Fiber optic immunosensors to monitor small molecule analytes in groundwater

Analytical characterization of environmental sites has become a $1 to $2 billion dollar industry, and field methods to provide lower cost, more rapid analyses are being developed and commercialized. Antibody kits and fieldable gas chromatographs are examples of this work, but they still require extensive manual sample collection and preparation. As a further advance, we are developing a fieldable environmental monitor based on antibodies, fiber optic probes, and compact optoelectronics. Antibodies are immobilized to the surface of etched optical fiber tips, and a displacement reaction between the target molecules and fluor-labeled target analogs is monitored remotely. For extended, autonomous operation, fluor-labeled reagents are contained within a size-selective membrane that surrounds the fiber tip. This creates a small probe head that easily fits within a standard 2" diameter groundwater well. A hand-sized instrument with laser diode, 20-bit A/D, 12 MHz microcontroller, and associated components has also been assembled. Detection limits of 1 ppb for BTEX compounds (benzene, toluene, ethylbenzene, xylene) have been measured. Molecular imprints as lower cost and potentially more durable biomimetic analogs to the antibodies are also being investigated. Preliminary results with toluene and trichloroethylene (TCE) targets have been obtained with molecularly imprinted fiber optic sensors.