Advanced Design of Microfluidic Chip Based on SPP-LSP Plasmonic Coupling for SERS Detection with High Sensitivity and Reliability

In this work, we propose the preparation and investigation of advanced microfluidic surface-enhanced Raman spectroscopy (SERS) chip with a design. allowing high SERS enhancement and analysis reproducibility. The proposed chip implements the creation of periodical metal structure (grating) inside the microfluidic chip and further immobilization of gold multibranched nanoparticles (AuMs) with shaped edges on the grating surface. Such an approach allows achieving plasmonic coupling between the surface plasmon polariton wave, excited on the Au grating, and localized surface plasmon, excited on sharped edges of AuMs. As a result, a high enhancement of electric field in the space between AuMs was achieved, which results in the high SERS enhancement factor, confirmed by both, theoretical calculation and experimental measurements with a typical SERS analyte-R6G. In particular, it is possible to detect a vanishingly small concentration of R6G using the proposed plasmonic coupling, which sensitivity significantly exceeds previously reported limits in the case of microfluidic SERS measurements. We also observed the dependency of SERS intensity on the microfluidic flow rate and demonstrated the perfect reliability of the SERS signal, measured in the microfluidic regimes under constant flow rate.