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Scientists have put a high precision blood assay into a simple test strip

Researchers from the General Physics Institute of the Russian Academy of Sciences (GPI RAS) and Moscow Institute of Physics and Technology (MIPT) have developed a new biosensor test system based on magnetic nanoparticles. It is designed to provide highly accurate measurements of the concentration of protein molecules (e.g. markers, which indicate the onset or development of a disease) in various samples, including opaque solutions or strongly coloured liquids.

The new development is similar (in its principal) to a pregnancy test. The analysis is conducted using small test strips made of porous material with two test lines. A droplet of the sample liquid is applied to one end of the strip and after a short period the result is shown as the activation of one or both lines. These test strips can be stored for a long time before being used. The test can be done quickly and does not need to be carried out by specially trained staff; tests can easily be performed next to a patient or even in field conditions.

At molecular level, the magnetic nanoparticles “link” with antibodies to the required protein and then they are placed on a porous plate close to the intended point of contact with the test solution. The liquid, which spreads along the plate due to capillary action, captures the magnetic particles. It then meets two lines – the test line and the control line. The test line contains antibodies that capture the protein in question and also the magnetic markers that became attached to molecules of the protein due to the fact that the nanoparticles are also “linked” to the antibodies. The control line only captures the antibodies with magnetic markers, and it will be activated in any case, if the test strip is usable. The control line serves as an indicator as to whether the test is suitable for use, the protein antibodies in it have not been destroyed due to improper storage, and the test liquid has been applied correctly.

After the sample has permeated the test strip and the antibodies have interacted with one another, the result can be read. This is as far as the resemblance to a pregnancy test goes. In a “classic” pregnancy test, the result can either be “yes” or “no”. With this test, however, scientists are not only able to, with a high level of sensitivity, detect a protein, but they can also accurately determine the concentration of the protein. The accuracy of determining the concentration will even exceed the accuracy of methods that are only performed in laboratory conditions by trained staff.

Alexey Orlov, the corresponding author of the study and a Research Fellow of GPI RAS (who also completed an undergraduate degree at MIPT in 2010, and a postgraduate degree in 2013): “Normally, tests that can be performed not only under lab conditions but also in the field, use fluorescent or coloured markers and the results are determined visually, by sight or by using a video camera. In our case, we are using magnetic particles, which have a significant advantage: they can be used to conduct analyses even if the test strip is dipped into a completely opaque liquid, to determine the substances in whole blood for example. The precise numerical measurement is conducted entirely electronically using a portable device. This completely excludes any ambiguity.”

Biosensor-test system
A droplet of the test liquid is applied to the strip (1). The liquid, which spreads along the strip due to capillary action, captures magnetic particles that are “linked” with antibodies to the test protein (2). As they move along the strip, the particles bind to the required protein. The liquid then meets two lines – the test line (3) and the control line (4). The test line contains antibodies that capture the protein and also the magnetic markers that were bound to it. The control line is activated in any case if the test strip is suitable for use
Image courtesy of MIPT Press Service