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Several polymeric membranes were evaluated for their potential to improve the sensitivity and impart chemical
selectivity to surface plasmon resonance (SPR)-based sensors. The membranes tested encompass a variety of deposition
methods, providing an insight of the contact requirements between polymers and the plasmon supporting metal. Among
the membranes evaluated, preliminary results utilizing polyelectrolyte multilayer membranes displayed reliable detection
of vapor-phase ammonia at ~40 ppm levels. Chemically synthesized polyaniline also presented encouraging results,
responding to ammonia gas at 48 ppm. This is in sharp contrast to the electropolymerized counterpart, which showed
minor wavelength shifts even at elevated ammonia levels (4 %).
SPR has been adopted by the bioanalytical community to probe biomolecular interactions and obtain information relating
to binding kinetics. Similarly, modifying plasmon-supporting surfaces with bioreceptors enables access to biosensing
applications. Gas-phase sensing with SPR has largely remained unexplored primarily due to the small changes in
refractive index from low molecular weight molecules. Coating SPR sensors with tailored polymers has been discussed
as a viable approach to amplifying refractive index changes related to low molecular weight analytes.
Ammonia is a low molecular weight analyte that is ubiquitously present in the gas phase. Industrial and medical interest
in ammonia at low ppm level yielded numerous scientific contributions describing diverse sensing approaches. Hence,
ammonia is a good candidate to provide a baseline for immediate comparison with other approaches for evaluation of the
polymers with regards to their susceptibility to undergo changes in dielectric properties and chemical affinity for the
analyte.
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