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An Uncommon Sensor

by Sallie Ortiz

spectroelectrochemical sensorA new spectroelectrochemical sensor for monitoring hazardous waste is a breakthrough in sensor technologies because it uses three modes of selectivity instead of the usual one or two of existing sensors. The three modes, from which the sensor derives its name, are spectroscopy, electrochemistry, and selective coating. The new sensor, developed by the University of Cincinnati and the Pacific Northwest National Laboratory, is based on waveguide technology in which a light beam is propagated along the sensor core.

"This is really a fundamental concept, something very new," said Carl Seliskar, Professor of Chemistry at the University of Cincinnati. "It's combining the best of chemistry as is traditionally done over here with waveguide technology, which is traditionally the ballgame of electrical engineering."

The multidisciplinary team includes project lead William Heineman, Thomas Ridgway, Seliskar, and electrical engineer Joseph Nevin, all professors at the University of Cincinnati. Chemist Sam Bryan from the Pacific Northwest National Laboratory has also collaborated on this three-year project funded by DOE's Environmental Management Science Program (EMSP).

"The Department of Energy wanted a sensor they could put in a waste tank and make lots of measurements more quickly, or leave it in there, and monitor what was going on over months or a year," explained Heineman.

Heineman and Seliskar developed a sensor coating that is selective for ferrocyanide, the target compound within the jumbled mix of wastes such as in the Hanford underground waste tanks.

<EM>Hanford Underground Waste Tanks</EM><EM>Tank Waste</EM>







The 177 underground storage tanks (left) were built to hold radioactive waste at the Hanford Site in southeastern Washington State between 1943 and 1985. As a test of its sensitivity, the new sensor was able to successfully detect a specific constituent, ferrocyanide, out of a sample from the jumbled mix of wastes in a tank such this one (right).


"I call these smart materials," said Seliskar. "You can exclude all the things you don't want to measure and include what you do want to measure."

The selective coating only allows certain compounds to enter. For example, all negatively charged ions might be able to enter the sensor while all positively charged ions are excluded. Then the electrochemistry comes into play when an electrical potential is applied, and an even smaller group of compounds are electrolyzed. Finally, a very specific wavelength of light is used to detect the actual compound of interest-in this case ferrocyanide.

Pacific Northwest chemist Bryan assisted the UC team in testing the spectroelectrochemical sensor using actual ferrocyanide-containing waste. The results from the test on the tank waste material were nearly identical to those predicted from tests using a simulant in the university's lab. This result means that the sensor works well with actual contaminated materials.

"We were quite excited about these results and our collaboration with UC. Technology breakthroughs such as this don't happen everyday," said Bryan. "Science is an iterative process and it helps to pool our knowledge. Even researchers who are long retired played a part in this sensor breakthrough."

Bryan and others have been involved in ferrocyanide characterization at Hanford since the 1980s. Initially, ferrocyanide was thought to pose the threat of explosion within the underground tanks, but that fear has since been relieved by the discovery that ferrocyanide completely decays within the tanks. However, because of the knowledge accumulated about this chemical, it made a good target and test for the new chemical sensor to detect within a mix of numerous other constituents.

"We've demonstrated that the novel concept works on a number of systems," said Heineman. "Now, we can move forward with specific applications."

To that end, the EMSP has awarded a three-year renewal of this project to the University of Cincinnati/PNNL team to apply the spectroelectrochemical sensor in remote detection of pertechnetate, a soluble form of the radioactive element technetium that is currently a threat to groundwater near the Hanford Site. For this new grant, PNNL chemist Tim Hubler joined the research team.

Graduate students at UC are also adapting the basic design and concept to monitor other compounds as well. These include glucose monitoring, which would benefit diabetics and offer a less invasive way to monitor premature infants, as well as detection of the toxic pesticide paraquat.

The Environmental Management Science Program is managed jointly by DOE's Office of Science and the Office of Environmental Management. See the EMSP website for more information.

Media Contact: Sallie Ortiz, Pacific Northwest National Laboratory, sallie.ortiz@pnl.gov

Research Contact: William Heineman, University of Cincinnati, William.Heineman@UC.edu
Sam Bryan, Pacific Northwest National Laboratory, sam.bryan@pnl.gov

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