Size controllable one step synthesis of gold nanoparticles using carboxymethyl chitosan

Gold nanoparticles (AuNPs) were synthesized by reducing chloroauric acid with nontoxic and biodegradable carboxymethyl chitosan (CMC) as dual roles of reducing agent and stabilizer. Several CMC with different molecular parameters, i.e., degree of substitution (DS), substitution position, degree of deacetylation (DD) and molecular weight (MW) have been investigated for their reducing and stabilizing ability on the synthesis of AuNPs. The obtained AuNPs were characterized with UV-vis spectroscopy, transmission electron microscopy and Fourier transform infrared spectroscopy. The resulting AuNPs displayed controllable size and shape not only depending on the molecular parameters of CMC but experimental parameters, such as reaction temperature, time, pH, concentration of NaOH, HAuCl₄ and CMC in solution. The results indicated the addition of NaOH to a solution containing HAuCl₄ and CMC is essential to synthesize individual spherical AuNPs with a rather uniform size distribution. The -OH at C-6 and -NH₂ at C-2 of CMC played important roles in the reduction of Au(III) to Au(0) and -COO^- groups were accountable for the stabilizing ability of CMC to AuNPs.