Sensor-Based Quick and Precise Method to Detect Chemical Warfare Agents

Sarin is a man-made nerve agent that can spread as a liquid or gas. According to the Center for Disease Control, if exposed to large amounts, muscles and glands will become over-stimulated leading to respiratory failure or loss of consciousness. Even small amounts can cause a long list of distressing and risky symptoms.

“Low-level nerve agent exposure leads to ambiguous signs and symptoms that cannot be easily discriminated from other conditions, which may result in a delay in treatment and permanent damage,” said Paul Braun, professor of materials science and engineering, and director of the Illinois Materials Research Laboratory. “If trace amounts can be detected quickly, you can prevent permanent damage to human health.”

There are sophisticated sensors available, but they are large and expensive, and thus some individuals may be exposed to sarin without knowing it, and that’s too late. Current miniature sensors only show the presence of a toxin, not the amount of exposure.

Paul Braun, Director and Professor of Materials Science and Engineering, Illinois Materials Research Laboratory

Current small sensors also may not be adequately sensitive to provide sufficient protection.

The technology described in this new paper built on earlier work from the Braun group, which had created “chemical black holes” on a small hydrogel surface that attracted molecules toward a point sensor via a chemical potential gradient.

Braun’s group was aware the technology had potential and just needed some more development.

“The problem was that the molecules moved too slowly,” said Braun. “It would take an hour to a day to move molecules a centimeter, and we didn’t have a great way to do quantitative detection.”

However, the chemical black hole method proved that the science behind a chemical gradient would be effective, and the subsequent step was to work out a “detection technique that could make a real impact.”

Acknowledging that they needed something smaller than slow-moving molecules, the scientists exposed a safe version of a sarin-like molecule to the enzyme DFPase, making the molecule to experience hydrolysis, and break up into a number of parts. One of these parts was a negatively charged fluoride ion.

“The fluoride ion is easy to detect electrochemically,” said Mohammad Amdad Ali, a postdoctoral researcher in Braun’s group, and the paper’s first author. “And, because it is so small, it moves much more quickly than a molecule. If we have a surface with positively charged gradient focusing a point in the center of the sensor that really likes (attracts the fluoride ion), instead of taking hours, it takes only minutes for all the fluoride ions to end up at one point.”

We were able to create a gel film that not only broke the molecule down, but pulled the negatively charged fluoride ions into an embedded fluoride ion specific sensor at the center point, and read how much fluoride we had. Once we know how much fluoride we have, we know how much sarin the sensor was exposed to.

Paul Braun, Director and Professor of Materials Science and Engineering, Illinois Materials Research Laboratory

“The fluoride ion specific electrochemical sensor has a low detection threshold, and thus can detect a very low level of fluoride ions,” said Ali. “With the current state of our prototype sensor, we could detect aerosol deposited sarin-like molecule from a vapor concentration as low as 0.01 mg/m³ within 10 minutes,” he added.

The following step is to put the sensors to test in an environment that is equipped to handle the actual nerve agent.

“The ultimate goal is to manufacture something small enough, like a postage stamp, that may be worn on a uniform to detect gas or can be removed to test a surface that within minutes will tell if the agent is present and how much of the agent is there,” said Braun.

“It is not going to tell you about all toxins, but it will tell you about a limited set of compounds very quickly,” he said. “If you find out that sarin is present, you have a much better chance of getting the proper antidote.”

This research was supported by the Defense Threat Reduction Agency and the Department of Defense/US Army.