Abstract
The sensitivity of circular dichroism is usually low due to the mismatch between wavelength and molecule size. In this work we use finite-difference time-domain method to calculate and to make sure if the nanoantenna can enhance circular dichroism and optical chirality. It shows that upon linearly polarized excitation, an asymmetry cross antenna serves as a nanosized quarter waveplate and creates circularly polarized near field with highly enhanced intensity inside the gap. Compared with solitary cross antennas, periodic structures are able to enlarge the effective area. Therefore, we design a series of periodic structures. To easily fabricate the antennas, we use diamond shape antennas and fabricate it. On the other hand, the advantage of inverse structure is to make molecules enter the effective enhanced area. We combine the advantage of inverse structure with asymmetry nanostructures to design elliptical nanoholes. Our elliptical nanoholes not only provide plasmonic optical force for trapping small particles but also generate circularly polarized near fields to enhance the signal of circular dichroism.We modify commercial circular dichroism spectrometer for experiment. However, we still haven’t got the reliable result due to the fact that optical elements respond differently to different reflectance of polarized light. In the future, we plan to modify chiral molecules on polystyrene spheres. When exciting elliptical nanoholes by linearly polarized light, we can trap the polystyrene spheres to get the molecular circular dichroism or fluorescence-detected circular dichroism.