Based on general properties of Maxwell equations, we develop simple design rules to modify the dispersion relation of plasmonic resonators fabricated with nanostructured metallic films, to tune its far field response, and to couple plasmons to phonon polaritons. Appling such rules, a plasmonic trench resonator is designed as an electro-optical biosensor. The resonator is fed by a nanometric slit that can be electrically biased. Light traversing the slit excites surface plasmon polaritons in the resonator that produces high-Q transmission peaks, which are employed for real-time biosensing. Applying and RF electrical bias across the slit, the trench resonator can simultaneously serve as a dielectrophoretic trap able to attract or repel analytes. Trapped analytes are detected in a label-free manner using refractive-index sensing, enabled by interference between surface-plasmon standing waves in the trench and light transmitted through the slit. This active sample concentration mechanism enables detection of nanoparticles and proteins at a concentration as low as 10 pM. The electrically biased split-trench resonator can potentially applied in optoelectronics and for signal processing applications, as well as to trap quantum emitters, paving the way to study strong light−matter interactions, cavity polaritonics, electrical carrier injection, and electroluminescence.
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