(37b) Plasmonic Nanocrystal/Polymer Nanocomposites Thin Films Based Optical Fiber Chemical Sensors

Although a wide range of sensing technologies have been developed for environmental monitoring, there remains a need for an inexpensive sensing platform capable of remote interrogation over large geographical areas with varied terrain or in areas not accessible to conventional sensing technologies. Examples of such applications would include leak detection along thousands of kilometers of natural gas pipelines or plume monitoring of CO₂ sequestration sites. Waveguide-based optical fiber sensors have unique characteristics and flexible designs which make them well-suited to remote monitoring applications due to their inherent long- range transmission of light. We report here a sensitive, reversible, and rapid method of detecting gases such as CO₂ and CH₄ by monitoring changes in the transmitted light intensity within an uncladded optical fiber coated with a polymeric sensing layer capable of adsorbing the target gas. Adsorption of the gas into the sensing layer results in a refractive index (RI) change within the polymer coating. This RI change allows more light from the fiber to be adsorbed by the coating which results in associated loss in transmission at the adsorbed wavelengths. Thus, colored polymers possessing an adsorption band in the visible part of the spectrum allows direct measurement of adsorbed gas concentrations by simply measuring changes in transmitted light intensity through the optical fiber at a wavelength within the polymer visible adsorption band. The sensor can be further tailored through the incorporation of plasmonic nanocrystals into the polymer matrix to allow monitoring at wavelengths commensurate with communication grade fiber optics thereby providing a cost-effective pathway to mass distribution of the sensor platform. A simple method of fabricating NCs-polymer nanocomposite films on optical fibers and the capabilities of these sensor to reversibly detect a wide range of concentrations of CO₂ and CH₄ gases will be presented at the conference.