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

Abstract

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 ~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 °C ± 2 °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.

Intrinsic properties of chitosan on the characteristics of gold nanoparticles and its application as smart packaging device

“…According to Mitchell et al (2015) the extensive ice crystal growth during freezing reduces the available surface area for interaction of chitosan and gold particles leading to increased aggregation of AuNPs. Sreelakshmi et al (2022) reported effective aggregation of gold nanoparticles and varied morphology of nanoparticles after freezing. When chitosan-stabilised AuNPs aggregate, the colour of the aggregates changes, because of electric dipole-dipole interaction and coupling between the Plasmon's of neighbouring particles in the formed aggregates (Kreibig and Genzel, 1985).…”