Multi-Parameter, Remote Groundwater Monitoring with Referencing Using Crossed Optical Fiber Fluorescent Sensor Arrays

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7/1/2006 - 6/30/2008

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  • Peter Geissinger, UW-Milwaukee

Real-time, in-situ measurements of general chemical and physical properties of groundwater are essential for studying the interactions of aquifers with surrounding soils and minerals. Furthermore, measuring contaminant concentrations continually over extended times and spatially resolved is at the heart of investigations regarding the sources of contamination of groundwater as well as the fate of these contaminants due to transport and chemical reactions. We are proposing to apply our recently developed optical fiber sensor platform to groundwater monitoring issues. The sensor platform consists of a rectangular array of junctions of two optical fibers (with adjacent junctions spaced by as little as a few millimeters), at which fluorescent sensors are located. Using pulsed laser excitation and time-resolved detection, every sensor region in the array, in spite of their close proximity, can be read out individually. The sensor molecules are covalently attached to porous gels, which replace the original cladding of the fiber. This sensor active cladding, in turn, is covalently attached to the exposed core of the fiber. Prior to the attachment, the fiber core is functionalized with a hydrophobic, self-assembled monolayer, which in addition to providing attachment sites also protects the fiber core from damage due to hydroxyl penetration through microcracks. This array provides a very general, high-spatial resolution sensing platform, whose functionality depends on the chosen sensor molecules. This proposal focuses on the development of an array that allows for simultaneous, remote sensing of at least two parameters characterizing the aqueous environment of the sensors: pH and oxygen concentration. Additional fiber-fiber junctions provide intensity references to account for fluctuations of the intensity/energy of the probing light pulses. The sensor platform will be integrated into a flow cell allowing for admission of the analyte stream to the sensor regions, with the goal of miniaturizing the platform size for easier deployment.

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