Ethanol as a 'Catalyst' for Effective Phase Transfer and Self-Assembly of Gold Nanorods

Transferring gold nanorods (GNRs) from an aqueous solution to a non-polar solvent enhances self-assembly, promotes biocompatibility, and boosts surface-enhanced Raman scattering (SERS). However, the strong attachment ability of toxic hexadecyltrimethylammonium bromide (CTAB) to GNRs presents a significant challenge in the fall of CTAB and combining with other substances for self-assembly and SERS applications. We propose a solution that employs ethanol as a 'catalyst' to lower the critical micelle concentration (CMC) of CTAB and efficiently combine it with the organosilanes formed by the hydrolysis of mercaptopropyltrimethoxysilane (MPS) and octadecyltrimethoxysilane (ODS). The samples were characterized by UV-vis-NIR spectroscopy, transmission electron microscopy (TEM), and energy disperse spectroscopy (EDS) mapping. A detailed interpretation of the phase transfer processes was provided. The modified particles were effectively dispersed in toluene and formed thin films at the air-water interface through self-assembly, which was confirmed by scanning electron microscopy (SEM) and optical microscopy. These films can serve as a platform for SERS.