Circular dichroism (CD) is helpful in providing useful knowledge about the structure of biological macromolecules. However, CD generated by intrinsic chiral materials is always too weak so it is inefficient to probe the micro-structure of biological molecules. To enhance the CD signal, chiral metamaterials composed of artificial meta-atoms with controllable chirality, have been developed in the past few years. Besides chiral metamaterials, recent theoretical and experimental results have shown that planar metasurfaces can also lead to CD at oblique incidence. In principle, both absorption and scattering of circularly polarized light contribute to CD. Nevertheless, scattering of incident left and right circularly polarized light can be an important contribution to the CD of the molecules, whose dimensions are greater than 1/20 of the incident wavelength. Therefore, abnormal scattering will induce a considerable CD.