimensional chain structure formation.