The
design of surface-enhanced Raman spectroscopy (SERS) platforms
based on the coupling between plasmonic nanostructures and stimuli-responsive
polymers has attracted considerable interest over the past decades
for the detection of a wide range of analytes, including pollutants
and biological molecules. However, the SERS intensity of analytes
trapped inside smart hybrid nanoplatforms is subject to important
fluctuations because of the spatial and spectral variation of the
plasmonic near-field enhancement (i.e., its dependence with the distance
to the nanoparticle surface and with the localized surface plasmon
resonance). Such fluctuations may impair interpretation and quantification
in sensing devices. In this paper, we investigate the influence of
the plasmonic near-field profile upon the Raman signal intensity of
analytes trapped inside thermoresponsive polymer-coated gold nanoarrays.
For this, well-defined plasmonic arrays (nanosquares and nanocylinders)
were modified by poly(
N
-isopropylacrylamide) (PNIPAM)
brushes using surface-initiated atom-transfer radical polymerization.
Molecular probes were trapped inside these Au@PNIPAM nanostructures
by simple physisorption or by covalent grafting at the end of PNIPAM
brushes, using click chemistry. The SERS spectra of molecular probes
were studied along various heating/cooling cycles, demonstrating a
strong correlation between SERS intensities and near-field spectral
profile of underlying nanoparticles, as confirmed by simulations based
on the finite difference time domain method. Thermoresponsive plasmonic
devices thus provide an ideal dynamic SERS platform to investigate
the influence of the near-field plasmonic profile upon the SERS response
of analytes.
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