The fact that the coupling strength (coefficient) varies with the molecular density and the molecular absorption coefficient, as well as with the nature of the resonator when the film thickness is changed, is an essential information for the development of new molecular analysis methods. For example, molecular vibration analysis in the mid-IR was studied in various ways and has been established as a helpful analysis method for molecular fingerprinting for each functional group. Compared with UV-visible analysis, IR spectroscopy is challenging to use for trace analysis because of its low molecular vibration absorption coefficient. However, formation of light-molecule coupling with plasmon metasurfaces has achieved high sensitivity by enhancing the signal inspite of the weak coupling. Such coupling can be observed on the a MIM metasurface of dielectric I-layer of less than 10 nm. The analysis at a single-molecule level can be realized for the polymer. Future studies will consider metasurface as a new platform for molecular detection aiming to establish new vibration analysis techniques based on strong coupling.