Key synthesis parameters on preparation of PS@Au nanoshells with chitosan polyelectrolyte

An experimental study is presented of the effect of key processing parameters on the seed-and-grow synthesis of PS@Au nanoshells with chitosan as a surface modifier. The parameters of (1) different seeds, (2) pH of buffer solution, (3) reducing agents and (4) K-gold concentration were studied. The first two are related to the seeding phase whereas the latter two to the growth phase. Carboxylate-terminated polystyrene (PS) spheres were synthesized and then modified by chitosan. Gold seeds of 1–20 nm were prepared and anchored at the PS surface via the NAu bonding for growth of a complete gold shell. Studies show that THPC-gold nanoparticles are favored for seed coverage, and the pH value of the solution is important for surface functionalization. While the reducing agents studied all produce complete Au nanoshells under their respective optimal conditions, the shell quality differs with different reducing agents. For robust synthesis of PS@gold nanoshells, the following conditions are recommended: the THPC-gold particles as seeds, pH of 2.5–3.0, formaldehyde as the reducing agent and a K-gold concentration of 2.5 × 10−4 M. By fine-tuning these parameters, the nanoshells of desired thickness and smoothness can be made. These findings are supported by the TEM images of seed and shell morphologies and by the measured UV–vis spectra of light absorption.