Because microarrays can simultaneously detect multiple molecules from a person's body, they hold great promise for individualized diagnosis and treatment of disease. Yet so far, the lab-on-a-chip has struggled to move out of the lab. Now researchers have developed a new microarray platform that offers fast, cheap, and portable sensing capabilities, opening the door for use in the clinic and field (. Chem., DOI: 10.1021/ac101571b).
The U.S. Food and Drug Administration has approved only a handful of microarray tests for clinical diagnosis. These tests, which cost thousands of dollars, require doctors to send samples to remote laboratories for ysis. This makes them impractical for time-sensitive situations such as suspected heart attacks or bioterrorist strikes, says James Herron, a pharmaceutical chemist at the University of Utah.
So Herron and his colleagues developed a new way to read microarray results called in-plane parallel scanning (IPPS). IPPS uses a grid of channels, called waveguides, embedded within the microarray chip. The waveguides direct light to and from spots on the surface of the chip where assays for proteins reside. By measuring the intensity of light exiting from the waveguides, researchers can determine whether or not a specific molecule is present in a sample. In other microarray setups, an expensive laser must scan the entire array, one spot at a time. With IPPS, the gridded microarrays allow scientists to scan only the exits to the waveguides to collect data on multiple spots at once.
Herron's team tested the ability of IPPS to detect two proteins commonly associated with infections acquired in hospitals. Using a standard fluorescent assay, they successfully detected sub-picomolar levels of interleukin-1β, a human protein involved in immune response and inflammation, and Clostridium difficile toxin A, a harmful bacterial protein.
IPPS is not only sensitive, but also fast. "Because we can monitor molecular interactions in real time, in most cases we get enough data to reach a conclusion within 5 minutes," says Herron. In contrast, with existing systems researchers must wait 12 to 24 hours before scanning. The IPPS platform is also much less expensive than laser scanning: about $1000, according to Herron, compared with at least $100,000 for a confocal laser scanner.
The researchers hope to improve the sensitivity and make the microarray system even aller than its current 6 x 3 x 3 inches. In addition, Herron's team is developing medically important assays such as one for the early detection of acute myocardial infarction.
Richard Thompson, a biochemist at the University of Maryland School of Medicine, admires Herron's ingenuity, calling IPPS a "clever, credible way" to quickly detect multiple proteins in samples outside of the lab. He adds: "For sure it's a better mousetrap."
