Single nanoparticle detection based on a slotted nanobeam cavity

In this work, a single nanoparticle sensor based on a slot-bridge-slot photonic crystal nanobeam cavity is presented. To investigate the sensor feasibility of a single particle detection, the shift of the resonance wavelength of the cavity mode is calculated by employing perturbation theory and the simulation results of the mode profile. A mode volume of $2.61\times {10}^{-3}{\left(\lambda /n\right)}^3$is realized, which is reduced by a factor of $150$ times in comparison with nanobeam cavity. We demonstrate the detection of streptavidin molecules with radius ∼ 2.65 nm with a large resonant wavelength shift (25.4 pm). This represents the largest wavelength shift ever reported in single nanoparticle sensors. Owing to the ultracompact footprint and high sensitivity demonstrated here, the proposed structure holds great potential for lab-on-a-chip biosensing applications.