A research team led by R.Graham Cooks has found a way to determine the presence on a surface oftrace quantities of chemicals – such as those found in biological andchemical warfare agents, as well as several common explosives – withina few seconds. The researchers' method uses a tool common in manychemistry and biology labs called a mass spectrometer that has beenmodified to analyze samples directly from the environment rather thanrequiring the lengthy pre-treatment that laboratory mass spectrometrysamples typically require.
According to Cooks, no portable deviceis currently on the market that can analyze samples in this manner. Theteam had previously developed a prototype device that detectsnanogram-sized samples, but with recent improvements the device hasproven successful at detecting at the picogram (trillionths of a gram)level in lab tests, about 1,000 times less material than previouslyrequired.
Cooks said he thinks a portable tool based on the technology could prove valuable for security in public places worldwide.
"Inthe amount of time it requires to take a breath, this technology cansniff the surface of a piece of luggage and determine whether ahazardous substance is likely to be inside, based on residual chemicalsbrushed from the hand of someone loading the suitcase," said Cooks, whois the Henry Bohn Hass Distinguished Professor of Analytical Chemistryin Purdue's College of Science. "We think it could be useful inscreening suspect packages in airports, train stations and other placeswhere there have been problems in the past. Because the technologyworks on other surfaces, such as skin and clothing, as well, it alsocould help determine whether an individual has been involved in thehandling of these chemicals."
J.L. Beauchamp, a chemist at theCalifornia Institute of Technology who has worked in mass spectrometryfor more than four decades, said the team's research on desorptionelectrospray ionization, or DESI, can solve a number of problems.
"Thenature of explosive materials has made them difficult to detect withmass spectrometry," said Beauchamp, who is also a member of theNational Academy of Sciences. "Cooks' group has solved this problemwith DESI, and combined with recent developments in the field hasdeveloped what may be a practical and widely deployable method fordetecting and positively identifying not only explosives, but also awide range of substances that might be employed by terrorist groups."
Theresearch announcement appeared this week as an accelerated article inthe journal Analytical Chemistry's Web site. Cooks developed the methodwith the assistance of his Purdue colleagues Ismael Cotte-Rodríguez,Zoltán Takáts, Nari Talaty and Huanwen Chen.
Mass spectrometersare the workhorses of many chemistry labs because these machines candeliver highly accurate and reliable analyses of substances interestingto scientists, including pharmaceutical developers. The devices alsoare often used by law enforcement to test suspicious looking residuesthat could indicate the presence of explosives or drugs insidepackages. But most mass spectrometers are unwieldy, cabinet-sizedmachines that require samples to undergo hours of intensive preparationbefore testing, which can be a problem if officials need to test alarge number of containers quickly.
"A mass spectrometer is oneof the best tools we've got, but scientists have known for years thatwithout a way to streamline the analytical process, mass spectrometrywill have limited use in the field," said Talaty, a graduate student inCooks' lab. "But with the present technology, we can now analyzesamples rapidly, without any pretreatment. It has already been used toanalyze pharmaceuticals at up to three samples per second."
Cooks'team has made several strides in improving mass spectrometry over thepast few years, having found ways to both decrease the size of thespectrometers and analyze samples rapidly under standard environmentalconditions. Their most recent work with DESI, which involves directinga spray of reactive chemicals onto a surface to dislodge suspiciouschemicals and sucking the mixture into a spectrometer for analysis, hasallowed them to detect hazardous substances at unprecedentedly lowquantities and with equally unprecedented speed.
"Trace andresidue analysis of explosives has been a difficult task due todeliberate concealment, the small quantities of material available andthe presence of other compounds that can interfere with the analysis,"said Cotte-Rodríguez, also a graduate student in Cooks' lab. "But the'spray' technique we use, combined with small tandem mass spectrometersthat can confirm the identity of a particular explosive, gives thismethod both unusual sensitivity and quick turnaround time, evencompared with what we achieved earlier this year."
Talaty saidthe team's forthcoming spectrometry gear, which will weigh less than 25pounds, fits into a backpack and returns a negligible number of falsereadings, both factors that are also important to law enforcementofficials. The small instrument is currently being fitted to work withthe DESI ionization method described in the team's paper.
"Youdon't want to lug around gear that you can't carry on your person, andonce you get it to a site, you want it to give you the straight storyon what you're looking at and be able to confirm it," he said. "Thistechnology can do both."
Although DESI sensors still havedifficulty classifying compounds with many different components, hesaid, this limitation would not likely be much of an issue in bombdetection because explosives do not generally contain that many.
"Ifyou tried to detect a particular compound out of a mixture of thousandsof different substances, you might begin to see the limitations of thismethod," Talaty said. "But real-world explosives are not that complex.In any case, the sensitivity of DESI is high enough that officialscould find what they need to if it's there. No system is flawless, butif we deployed this technology to transportation centers throughout theworld, it would make it far more difficult for terrorists to get awaywith planting bombs where people congregate."
Cooks' team isassociated with several research centers at or affiliated with Purdue,including the Bindley Bioscience Center, the Indiana InstrumentationInstitute, Inproteo (formerly the Indiana Proteomics Consortium) andthe Center for Sensing Science and Technology.
This research was sponsored in part by Inproteo, Prosolia and the Office of Naval Research.
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