Abstract
Chiral molecules show slightly different absorbance of left- and right-handed circularly polarized light (CPL). Such circular dichroism (CD) effect can be used for the characterization of molecular chirality. Unfortunately, CD is usually very weak due to the mismatch between the pitch of CPL helix and the size of molecular chiral domain. Plasmonic nanostructures can concentrate optical fields at nanometer scale and provide stiff optical potential to enhance optical chirality and improve CD signals. Plasmonic elliptical nanoholes can create the concentrated chiral optical near field based on localized surface plasmonic resonance (LSPR). The optical near field generated in nanohole can also provide trapping force to isolate, immobilize and manipulate the target nanoparticles. By controlling the polarization of the incident light, the chirality of the optical near field can be easily switched. Since the optical near field in the hole is circularly polarized, the Raman scattering also reveal the chirality of the target due to the Raman optical activity (ROA). This work is divided into two parts. First, we design and fabricate plasmonic circular nanoholes which are pave with R6G molecules. By measuring the Raman scattering spectrum of R6G molecules in single nanohole, we can then obtain the information between Raman intensity, near field enhancement and transmission enhancement. In second part, we use single nanohole to trap 20 nm polystyrene sphere with high reproducibility in stable state. In the further, combine optical trapping with plasmonic elliptical nanoholes, we are able to obtain ROA analysis by linearly polarized light in solution.