Silica-coating and hydrophobation of CTAB-stabilized gold nanorods

A novel silica-coating procedure that has been devised for cetyltrimethylammonium bromide (CTAB)-stabilized gold nanorods was illustrated. The method comprises a combination of the polyelectrolyte layer-by-layer (LBL) technique and the hydrolysis and condensation of tetraethoxy silane (TEOS) in a 2-propanol-water mixture and leads to homogeneous coatings with tight control on shell thickness. Two polyelectrolyte layers have been found to completely screen the effect of CTAB on gold nanoparticle surface. Coating of Au nanorods has been demonstrated but the protocol can be readily extended to other CTAB-capped nanoparticles and opens a new avenue for further processing through silica coatings. The results show that the aspect ratio decreases upon growth of the silica shell and it is expected that spherical silica particles with controlled optical response in the visible and NIR can be created for fabrication of sophisticated photonic structures.