Molecular vibrations that bear information about intrinsic
properties
of chemical compounds are challenging to detect at submonolayer densities.
Surface-enhanced infrared absorption (SEIRA) spectroscopy has been
proven to be a viable approach to enhance and detect weak vibration
signals. Here, we report a SEIRA sensor based on mid-infrared surface
plasmon resonances supported by single-walled carbon nanotubes (SWCNTs).
Due to the 1D nature of SWCNTs, their plasmon modes are highly polarized
with the electromagnetic fields spatially confined to nanometer scales.
Leveraging these characteristics of SWCNTs, we observe a polarization
selective coupling between their surface plasmons and vibrational
modes of chemical bonds introduced onto their surfaces. A maximum
modulation of ∼15% to the plasmon resonance peak is obtained
for a submonolayer chemical group coverage. These findings suggest
that SWCNTs may potentially serve as a highly sensitive SEIRA platform
for revealing intricate information about molecular compositions and
bond orientations.