A device consisting of a disk-shaped, Moiré-type plasmonic cavity placed inside a plasmonic crystal cavity, with a 250 nm polymethyl-methacrylate (PMMA) film over the cavities is analyzed by 3D finite-difference time domain (FDTD). Both cavities can be fabricated by Focus Ion Beam, and the waveguide and the Moiré cavity contour can be defined by one-step lithographic process. The device is characterized by calculating the cavity spectrum, the reflection and the radiation spectra and the electric field intensity distribution. It was verified that the transverse-magnetic (TM) input mode generates surface plasmon polaritons (SPP) at the PMMA/gold interface that excites localized surface plasmon polariton on the Moiré cavity, that, in turn, generates reflected waves back to the waveguide and diffracted radiation. Also, the lack of plasmonic crystal bandgap permits the evanescent coupling of Bloch waves to the plasmonic crystal. The high electric field generated by the LSPP on the Moiré surface, and by the Bloch waves at the borders of the plasmonic crystal holes, contributes to the fluorescence of molecules dissolved in the PMMA film. The radiated fluorescence can be detected by a lensed fiber placed above the Moiré surface, and the reflected signal can be detected at the output. © 2012 SPIE.