A Severinghaus-type CO<sub>2</sub> sensor was prepared for in-situ downhole CO<sub>2</sub> monitoring during
geological carbon sequestration. The sensor consists of: a porous support material; gas-permeable
membranes coated onto the inner and outer surface of the support material; a metal-oxide
electrode and a reference electrode; and an internal electrolyte composed of equal amounts of
bicarbonate source and a halide salt. The sensor was tested by measuring the output potential
between the metal-oxide electrode and the reference electrode. The prepared CO<sub>2</sub> sensor
demonstrated an excellent linear interrelation between the sensor response potential and the
logarithm of the CO<sub>2</sub> concentration at high pressure. A microcontroller-based data acquisition
system was designed for downhole CO<sub>2</sub> sensor data logging, which could convert the sensor's
analog signal to a digital signal without discharging the sensor during data collection.
A zeolite-fiber integrated chemical sensor was developed for in situ point detection of chemical warfare agents. The sensor was made by fine-polishing the MFI polycrystalline zeolite thin film synthesized on the endface of the single mode optical fiber. The sensor device operates by measuring the optical thickness changes of the zeolite thin film caused by the adsorption of analytes into the zeolite channels. The sensor was demonstrated for sensitive detection of toluene and dimethyl methylphosphonate (DMMP).
A new type of optical chemical sensor recently developed in our lab has been demonstrated for highly sensitive, in-situ detection of explosives. The sensor is comprised of a dense silica thin film grown on the straight-cut endface of a standard, 125μm telecommunication optical fiber. Silicalite is an all-silica MFI-type zeolite with an effective pore size of 0.55nm. MFI zeolite is highly hydrophobic and selectively adsorbs organics of appropriate molecular size. The sensor device operates through measuring the optical refractive index or optical thickness of the coated zeolite film which changes in response to the adsorption of molecular species in its crystalline structure. In this work, the sensor exhibited different responses to simulants including pxylene, o-xylene, and triisopropylbenzene and trinitrotoluene (TNT) trace vapor in helium carrier gas.