  Developing methods to sense local variations in nearby materials, such as
their refractive index and thickness, is important in different fields
including chemistry and biomedical applications, among others. Localized
surface plasmons (LSPs) excited in plasmonic nanostructures have demonstrated
to be useful in this context due to the spectral location of their associated
resonances being sensitive to changes near the plasmonic structures. In this
manuscript, Babinet's principle is explored by exploiting LSP resonances
excited in complementary metal-dielectric cylindrical plasmonic structures
(plasmonic particle-dimers and aperture-dimers in our case). Both plasmonic
structures are evaluated numerically and experimentally using Electron Energy
Loss Spectroscopy (EELS), providing a full physical understanding of the
complementary nature of the excited LSP resonances. The studied plasmonic
structures are then exploited for dielectric sensing under two configurations:
when a thin dielectric film is positioned atop the plasmonic structures and
when the analyte surrounds/fills the plasmonic particles/apertures. The
complementary sensing performance of both proposed structures is also
evaluated, showing the approximate validity of the Babinet principle with
sensitivities values of up to 700 nm/RIU for thin dielectric sensing.
