Synthesis and stability of chitosan gold nanocomposites: Effect of time of heating and concentration of reactant

Gold nanoparticles (AuNPs) exhibit red colour and is suitable for development of indicators based on colour change. This work investigated the influence of concentration of gold precursor and time of thermal treatment on the properties of chitosan gold nanocomposites. Three concentrations of gold, 5 mM, 10 mM, and 15 mM were used and the heating time studied were 5 min and 15 min. The UV-vis spectra, transmission electron microscopic characteristics, zeta potential, and visible colour were inspected. All the samples have shown distinct colour change and the characteristic surface plasmonic resonance peak at similar to 530 nm. The spectral properties, zeta potential, and particle dispersity were significantly affected by the concentration and time. Furthermore, the nanoparticles were exposed to frozen condition at -18 degrees C +/- 2 degrees C. The absorbance maxima of surface plasmonic resonance peak have changed significantly in all the samples. The visible colour of chitosan gold nanocomposites has changed on freezing and the microscopic analysis demonstrated the clustering and change in shape of nanoparticles on freezing. The results suggest that the chitosan gold nanocomposites synthesised with 10 mM gold chloride and 5 min of heating can be efficiently used as freeze indicator.