An ionic surfactant-mediated Langmuir–Blodgett method to construct gold nanoparticle films for surface-enhanced Raman scattering

Abstract

A gold nanoparticle film for surface-enhanced Raman scattering (SERS) was successfully constructed by an ionic surfactant-mediated Langmuir–Blodgett (LB) method. The gold film was formed by adding ethanol to a gold colloid/hexane mixture in the presence of dodecyltrimethylammonium bromide (DTAB). Consequently, gold nanoparticles (AuNPs) assembled at the water/hexane interface due to the decrease in surface charge density of AuNPs. Since DTAB binds the gold surface by a Coulombic force, rather than a chemical bonding, it is easily replaced by target molecules for SERS purposes. The SERS enhancement factor of the 80 nm gold nanoparticle film was approximately 1.2 × 10⁶ using crystal violet (CV) as a Raman dye. The SERS signal from the proposed DTAB-mediated film was approximately 10 times higher than that from the octanethiol-modified gold film, while the reproducibility and stability of this film compared to an octanethiol-modified film were similar. This method can also be applied to other metal nanostructures to fabricate metal films for use as a sensitive SERS substrate with a higher enhancement factor.