Plasmon-exciton interactions in a spheroidal multilayer nanoshell for refractive index sensor application

We used the finite difference time domain method to calculate scattering spectra for a multilayer nanoshell (MNS) consisting of a gold core, a molecular layer and a gold shell. The effects of geometrical parameters of the multilayer nanoshell (MNS) such as size, aspect ratio, the thickness of the shell and middle layer on the scattering properties of the MNS are investigated. We have also studied the plasmon-exciton coupling. In order to determine the coupling region, our numerical data are fitted to the coupled oscillator model. According to the obtained results, the plasmon-exciton coupling is found in the intermediate region. The plasmon-exciton coupling can be achieved and utilized as a sensor for sensing the refractive index changes. Variation of geometrical parameters of the multilayer nanoshell affects the strength of coupling and hence the sensitivity and detection accuracy of the sensor. The understanding of coupling mechanisms paves the way for the optimal design of the proposed sensor. We finally quantify and compare the performance of the sensor against previously introduced similar sensors.