An international team of researchers from the Eindhoven University of Technology (TU/e; Eindhoven, Netherlands) and Keio University (Tokyo, Japan) has developed a method that involves a glowing paper strip, a drop of a patient's blood, and a digital camera to test for infectious diseases in 20 minutes. The low-cost test has a lot of potential in developing countries to test for tropical diseases easily.
The test shows the presence of infectious diseases by searching for certain antibodies in the blood that the body makes in response to, for example, viruses and bacteria. Not only is the test a low-cost, rapid alternative to expensive, time-consuming laboratory measurements in hospitals, it could also have utility in regularly monitoring the dose of antibody medicines to be able to take corrective measures in good time.
"A biochemical reaction causes the underside of the paper to emit blue-green light," says Eindhoven University of Technology professor and research leader Maarten Merkx. "The bluer the color, the higher the concentration of antibodies." A digital camera—for example, from a cell phone—is sufficient to determine the exact color and thus the result.
The paper strip contains a luminous sensor protein developed at TU/e. After a droplet of blood comes onto the paper, this protein triggers a reaction in which blue light is produced (known as bioluminescence). An enzyme that also illuminates fireflies and certain fish, for example, plays a role. In a second step, the blue light is converted into green light. If an antibody binds to the sensor protein, it blocks the second step. A lot of green means few antibodies and, vice versa, less green means more antibodies.
This paper strip (zoomed in) contains two copies of the test; the three glowing dots per test demonstrate the ability to check on three different antibodies within one test. (Image credit: Bart van Overbeeke)
The ratio of blue and green light can be used to derive the concentration of antibodies. "So not only do you know whether the antibody is in the blood, but also how much," Merkx says. By measuring the ratio precisely, they suffer less from problems that other biosensors often have, such as the signal becoming weaker over time. In their prototype, the researchers successfully tested three antibodies simultaneously, for HIV, flu, and dengue fever. Merkx expects the test to be commercially available within a few years.
Full details of the work appear in the journal Angewandte Chemie.