Aggregation and dispersion of Au-nanoparticle-decorated polystyrene beads with SERS-activity using AC electric field and Brownian movement

Abstract We investigate a novel higher-order nanostructure consisting of Au-nanoparticles-decorated polystyrene beads (AuNPs-decorated PS beads) by the application of AC electric field in a Lab-on-a-Chip scenario to serve a wide range of applications in life sciences, medical diagnosis and environmental analysis. The AC-electric-field-induced dynamic aggregate of AuNuP-decorated PS beads formed a suitable structure for surface-enhanced Raman scattering (SERS). The intensity of the SERS increased with the duration of AC-electric-field application during the aggregation process. This trend is attributed to that the novel hot-spots are formed as dimers, consisting of both AuNPs-decorated PS beads and 4, 4′-bipyridine. On the other hand, during Brownian movement processes, that have no forces derived from AC-electric-field, the SERS signal decreases with time as the dimers randomly disperse. A phenomenological analytical approach based on the dimer formation can reproduce experimental data with respect to aggregation and dispersion processes. This results in the enhancement of external controllability or AuNPs-decorated PS bead aggregation and dispersion. Furthermore, this also results in the production and exclusion of plasmonic hot-spots associated with high Raman enhancement. These results may open future avenues of research and application for strategic SERS analyte detection, in not only Lab-on-a chip for point-of-care testing, but also in-vivo sensing as well as microwave or light therapy.