Plasmonic and photonic refractive index biosensor based on bound states in the continuum

In this paper, we propose a novel structure for biosensors based on a diffraction grating to diagnose
four types of cancers cells. This biosensor is used to detect Hela, Jurkat, PC12, MDA-MB-231 and
MCF-7 cancerous cells, based on their refractive indices. The present configuration consists of a glass
layer covered by a gold layer, a grating coated by a silicon nitride layer separating the sensor from
sensing medium. Bound states in the continuum (BIC) in a hybrid plasmonic-photonic structure can
be achieved at Γ point and off-Γ. The symmetry-protected BIC is formed at the Γ-point of the periodic
system due to the strong coupling between plasmonic or photonic modes. On the other hand, the
Friedrich-Wintgen (FW) BICs can be readily achieved off-Γ due to the strong coupling between
plasmonic and photonic modes. A comparative study is made on the basis of three BICs (plasmonic
BIC, photonic BIC, and FW-BIC). Here, numerical analysis based on the Rigorous coupled-wave
analysis method (RCWA) is performed to optimize the biosensor sensitivity, by also considering the
full width at half maximum (FWHM), detection accuracy (DA), and figure of merit (FoM). TheFW
BIC-based biosensor for photonic mode exhibits the highest S of 1208nm/RIU, lowFWHMof
0.5 nm, the maximumDAof 2 nm−1, and best FoM of 2416 RIU−1.