Subnanometer-Resolution Nanoparticle Sensing through the Strong Coupling between Surface Plasmon Polariton Whispering Gallery Resonances and Localized Surface Plasmon

High-resolution nanoparticle sensing is very important, and many schemes have been proposed to achieve this goal. Circular nanocavities in which surface plasmon polariton (SPP) whispering gallery mode (WGM) resonances were excited were designed to sense particles of ultra-small size and with high resolution. Localized surface plasmon resonances (LSPRs) were excited when a metal particle was set in the circular cavity. The SPP WGM split into symmetric mode (SM) and antisymmetric mode (ASM) due to the LSPRs scattering into the SPPs. The strong coupling between SM resonance and LSPRs generated positive and opposite modes, which were sensitive to the variation in nanoparticle size and position. Even a small nanometer-sized metal particle introduced LSPRs and produced mode splitting. The WGM mode splitting induced by LSPRs reduced the sensing limit. The simulation results show that 1 nm changes in nanoparticle radius and position led to SM 11.8 nm and 10.2 nm wavelength shifts, respectively. This means that variations of 0.09 nm in size and 0.1 nm in position can be sensed with a 1 nm spectral resolution. The strong coupling between SPP WGM and LSPRs can be applied to sense at a subnanometer resolution.

Automated summary

Circular nanocavities were designed to sense ultra-small particles with high resolution using surface plasmon polariton (SPP) whispering gallery mode (WGM) resonances. Localized surface plasmon resonances (LSPRs) were excited when a metal particle was placed in the circular cavity, causing the SPP WGM to split into symmetric mode (SM) and antisymmetric mode (ASM). The strong coupling between SM resonance and LSPRs allowed for sensitive detection of nanoparticle size and position variations, with a 1 nm spectral resolution capable of detecting changes as small as 0.09 nm in size and 0.1 nm in position. The strong coupling between SPP WGM and LSPRs can be applied for subnanometer resolution sensing.