Synthesis of lipophilic gold nanorod superparticles and their size-dependent SERS performances

Gold nanorods are widely used in Surface-Enhanced Raman Scattering (SERS) applications due to their strong localized surface plasmon resonance (LSPR). The self-assembly of gold nanorods further expands their applications and introduces new ensemble properties. In this paper, two types of gold nanorods with similar lengths but significantly different diameters were used for making superparticles. The gold nanorods were first surface-modified with thiol-terminated polystyrene (PS-SH), and then assembled into superparticles through emulsion volatilization. To test the SERS performances of the gold nanorod superparticles, nile red was used as a dye molecule to test the localization of the SERS performance of the single superparticles. It was found that as the size of the superparticles increased, the SERS performances also improved, with the final Raman signal intensity reaching up to 2*10⁶. When the size of the superparticles was the same, the SERS performance was stronger for superparticles composed of gold nanorods with larger diameters. Additionally, a structure similar to the superparticles was designed for FDTD simulations, and the simulated results were highly consistent with the experimental results, further supporting our conclusions.