Strong superchiral fields and an ultrasensitive chiral sensor of biomolecules based on a dielectric photonic crystal slab with air holes

Detection and quantification of chiral enantiomers of biomolecules are of considerable importance for biomedical diagnostics and pathogen analyses. However, the chiral signals from natural molecules are typically small and weak; a long measuring time and a large amount of samples are needed to fulfill the detection limit for the present technique. How to improve the detection efficiency for realizing ultrasensitive probing of chiral molecules has become a key problem. Here we propose a scheme to perform ultrasensitive detection of chiral molecules based on degeneracy states of orthogonal polarization modes in the achiral dielectric nanostructure. The degeneracy states are realized by designing dielectric photonic crystal slabs with air holes. Based on such degeneracy states, homogeneous superchiral fields of both handednesses over arbitrarily large areas can be obtained in a wide spectral range, resulting in the enhancement of the circular dichroism signal by more than three orders of magnitude, thus paving the road toward ultrasensitive characterization and quantification of molecular chirality.