A novel process to prepare a thin silica shell on the PDDA-stabilized spherical Au nanoparticles assisted by UV light irradiation

Abstract

A modified polyol process is a convenient route to prepare monodispersed, uniform spherical Au nanospheres stabilized by Poly Diallyl Dimethyl Ammonium Chloride (PDDA). However, Au nanospheres with PDDA coatings possess a high zeta potential and such PDDA coatings can not be removed easily, leading to a difficulty in coating a silica layer on surfaces of Au nanospheres, further resulting in the limitation of the applications of these monodispersed Au nanoparticles (NPs). Herein, we develop a novel route to coat a silica layer on PDDA stabilized Au nanospheres assisted by UV light irradiation without the use of a silane coupling agent as the surface primer. PDDA-stabilized Au nanospheres showed high a positive zeta potential (36.7 mV), which is disadvantageous to coat a layer of thin silica shell. In our strategy, UV light irradiation with high power was applied to PDDA stabilized Au nanoparticles and part of PDDA on Au nanoparticles was degradated, producing lower positive zeta potential (14.7 mV), which guaranteed that silica shell could be easily formed on the surface of Au sphere under such a low zeta potential. The thickness of silica shell could be successfully tuned from 2 nm to 8 nm by adjusting the concentration of TEOS. As far as we know, this is first report to coat the silica layer on PDDA stabilized Au nanospheres. Such monodispersed Au spherical nanoparticles with controlled silica coatings could be extended to important applications in SERS applications, electrochemistry after self-assembled into monolayer particle arrays.