Web Date: March 25, 2009
Ideas Gel For Better Diagnostics
A shape-shifting, gel-making molecule is helping researchers think about ways to improve disease detection, according to findings presented in the Division of Organic Chemistry at this week's ACS national meeting in Salt Lake City.
Gels—which form when molecules self-assemble into networks that pack a lot of solvent—are used in many applications, including regenerative medicine and sensing. Although gels have been studied for nearly 160 years, it's still difficult to design new gel-making molecules, or gelators, from scratch to suit new applications.
Gelator designers usually focus on altering solvent-gelator interactions. But a few researchers instead focus on contacts the gelator makes with itself. "Interactions with the solvent are important but aren't the only factor to think about," says chemist Anne J. McNeil of the University of Michigan, Ann Arbor.
At the meeting, McNeil described her gelator, which emerged from that latter approach. The molecule, a dihydropyridine, forms a gel in response to oxidants such as nitric oxide (NO). The dihydropyridine starts out in a nonplanar conformation, but oxidation makes the molecule snap into a flat shape that, with the help of a newly formed pyridine ring, stacks with neighbors and triggers gelation (J. Am. Chem. Soc. 2008, 130, 16496).
"The use of a redox reaction to induce gelation is very innovative" and could have applications for biomimetic devices, says Brandeis University's Bing Xu, who also designs gelators.
In addition to fleshing out principles underlying gelator design, McNeil's team aims to make gel-based diagnostics. At elevated concentrations, NO in exhaled breath is an indicator of diseases such as lung cancer and tuberculosis. Currently, detecting NO in breath requires extensive luminescence-based detection.
The gel system needs to be made about 1,000 times more sensitive to NO to be feasible for diagnostic use, McNeil cautions. But in principle, since it's easy to see with the naked eye when the material becomes a gel, the method would be operationally simpler than available technology.
At the meeting, undergraduate Tracy H. Lent described unpublished efforts to boost sensitivity with a polymer, and graduate student Jing Chen described how tweaks to the pyridine skeleton affect gelation properties.
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