Three-Dimensional Interconnected Network of Gold Nanostructures for Molecular Sensing via Surface-Enhanced Raman Scattering Spectroscopy

Block copolymers have aroused great interest because their self-assembled nanodomains offer access to the fabrication of inorganic nanomaterials with tunable sizes and rich morphologies. In this study, we demonstrate a template-assisted fabrication of three-dimensional interconnected network gold nanostructures (3D-NW AuNSs) for molecular sensing through surface-enhanced Raman scattering (SERS) spectroscopy. To this end, porous templates (PTs) were fabricated by surface-reconstructed films of polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP) micelles. Through immersion in hot ethylene glycol, the PS-b-P2VP PTs are comprised of nanonetworks of branched nanocylinders and interconnected porous channels. Such interconnected nanonetwork structures allow for subsequent adsorption of gold complex ions, nucleation of gold seeds, and eventual growth of AuNSs under the effects of added K2CO3 in aqueous solutions. Two reduction approaches, photoreduction through UV-light exposure at the nucleation stage and chemical reduction by a weak reducing agent at the growth stage, were used. The photoreduction approach has two functions: reduction of gold complex ions to quickly produce single-crystal-like gold seeds and stabilization of template nanodomains. With the template-assisted seeding growth synthesis, the 3D-NW AuNSs have abundant thornlike protruding nanotips and provide a huge surface area for the adsorption of Rhodamine 6G (R6G) molecules. As a result, the 3D-NW AuNSs with protruding nanotips can generate a >109 enhancement factor in SERS and a low detection limit (5 nM) for adsorbed R6G.