  We fabricated hybrid metal-dielectric nanoantennas and measured their optical
response at three different wavelengths. The nanostructure is fabricated on a
bilayer film formed by the sequential deposition of silicon and gold on a
transparent substrate. The optical characterization is done via fluorescence
measurements. We characterized the fluorescence enhancement, as well as the
lifetime and detection volume reduction for each wavelength. We observe that
the hybrid metal-dielectric nanoantennas behave as enhanced Zero Mode
Waveguides in the near-infrared spectral region. Their detection volume is such
that they can perform enhanced single-molecule detection at tens of microM.
However, a wavelength blue-shift of 40 nm dramatically decreases the
performance of the nanoantennas. We compared their behavior with that of a
golden ZMW, and we verified that the dielectric silicon layer improves the
design. We interpreted the experimental observations with the help of numerical
simulations. In addition, the simulations showed that the field enhancement of
the structure highly depends on the incoming beam: tightly focused beams yield
lower field enhancements than plane-waves.
