Originally Published MDDI September 2005
|Principle of the DNA/RNA hybridization assay. RNA is purified and amplified using a water bath and centrifuge. Organisms are identified by RNA once it has been isolated.|
Detecting pathogens with a handheld biosensor could lead to faster and cheaper diagnosis of diseases, according to a group of researchers from Cornell University (Ithaca, NY).
The device was designed to be used in the field. It was originally developed to identify pathogens in foods and promote food safety, but the researchers believe it can also be
used for medical applications to aid in diagnosis of diseases.
“Applications in clinical diagnostics are immediate; we have shown, for example, that the technology is successful with dengue virus detection in blood samples,” says Antje Baeumner, associate professor of biological and environmental engineering at Cornell.
Unlike current biosensors, which can take up to 48 hours to get results, this device takes about half an hour from beginning to end. “Instead of taking many hours and costing several hundred dollars…the new test should be fully portable—the size of a cell phone—and cost just a couple of dollars for a fast result,” says Baeumner.
The difference is in the testing technique. Most biosensors use gene amplification, a process that takes a DNA sample and adds enzymes to make copies until a pathogen is detected.
The handheld device created by the researchers uses an RNA matching technique and lateral-flow assay. A blood sample is placed in a test tube and heated with an enzyme to break down the cells and release genetic material. A dipstick set to detect a particular microbe is placed in the material for a few minutes. If the pathogen is present, a red line appears on the dipstick.
|Principle of the lateral-flow assay for the qualification of RNA from a pathogenic organism present in a sample.|
The dipstick is impregnated with artificial cells containing sections of complementary DNA sequences that match particular sections of RNA on the pathogen along with a dye. If the RNA is present, it sticks to the dipstick and the dye is activated.
Software designed by lead author Sam Nugen, of Cornell's food and science department, selects the sequences of complementary DNA to match the RNA. For example, the virus responsible for mosquito-borne dengue fever has several sequences on file.
To improve the device, the team is concentrating on being able to perform multiple tests at once. The team can detect all four strains of dengue fever by using several bands on the stick. However, Baeumner says they would like to be able to test for a full range of pathogens at very low concentrations.
Baeumner says that she hopes the technique will be commercialized right away, and believes the device will become a new standard. “We design our sensors for use in doctors' offices, nurses stations in resource-limited nations, or for first responders,” she says. The new sensors can also be used to find biohazards. The research was funded by several federal agencies, including the Institute of Allergy and Infectious Diseases and the Defense Advanced Research Projects Agency.
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