In the January/February 2018 issue of Elektor, a clock was described that wrote the time with a laser on ‘glow-in-the-dark’ material. This principle of luminescence can, however, also be used to test for infectious diseases.

Researchers from Eindhoven and Japan have developed a practical and reliable method to carry out such tests. You only need a special glowing paper strip, a drop of blood and a digital camera. This makes the technology very cheap and fast: after twenty minutes it is clear whether there is an infection. Expensive and time-consuming laboratory tests in a hospital are not necessary. In developing countries too, this test has great potential for the easy testing for tropical diseases.

Antibodies

The test indicates the presence of an infectious disease by looking for certain antibodies in the blood. These antibodies are produced by the body in response to, for example, viruses and bacteria. The development of handy tests for the detection of antibodies receives a great deal of interest, as an alternative for expensive, time-consuming laboratory tests in hospitals. Doctors also increasingly use antibodies as medicines, for example in cases of cancer or rheumatism. This simple test is therefore also suitable to periodically check the dose of such medicines and to allow for timely corrective action.

Paper gives light

The usage of the paper strip that the researchers from TU Eindhoven and the Japanese Keio University have developed, is a piece of cake. Place a drop of blood in the appropriate place on the paper, wait twenty minutes and turn it over. A biochemical reaction causes the underside of the paper to emit a blue-green light. The more blue the colour, the higher the concentration of antibodies. A digital camera, in a mobile phone, for example, is sufficient to determine the exact colour and therefore the result.

Sensor protein

The colour is generated thanks to a secret ingredient in the paper strip: a luminous sensor protein developed at the TU/e. After a drop of blood is placed on the paper this protein starts a reaction that produces blue light (also known as bioluminescence). A role is played by an enzyme that also illuminates, for example, fireflies and certain fish. In a second step, the blue light is converted to green light. But here comes the clue: if an antibody binds to the sensor protein then it blocks the second step. A lot of green therefore means few antibodies, and the other way around. The ratio of blue and green can therefore determine the concentration of antibodies.

The research has been published in Angewandte Chemie.