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839-40). "The problem of specificity is usually of major concern in DNA sensors," Willner told Analytical Chemistry. "Our research shows that a 7-base mutation of DNA is easily recognized and differentiated from the target DNA analyte. Thus, ,i seems that our sensor exhibits and reveals high specificity." To increase sensitivity of their device the team devised a way to amplify the microgravimetric signal using antibody technology. Beforehand, they generated antibodies to the double strand of oligonucleotide and by adding these to the sample solution they could boost the frequency change to about 8 Hz as the antibody complexes to the bound T-S strand. The next step in development is to find a way to regenerate the surface monolayer, which will lead to a viable device. Willner adds, "The method of organizing the sensing interface, as well as the QCM transductton, could be applied for the analysis of any other genetic disorder." David Bradley
Biosensor detects estrogen - mimicking compounds A new fiber-optic biosensor for detecting the presence of estrogenic compounds in aqueous samples has been developed at IA in Ann Arbor, MI. The sensor—which wiil be marketed byThreeFold Sensors, a subsidiary of IA— was conceived by John Erb-Downward and brought to fruition by a collaboration between Judith L Erb and co-workers at IA and James L Wittliff and Wolfgang Raffelsberger at the University of Louisville Medical School. According to Judith Erb, the biosensor, referred to as the Endotect system, obtains results in 20 min or less. .n addition to determining whether a compound is ble of binding to an estrogen receptor, the also determines whether a compound is an agonist or antagonist for cific receptor she says The system is portable and offers a quick-screening method for the detection of endocrine disrupters an important class of comDounds believed to cause reproductive and ohvsical abnormalities in wildlife and possiblv in humans The Endotect system relies on binding measurements between a known concentration of fluorophore-labeled estrogen receptor and a chemically sensitized optical fiber. An evanescent field is generated on the surface of the fiber, causing the estrogen receptor to fluoresce. Unbound fluo444 A
rescent receptors exhibit minimal excitation because the evanescent field only extends about 1000 A from the surface of the fiber, says Erb. Receptor binding can therefore be measured without having to separate the bound from unbound receptor she says A sample suspected of containing an estrogenic compound is mixed with the fluorophorelabeled receptor and Endotect system for the detection of estrogenic compounds. introduced into the system bv means of a disposable sensor with compounds that we knew had some cartridge Upon sample introduction sort of estrogenic activity; however, we changes in binding between the receptor have not yet tried it in a real world sample," molecule and the fiber are recorded says Erb. Interferences could occur if something destroyed the receptor, she "The receptor molecule is a recombisays. "It probably wouldn't be great to use nant human receptor, which has been exit on samples coming right out of a pipeline pressed in yeast," says Erb. Therefore only where you might have high concentrations compounds that bind to the human estroof strong acids that would degrade the progen receptor are expected to have a positeins. I visualize two places where it'd be tive response, she adds. very useful," she comments. "The first case Two different sensor fibers are used so is where you know what the compound is that agonists can be distinguished from and you want to determine if it has estroantagonists, says Erb. "Type 1 fibers congen-mimicking capabilities. The other OT16* tain a weak estrogen on their surface, and is where you want to determine if type 2 fibers possess a nucleotide that rething in an environmental sample has posembles the binding region of the nuclear estrogen response element." If a compound tential estrogen activity" decreases binding to a type 1 fiber and inBritt Erickson creases binding to a type 2 fiber, it is likely to be an estrogenic agonist. On the other hand, if a compound decreases binding to a Analyzing phosphine type 1 fiber and either decreases or has no effect on binding to a type 2 fiber, it is at mud flats likely to be an estrogenic antagonist. Although phosphine (PH3) was detected as Injection of the sample mixture into a early as 1927 in sewage purification plants, type 1 fiber will indicate whether the samchemists ignored the investigations, even ple contains a compound capable of affecthushed and fought them. ing estrogen-mediated signal transduction; "Today we know that besides the [inhowever, the system is not intended to dustrial] sources for phosphine, natural identify the compound. "This sensor is dephosphate reduction [also] occurs," says signed for preliminary screening in the Gtinther Gassmann of the Biological Instienvironment," says Erb. "Its response will tute Helgoland (Germany). tell you if there is anything in the sample Natural phosphate reduction was bethat has estrogen-mimicking capabilities. If lieved to be impossible until recently. Gassthe answer is yes, then you start trying to mann was the first in Germany to develop a track down what is causing the positive reliable device to quantitatively measure response," she explains. phosphine in river and marine sediments. His apparatus is a mobiie double-cryotrapping The biosensor exhibits a response to a device with a phosphorus-selective thermivariety of natural and synthetic estrogenic onic detector. Mobility is important for compounds at levels of physiological and him—several times a year he cruises off the environmental interest. "We've tested it
Analytical Chemistry News & Features, July 1, 1998
