University of Tennessee researchers have developed a lab-on-a-chip device for label-free detection of protein biomarkers that they say could prove a quicker, less expensive alternative to conventional ELISAs.
According to UT scientist Shigetoshi Eda, one of the device's inventors, in early proof-of-concept studies in Johne's disease and bovine tuberculosis it demonstrated accuracy comparable to conventional immunoassays, but much more rapidly and at much lower cost.
The device consists of an array of interdigitated microelectrodes functionalized with bait proteins that bind target analytes. Researchers can detect this binding by measuring changes in impedance between these microelectrodes, making the assay label-free.
The device also uses the microelectrodes to induce AC electrokinetic effect – ACEK – which draws molecules in the sample of interest toward the bait protein attached to the electrode. This accelerates the binding process and reduces the necessary incubation time to as little as two minutes – compared to an hour or more for conventional ELISAs.
Previous microfluidic devices have used ACEK for moving sample through the chip, Jayne Wu, UT associate professor of computer science and electrical engineering and co-developer of the device, told ProteoMonitor. However, using it to reduce incubation time is a new application, she said.
Thus far, Wu said, the researchers have focused on using the device for veterinary applications, a setting in which reduced incubation time could prove particularly useful.
"If you have a way to detect [disease] in minutes you can determine if a cow or goat is sick on the spot and you can isolate it," she said. "Otherwise you have to take a sample and then wait for a week [for it to come back from the lab], and in the meantime that animal is roaming free."
Johne's disease, or paratuberculosis, is a chronic infectious disease affecting ruminant animals. Currently, it causes more than $200 million in annual losses to the US dairy industry, Eda said.
Early diagnosis is key to preventing and containing the disease, but due to the cost, time, and labor involved in conventional testing, farmers typically test for it only once a year, he told ProteoMonitor.
With conventional tests, "you need to send out samples to a lab and then it takes about a week until you get them back and know whether the animal is infected or not," Eda said. The UT device, on the other hand, would provide results on site in a matter of minutes, making testing much more convenient. It would also cost less than $1 per test, he said, compared to $5 to $7 per sample for conventional ELISAs.
The device's speed could prove a significant advantage in bovine tuberculosis testing, as well, Eda said. The current test for the disease is a skin test that requires injecting TB antigen into an animal and then waiting several days to see if there is an immune response. This wait time is inconvenient with regard to testing livestock, but it is an even more significant obstacle to testing wild animals, which serve as a reservoir for the disease, he said.
"There is concern that wild animals are transmitting [bovine TB] to livestock, so there is need for a diagnostic test [for wild animals]," he said. "A skin test isn't really practical for that because you need to capture the animal, inject the antigen, and then keep the animal for two or three days. But with this device you can test in two minutes. That would make a very big difference."
For the Johne's disease and bovine TB test, the researchers functionalized the chips with antigen to detect antibodies for those diseases in samples. They have used it for more traditional biomarker detection workflows, as well, testing for dairy cattle pregnancy by functionalizing the chip with an antibody to bovine pregnancy-specific protein B.
The Johne's disease and TB testing work builds on previous research by Eda on extracting and purifying surface antigens from the bacteria that cause these diseases. In a 2006 paper in Clinical and Vaccine Immunology, he demonstrated that isolating these antigens allowed for development of highly sensitive and specific tests.
"For Johne's disease, for example, current ELISAs have around 20 percent sensitivity," Eda said. "Our test [using his antigen preparation technique] can detect it at better than 80 percent sensitivity. So the use of the antigen [prep technique] is a very big advantage."
The UT researchers have a provisional patent on the device, and are in talks with several companies and venture capitalists about commercialization plans, Wu said, although she didn't name any specific firms. The team recently received $15,000 from the UT Research Foundation to further develop the technology.
While the device is applicable to human disease, Eda said the researchers plan to focus initially on commercializing it for use in a veterinary setting.
"We're going to first focus on animal diseases because it's faster to commercialize tests for that than for human health applications," he said. "But the technology can be easily adapted for diagnosis of human diseases."
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