Poly(N-isopropylacrylamide)-coated gold nanorods mediated by thiolated chitosan layer: thermo-pH responsiveness and optical properties

A core-shell of colloidal metal-responsive polymer provides an innovative model in functional materials. These core-shell nanocomposites offer the possibility to control some properties, such as particle size, surface plasmon resonance and morphology. In this research, we demonstrate the successful synthesis and functionality of gold nanorods (GNR) coated with the polymers chitosan (Ch) and poly(N-isopropylacrylamide) (PNIPAM). The polymer coatings are performed using a two-step method. First, GNR were coated with a thiolated chitosan (GNRCh) by replacing hexadecyltrimethylammonium bromide with a chitosan thiomer. Structural modification of GNRCh was monitored by Fourier transform infrared spectroscopy. Then a second polymeric coating was done by in situ free radical polymerization of N-isopropylacrylamide (NIPAM) on GNR-Ch to obtain the nanocomposite GNR-ChPNIPAM. The nanocomposite average size was analyzed by dynamic light scattering. The evolution of. potentials during the coatings was measured using electrophoretic mobility. GNR-Ch-PNIPAM presented a collapsed structure when heated above the lower critical solution temperature. The particle size of GNR-Ch-PNIPAM was manipulated by changing the pH. Plasmonic properties were evaluated by UV-Vis spectroscopy. Results showed an important blue shift due to the PNIPAM coating thickness. Thermo-and pH-responsive properties of the nanocomposite GNR-ChPNIPAM could be used as a drug delivery system.