Narrowband Metamaterial Absorber Based on Plasmonic Square Nanoring for Optical Sensing and Amplification

A plasmonic metamaterial absorber (MA) exhibits unique capabilities of electric field enhancement and spectral modulation and plays a critical role in biosensing applications. In this work, a narrowband MA structure based on a plasmonic square nanoring is designed and numerically investigated. The proposed MA exhibits a high narrowband absorption of 99.77% at a 1216 nm wavelength with a 10 nm full width at half maximum (FWHM). Furthermore, the MA has sensitive absorption properties to the refractive index (RI) of the environment and shows a sensitivity of 186 nm/RIU with a stable value of quality factor around 120 in the RI ranging from 1.0 to 1.4. The sensing and recognition ability of the MA on actual biological cells is also numerically verified. Meanwhile, the proposed MA exhibits excellent capability of fluorescence amplification, achieving 3438–fold fluorescence enhancement at a 1216 nm wavelength with a high directivity of ~590. These properties make the proposed MA structure an excellent candidate for application in an optical sensing system.