Evaluation of polymer coatings for ammonia vapor sensing with surface plasmon resonance spectroscopy

Seven 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 with no visible interference from hydrogen sulfide and methane while only minor effects were observed in the presence of up to 24% relative humidity.In addition to probing biomolecular interactions, yielding information relating to binding kinetics, 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 have been discussed as a viable approach to amplifying refractive index changes related to low molecular weight analytes. Gas-phase ammonia was chosen as a test candidate for the coatings evaluated due to its widespread use and health monitoring interest at low-ppm levels. The extent of scientific contributions devoted to monitoring of ammonia further provide a baseline for comparison of the proposed SPR platform with different sensing approaches.