We theoretically investigate the coupling between a single Ag nanoparticle and chiral molecular J-aggregates (TDBC). The element of the structure is composed of a Ag nanoparticle entirely surrounded by chiral TDBC. The results show that the coupling between the Ag nanoparticle and TDBC can be tuned by the size of the Ag nanoparticle. By changing the size of the Ag nanoparticle, both the strong coupling effect and the weak coupling effect between the Ag nanoparticle and TDBC are achieved. Circular dichroism (CD) spectra of the hybridized structures in both the strong and the weak coupling regimes present a Fano line-shape, which can be represented in the form of ( ϵ + q ) 2 / ( ϵ 2 + 1 ) . We also find that the CD spectrum in the strong coupling regime is less than that in the weak coupling regime. The maximum of the CD spectrum of the hybridized structure in the scattering spectrum is amplified 130 times compared to that of chiral TDBC in the strong coupling regime, and 490 times compared to that in the weak coupling regime, respectively. Much more energy is used to change the resonant wavelength of the hybridized structure in the strong coupling regime. The radiative efficiency of the system is suppressed. In the weak coupling regime, the energy is mainly used to enhance the CD spectrum. Our research has great potential for molecule detection.

We theoretically investigate the strong coupling phenomenon between a quasi-single molecule and a plasmonic cavity based on the blue-detuned trapping system. The trapping system is made up of a metallic nanohole array. A finite-difference time-domain method is employed to simulate the system, and the molecule is treated as a dipole in simulations. By calculating the electromagnetic field distributions, we obtain the best position for trapping a molecule, and we get the strong coupling phenomenon that there are two splitting peaks in the transmission spectrum when the molecule is trapped in the structure, while only one peak is observed in the one without the molecule. We also find that only when the molecule polarization parallels to the incident light wave vector can we observe a strong coupling phenomenon.

We investigate the enhanced chirality of chiral molecular J-aggregates (TDBC) by the propagating surface plasmons (PSPs) in the metallic hole array structure filled with TDBC. The two ends of the hole in the metal film form a low quality factor Fabry–Perot (FP) cavity, and this cavity confines PSPs. The resonant wavelength of the metallic hole array is tuned by the lattice constant and the size of the hole. Both the resonant wavelength of Ag hole array and the volume ratio of TDBC in the hybridized structure influence on the enhancement of the circular dichroism (CD) spectrum. The curve of CD spectrum shows Fano-like line-shape, due to the interaction between the non-radiative field in the FP cavity and the radiative field in chiral TDBC. The maximum of the CD spectrum of the hybridized structure is 0.025 times as the one of the extinction spectrum in a certain structure, while the maximum of the CD spectrum of TDBC is 1/3000 times as the one of the extinction spectrum. The enhanced factor is about 75. The resonant wavelength of the metallic hole array can be tuned in a large wavelength regime, and the chirality of a series of molecular J-aggregates with different resonant wavelengths can be enhanced. Our structure provides a new method to amplify the chirality of molecular J-aggregates in experiments.