Mirror-enhanced plasmonic nanoaperture for ultrahigh optical force generation with minimal heat generation

Double Nanohole Plasmonic Tweezers (DNH) have revolutionized particle trapping capabilities, enabling trapping of nanoscale particles well beyond the diffraction limit. This advancement allows for the low-power trapping of extremely small particles, such as 20 nm nanoparticles and individual proteins. However, to mitigate the potentially amplified effects of plasmonic heating at resonance illumination, DNH plasmonic tweezers are typically operated under off-resonance conditions.Consequently, this results in a decrease in optical forces and electric field enhancement within the plasmonic hotspot, which is undesirable for applications that require enhanced light-matter interaction like Surface Enhanced Raman Spectroscopy (SERS). In this study, we present a novel design for DNH plasmonic tweezers that addresses these limitations and provides significantly higher field enhancements. By introducing a reflector layer, on-resonance illumination can be achieved while significantly reducing plasmonic heating.This reflector layer facilitates efficient dissipation of heat both in-plane and axially. Furthermore, the integration of a reflector layer enables a redistribution of hotspots via Maxwell's boundary conditions for metals, creating more accessible hotspots optimal for applications that require enhanced light-matter interaction. We also demonstrate low-power trapping of small extracellular vesicles using our novel design, thereby opening possibilities for applications such as SERS and single photon emission that require intense light-matter interaction.