The use of individual fluorescent nanoparticles for imaging molecular-scale biophysics is often hindered by a size-brightness trade-off, where reduced particle volumes lead to diminished signal-to-noise ratios and increased requirements for excitation power. Plasmonic nanotweezers have shown promise in their ability to position and enhance the emission from single nanoparticles. However, traditional designs are typically optimized for a single resonance, failing to simultaneously address optical trapping and emission enhancement. Here, we utilize a multiobjective topology optimization framework to design a dual-resonant plasmonic nanocavity. Our inverse-designed architecture provides simultaneous electric field intensity enhancement for stable optical trapping and Purcell-accelerated emission. Surprisingly, the design strongly resembles a previously reported “antenna-in-a-box” configuration. Simulations demonstrate a 32-fold increase in electric field intensity enhancement at the emission wavelength and a 26-fold increase in the Purcell factor compared to conventional double nanohole designs, while maintaining the gradient forces necessary for stable single-particle localization. This platform offers a robust pathway for high-sensitivity, low-power sensing of diverse nanoscale emitters.
Nelson et al. (2026) studied this question.