Active Control and Biosensing Application of Induced Chirality between Symmetric Metal and Graphene Nanostructures

Induced circular dichroism (ICD) is found between plasmonic nanostructures and chiral molecules, where at least one of them is chiral. However, it is a great challenge to generate ICD only through achiral structures with the simple coupling model. Here, we demonstrate that ICD is approximately contributed by the cross-electromagnetic coupling between equivalent electric dipole moments and magnetic dipole moments for two achiral plasmon nanostructures. To prove electromagnetic couplings between different wavebands, graphene belts are introduced into plasmon nanostructures composing achiral metal-nanorods with graphene-nanobelt arrays (AMGAs). Results showed that ICD signals are achieved in a near-infrared band of metal resonance and a micron band of graphene resonance. Near-field charge distributions of AMGAs reveal the coupling effect between metal-nanorods and graphene-nanobelts. The handedness of AMGAs can be actively controlled by adjusting the Fermi levels of graphene-nanobelts; the strength and resonant wavelength of ICD can be tuned by adjusting the geometric parameters of AMGAs. Besides, AMGAs can enhance the CD signal of chiral molecules with different handedness. The maximum enhancement factor of chiral molecules could reach up to 800 times in a near-infrared band and 600 times in a micron band. These results are helpful to design dynamically tunable chiral sensors in biological monitoring and analytical chemistry.