Plasmonic Chiral Metamaterials with Sub-10 nm Nanogaps.

Sub-10 nm nanogaps are enantioselectively fabricated between two nanocrescents based on nanoskiving and show tailored circular dichroism (CD) activity. The mirror symmetry of the nanostructure is broken by subsequent deposition with different azimuthal angles. Strong plasmonic coupling is excited in the gaps and at the tips, leading to the CD activity. The dissymmetry g-factor of the chiral nanogaps with 5 nm gap-width is -0.055, which is 2.5 times stronger than that of the 10 nm gap-width. Moreover, the surface-enhanced Raman scattering (SERS) performance of l/d-cysteine absorbed on chiral nanogaps manifests as the emergence of enantiospecific Raman peaks and the appearance of distinct changes in SERS intensities, which affirms that chiral nanogaps can recognize specific cysteine enantiomers via standard Raman spectroscopy in the absence of circularly polarized light source and a chiral label molecule. The sub-10 nm chiral nanogaps with tailored chiroptical responses show great potential in a class of chiral applications, such as chiral sensing, polarization converters, label-free chiral recognition, and asymmetric catalysis.