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Tunable Subradiant Mode in Free-Standing Metallic Nanohole Arrays for High-Performance Plasmofluidic Sensing
journal contribution
posted on 2019-10-08, 20:15 authored by Anran Li, Xiaotian Wang, Lin Guo, Shuzhou LiFree-standing
metallic nanohole arrays (NAs) exhibit extraordinary
benefits in combining nanofluidics and plasmonics in a single platform
for flow-through plasmofluidic sensing. However, the sensing performance
of NAs is usually limited by the low quality factor of the transmission
peak, resulting from strong radiative damping. Here, we demonstrate
a concept for high-performance plasmofluidic sensing based on the
subradiant mode in free-standing metallic NAs. We show that the subradiant
mode exhibits a good spectral resolution only when the dielectric
media at the upper and lower metal surfaces are symmetric; otherwise,
it easily emerges into other features present in the same spectral
region. Therefore, free-standing NAs are particularly suitable for
highly sensitive microfluidic sensing based on the subradiant mode.
In addition, the subradiant mode exhibits a highly tunable frequency
and refractive index sensitivity (RIS), depending strongly on the
film thickness and periodicity and weakly on the hole radius. Compared
with the superradiant mode, the subradiant mode exhibits a much narrower
spectral characteristic and more intensely enhanced electric fields
at metal surfaces with larger field extension and longer lifetime.
The high RIS and good quality factor together afford the subradiant
mode a much better sensing performance than the superradiant one.
This work is significant for developing high-performance lab-on-a-chip
devices.