Issue Date: August 29, 2011
Diagnostic Device Heads To Field
A new microfluidics-based diagnostic test performs as well as the gold-standard lab-based test at a fraction of the cost, its developers say. They used their “mChip” to detect HIV and syphilis in Rwanda (Nat. Med., DOI: 10.1038/nm.2408).
Despite the many advances that researchers have made in microfluidics, few of those advances have been integrated into a single device that is suitable for use in limited-resource settings in Africa and elsewhere.
To make the mChip, Samuel K. Sia, a professor of biomedical engineering at Columbia University, and coworkers combined advances in manufacturing, fluid handling, and signal detection into a single device.
“Integration has been one of the most difficult challenges” in making field-ready microfluidic devices, Sia says. “We have found that it’s not enough to have a better amplification procedure, or a new method for handling fluids, or a better capture molecule. The real proof is whether we can put together an integrated test that can run from start to finish an accurate assay using real clinical specimens.”
For their test case, Sia and coworkers detected protein markers of HIV and syphilis in 1 μL of whole blood in an injection-molded plastic device. They delivered the 14 reagents—antibodies, washing solutions, and signal-development solutions—needed for the assay using plugs of liquid separated by air spacers. As the solution flows through detection regions on the mChip, antibodies on the channel surface capture protein disease markers from the blood. The researchers amplified the signal using the reduction of silver ions onto antibody-tethered gold nanoparticles. The signal can be observed visually or with an inexpensive optical device. The total cost of materials and reagents is only 10–20 cents per test, Sia says.
Working with clinical collaborators in Rwanda, the team evaluated the device with samples from patients recently diagnosed using lab-based tests. Out of 70 specimens from people with known HIV status, only one tested false. In another study, they used mChip for a combined HIV-syphilis test. The results were as good as those obtained with lab-based immunoassays, with the test for HIV being more sensitive and specific than the one for syphilis.
The disposable mChip “both is simple and carries out the assays well,” says Paul Yager, an engineering professor at the University of Washington who is also developing microfluidic diagnostics. But, Yager also notes, “a bit of support equipment in a permanent instrument is necessary to make the disposable work. My own preference these days is to drop the instrument entirely.”
Sia is working with Claros Diagnostics, which he cofounded in Woburn, Mass., to commercialize the device and assays. “Unfortunately, the return on investment for many global health diseases is not attractive for investors, so we probably need some involvement from philanthropy to commercialize a global health infectious-disease test,” Sia says.
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