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Chirality of a molecule is of critical importance since it determines the medical functions and biological activity of drugs and proteins. Unfortunately, chiral light-matter interaction is typically weak due to the length mismatch between the wavelength of light and the molecular chiral domain. Plasmonic nanostructures can concentrate optical fields at nanometer scale and provide stiff optical potential to trap nanoobjects, such as proteins or DNAs.
Well-designed plasmonic nanostructures can also sculpt optical near fields so that desired chiral light-matter interactions are enhanced. In work, we theoretically study a novel design of slant-gap plasmonic nanoantenna for optical chirality enhancement. We show by numerical simulations that our slant-gap nanoantenna simultaneously fulfills the three requirements to enhance optical chirality: a) enhanced optical field, b) parallel E and H components and c) a phase shift of π⁄2 between E and H field. Our design, thereby, provides concentrated optical fields with greatly enhanced optical chirality, which is of central importance for chiral light-matter interaction. In typical nanoantennas, the gap is vertical and the enhanced electric field is orthogonal to the external magnetic field, rendering the enhanced field useless for optical chirality enhancement. Our slant-gap nanoantenna resolves this problem and links the resonance-enhanced field in the antenna gap to the optical chirality enhancement. The proposed slant-gap nanoantenna can be easily realized by standard nanofabrication techniques and the excitation scheme can be readily achieved by common optical laboratory. Applications from ultrasensitive CD detection, enantiomeric excess and molecular chirality control to light-induced asymmetric synthesis are anticipated.
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