High-Q quasi-BIC enabled single-nanoparticle virus detection

Bound states in the continuum (BICs) have emerged as a powerful platform for boosting light–matter interactions because they provide an alternative way of realizing optical resonances with ultrahigh quality( Q -) factors, accompanied by extreme field confinement. In this work, we realized an optical biosensor by introducing a quasi-BIC (qBIC) supported by an elaborated all-dielectric dimer grating. Thanks to the excellent field confinement within the air gap of grating enabled by such a high- Q qBIC, the figure of merit (FOM) of a biosensor is up to 18,908.7 RIU −1 . Furthermore, we demonstrated that such a high- Q grating can help push the limit of optical biosensing to the single-particle level. Our results may find exciting applications in extreme biochemical sensing like COVID-19 with ultralow concentration.