Hybrid plasmonic nanofocusing waveguide for on-chip SERS tweezer

•The first time to propose a fully-integrated waveguide-based scheme SERS tweezer.•Realize optical trapping and SERS detection simultaneously.•The silicon-based thin tapered waveguide is introduced to compress the mode field.•Nanofocus inside the slot and enhance the electric field.•The SERS tweezer can trap a 20 nm diameter particle with 20 mW power. We design and investigate a hybrid plasmonic nanofocusing waveguide (HPNW) for surface-enhanced Raman scattering (SERS) tweezer applied to the on-chip Raman detection and optical trapping. The input mode from the dielectric waveguide can be well coupled into the surface plasmon polariton (SPP) mode of plasmonic waveguide. During this procedure, the HPNW can compress the mode field, thereby significantly enhancing the spot electric field inside the gold slot, where the SERS can be excited coincided with the optical trapping of sample particles. Meanwhile, the Raman scattered light can be collected by the HPNW itself, without other external devices. The electric field enhancement factor, optical trapping potential and the collection efficiency of scattered light are utilized to study and characterize the performance of the SERS tweezer. The simulation results indicate that the optimized SERS tweezer can trap a 20 nm diameter sample particle with only 20 mW excitation power. As far as we know, this is the first time that the SERS tweezer combining both the SERS detection and optical trapping is proposed in an on-chip photonic waveguide.