Polymer-Free Side-Patched Gold Nanorods Synthesized via Salt-Assisted Anisotropic Structural Tuning of Silica Shells

The precise and selective modification of the silica shell on the anisotropic structures of gold nanorods (AuNRs) is crucial for advancing their applications in areas such as catalysis, sensing, and directional self-assembly. However, a limitation of existing methods to synthesize patched silica shells on the sides of AuNRs is that they require the introduction of polymeric blocking ligands. Herein, we present a novel method for synthesizing polymer-free, side-silica-patched AuNRs (PF/side-SiO2 AuNRs). Utilizing sodium iodide as the key agent, we achieved a yield of approximately 88%. The underlying mechanism involves the curvature-induced, tip-selective chemisorption of iodide, which reduces the charge attraction between negatively charged silica precursors and the AuNR surface. A comparative study of the localized surface plasmon resonance and surface-enhanced Raman scattering (SERS) properties of PF/side-SiO2 AuNRs with those of conventional silica-coated AuNRs was conducted. The SERS signals of the PF/side-SiO2 AuNRs intensified, whereas interference by the polymeric ligand signals was absent to expose the areas near the hotspots. An efficient technique for synthesizing anisotropic silica-coated AuNRs for various applications is presented herein, and our findings offer mechanistic insights related to the core materials and anisotropic deposition of other oxides.