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21 Aug 2018
Chalmers University of Technology researcher Mikael Käll discusses technology that could help counter novichok-type threats.
by Ford Burkhart in San Diego
In the face of terrorist threats and recent novichok attacks in the UK, a Swedish researcher has outlined a potentially life-saving way to detect traces of chemical warfare agents whose identification currently requires sophisticated laboratory equipment.
In a SPIE Optics + Photonics symposium plenary session dedicated to nanoscience and engineering, bionanophotonics expert Mikael Käll from Chalmers University of Technology in Gothenburg, Sweden, explained how plasmonic nanostructures can detect nerve agents at super-low concentrations.
The spectroscopic approach uses a handheld surface-enhanced Raman scattering (SERS) tool, based around light scattered from substrates of flexible, gold-covered silicon nanopillars.
“It’s rather simple, straightforward and cost effective, yet still highly sensitive,” Käll told attendees at the San Diego Conference Center.
Although this particular technology has not yet reached the product development stage, he added that researchers in Denmark are pursuing commercialization of similar SERS substrates.
Tabun and VX
Käll illustrated label-free molecular fingerprinting that he said outperforms earlier tests for deadly nerve agents including VX and tabun. Developed during World War II, tabun is chemically similar to sarin and the novichok family. A cocktail of mustard gas, tabun, VX, and sarin is believed to have been used in the infamous chemical attack on Kurdish civilians in Halabja, Iraq, in 1988.
According to Käll, the SERS method has succeeded in detecting nerve agents at aqueous concentrations five orders of magnitude lower than is possible with conventional techniques. Detection limits were estimated at around 13 and 670 femtomol, respectively, for VX and tabun.
Certain novichok variants, thought to be the most lethal nerve agents ever devised, are nearly an order of magnitude more lethal than VX - meaning that even tiny traces of the chemicals can be deadly.
The Chalmers researcher also described areas of high droplet adhesion and nanopillar clustering on the substrate surface, due to elasto-capillary forces and resulting in enrichment of target molecules in plasmonic “hot-spots” - in turn yielding high Raman signal enhancement.
“The key to the whole thing,” he noted, “is that this is simpler and cheaper than traditional methods.”
Pharmaceutical driver
Meanwhile, there is a growing community of researchers investigating the nano-optical properties and potential applications of dielectric nanoparticles made from high-refractive-index materials like silicon.
Käll cited three examples applying his own work, namely: analysis of protein antibodies in diagnostic and biological research; viewing antigen interactions at the single-molecule level; and studying single lipid-molecule diffusion in artificial cell membranes.
More broadly, Käll said: “By looking at the kind of rotational dynamics that we observed with optically tweezed nanorods, you can investigate a lot of fundamental, non-equilibrium thermodynamics.”
Among the key drivers for better molecular detection and analysis through plasmonics is the potential for applications in pharmaceutical industry, while uses in solar cell production, and a variety of quantum applications enabling new communication devices are also on the horizon.
“We have learned how to fabricate the silicon particles used for sensing,” Käll concluded. “This combination of steps brings good opportunities for future research.”
About the Author
Ford Burkhart is a writer based in Tucson, Arizona.
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