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Toxin detection, in the palm of your hand
JUAN SANTIAGO
rescently label a commercial mixture of ous work in which they developed a When toxic chemicals are released into ⬃1000 carrier ampholytes that have a method to detect analytes indirectly the environment by industrial pollution, transport-related spills, or chemi- (DOI 10.1021/ac701706h). With this wide range of closely spaced electrophoretic mobilities. Then they commethod, fluorescently labeled mobility cal warfare, timely detection is crucial bine the fluorescent carrier ampholytes markers are mixed with the sample for planning an effective response. Bewith the analyte and perform ITP in prior to analysis. During ITP, sample cause environmental scientists need the portable device. “Instead cost-effective detectors that of five fingers, we now have can be widely distributed in 1000 fingers, so we can the field, Juan G. Santiago, achieve both high sensitivity Christopher J. Backhouse, and high resolution of mobiland colleagues at Stanford ity,” says Santiago. University and the UniverIn the current work, the sity of Alberta, Edmonton team demonstrated the por(Canada) developed a handtable device’s ability to detect held device that indirectly two common water pollutdetects unlabeled toxins in ants (2-nitrophenol and water with a fluorescence2,4,6-trichlorophenol) in tap based assay. They report water in ⬃10 minutes, with their results in AC (DOI no prior sample preparation. 10.1021/ac902526g). Currently, the limit of detecThe miniaturized detection for most analytes is ⬃1 tion device includes a microfluidic chip optimized for M, a concentration that is isotachophoresis (ITP), the relevant for the environmencapacity for high voltage tal monitoring of some water Detecting toxic chemicals with a portable device. (A) The FCA asgeneration, and a fluorespollutants. Santiago says that say indirectly detects analytes as gaps in fluorescence during ITP. cence detector. ITP is an the sensitivity could be im(B) Hand-held, USB-powered ITP instrument. (C) Detection of unlaelectrophoretic technique proved by modifying the ITP beled 2-nitrophenol (2NP) and 2,4,6-trichlorophenol (TCP) in tap that separates ionic species microchannel geometry and on the basis of effective elec- water. TE, trailing electrolyte; LE, leading electrolyte. buffer chemistryOstrategies trophoretic mobility. To that his lab plans to explore. ions displace specific mobility markers perform ITP, researchers add an aqueAlthough the researchers did not to produce gaps in fluorescence. ous solution of high-mobility ions, or identify unknown analytes in this “Imagine that the five fingers of your leading electrolyte, to a reservoir at study, they detail in a separate publicahand are fluorescent mobility markone end of a microchannel. Then they tion (DOI 10.1021/ac9025658) how ers,” explains Santiago. “If there’s no add sample dissolved in a solution of this can be done. By performing FCA analyte present, the five fingers arrive low-mobility ions, or trailing electroassays at two pH values, the investigaat the detector one after the other, lyte, to a reservoir at the opposite end tors can accurately estimate the fully with no gaps between them. If you of the channel. When a strong electric ionized mobility and pKa of each anaadd an analyte, it will focus between field is applied, the sample ions milyte. Then they can use these values to two fingers and create a gap in one of grate through the microchannel. “The identify analytes. four places. The width of the gap tells sample ions are squeezed between the “One of the things that is consistent you how much analyte there is, and leading and trailing electrolytes, and with the work done by Santiago’s group is the location tells you its mobility.” electric field gradients focus them into that they develop a very detailed and comA limitation of the fluorescent modistinct zones according to their elecplete understanding of the phenomena bility marker method is that markers trophoretic mobilities,” says Santiago. they are working with,” says David Ross at must be carefully chosen to bracket The most sensitive detection the U.S. National Institute of Standards method for ITP is fluorescent labeling, the electrophoretic mobility of each and Technology. “As a result, they are analyte. In Santiago’s new method, but direct labeling of each sample is often able to push the performance of called the fluorescent carrier aminconvenient. To overcome this chaltechniques beyond the conventional limlenge, Santiago’s group drew on previ- pholyte (FCA) assay, researchers fluoits. In addition, this paper contributes 2596
ANALYTICAL CHEMISTRY /
APRIL 1, 2010
10.1021/AC100324T 2010 AMERICAN CHEMICAL SOCIETY
Published on Web 02/24/2010
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some promising new ideas on how to use fluorescent detection without the complication of having to label the analytes.” According to Michael Breadmore at the University of Tasmania (Australia), “Every now and then something comes
along that makes you wonder why you didn’t think of that. It’s simple, it’s powerful, it’s sensitive, and it’s portableOwhy didn’t I think of that?” But Breadmore notes that identification and quantitation of multiple analytes
will be difficult if the signals for two components overlap. “The question is whether there are enough fluorescent spacers and how different their electrophoretic mobilities are,” he says. —Laura Cassiday
APRIL 1, 2010 / ANALYTICAL CHEMISTRY
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