Synthesis of metallic nanoparticles protected with N,N,N-trimethyl chitosan chloride via a relatively weak affinity

A water-soluble cationic chitosan derivative, N,N,N-trimethyl chitosan chloride (TMC), was synthesized and used as a stabilizing reagent for the synthesis of highly stable Au, Ag and Pt nanoparticles in a single-phase of neutral aqueous solution. The morphology and stability of metallic nanoparticles were evaluated by transmission electron microscopy and UV-vis spectroscopy. The results showed that well-dispersed metallic nanoparticles have a spherical morphology with diameters of about 3 +/- 0.5 nm. The prepared gold nanoparticles are stable in the aqueous solution ( no significant changes in their morphology and size within 10 months) due to repulsion between the charged polymer shell coatings around the metallic nanoparticles. The relatively low affinity of TMC on gold nanoparticles was confirmed by using a ligand exchange experiment. The mechanism stabilizing the chitosan derivative and the neighbouring gold nanoparticles was identified by FTIR, H-1 NMR and C-13 NMR-measurements.