Rapid water/oil interfacial self-assembled Au monolayer nanofilm by simple vortex mixing for surface-enhanced Raman scattering

In this work, a facile surface-enhanced Raman scattering (SERS) substrate formed on a water/oil interface was prepared by adding n-hexane to Au colloids through simple vortex mixing without the involvement of any organic additives. In this process, the background SERS signal was reduced, which is good for the detection of adsorbed analyte molecules on the interfacial substrate. Furthermore, an Au monolayer nanofilm (Au MLF) spontaneously formed at the water/n-hexane interface after just a few seconds of simple vortex mixing, which is much shorter than the time required for self-assembly of nanoparticle films using organic additives. Transmission electron microscopy characterization results showed that the Au nanoparticles are close-packed and that the density of the Au nanoparticles on the interface could be controlled by varying the vortex mixing time and volume of n-hexane. The enhanced Raman signal was mainly as a result of the localized surface plasmon resonance and adsorption enrichment effects. The substrate showed good repeatability, with an relative standard deviation (RSD) of 5.02% (n = 6 × 8) by random selection and an RSD of 5.5% for an area of 4.0 μm × 4.0 μm. Finally, the proposed substrate was successfully applied in the detection of rhodamine B (RhB), malachite green (MG) and ciprofloxacin (CIP), with enhancement factors of 1.1 × 106 (RhB), 0.8 × 106 (MG), and 2.7 × 106 (CIP).