Tunable Nanorods Aggregation Using Acoustic Streaming Tweezers for Surface-enhanced Raman Scattering

Surface-enhanced Raman scattering (SERS) is a highly sensitive technique that can provide enhanced Raman signals from nanostructures (e.g. nanorods). Controlling the ‘gaps’ between the nanostructures is extremely important since the Raman scattering signal is closely related to the separation distance of the metallic nanostructures. In this work, we applied acoustic streaming tweezers (AST) to control the aggregation status of the gold nanorods (AuNRs) in liquid phase, which provides a novel method to enable dynamic SERS. Using 4-Mercaptobenzoic acid (4-MBA) as model Raman reporter, the intensities of Raman peaks were significantly enhanced by ~30 times after AST-induced aggregation, proved the feasibility of the AST-based SERS strategy. Furthermore, the Raman intensity increased accordingly under a series of increasing applied powers of the bulk acoustic wave (BAW) resonator, revealing that the gaps between AuNRs can be adjusted by AST to achieve the liquid-phase dynamic SERS, which will be of potentially significance in the wide use of SERS and biosensing applications.