Although probably not for the right reasons, in 2020 we have become fully familiarized with the detection of virus antibodies. One of the most widespread methods is the polymerase chain reaction (PCR), which generates billions of copies of any virus RNA present in the sample to reach enough antibody concentration to be detected. However, tests such as PCR require the use of reagents which are not necessarily cheap and an extra step to increase the concentration of the analyte to be able to detect it.
In this publication, the authors propose an antibody detection method that does not require reagents and reduces the testing time. They calculate the concentration of antibodies by measuring very precisely the size of micrometric particles in the sample through the analysis of their holograms. The change in size with respect to the original particle is attributed to the binding of antibodies to them. In addition to providing information on the antibody concentration, this technique can also provide insights into their binding mechanism to the surface of the particles – which are treated with proteins beforehand. Therefore, the replacement of these proteins for others could make these holographic assays targeted for specific diseases.
Comments from the authors:
- Holographic immunoassays detect antibodies by watching them bind to the surfaces of specially functionalized colloidal spheres using holographic video microscopy.
- A hologram of a micrometer-scale colloidal sphere can be analyzed with the Lorenz-Mie theory of light scattering to measure the sphere’s diameter with nanometer precision.
- Comparing populations of spheres before and after incubating with a sample reveals a shift in the mean diameter that can be used to measure the concentration of the target analyte.
- Direct detection through holographic analysis eliminates reagents and processing required for standard bead-based assays, and therefore reduces the cost, complexity and time for each test.
- 20 minute measurements can detect the antibody IgG at concentrations as low as 10 μg/mL and IgM as low as 1 μg/mL.
- Specialized tests for antibodies and virus particles can be programmed rapidly and cheaply by suitably functionalizing the colloidal test beads.
Citation to the paper: Holographic immunoassays – direct detection of antibodies binding to colloidal spheres, Kaitlynn Snyder, Rushna Quddus, Andrew D. Hollingsworth, Kent Kirshenbaumb and David G. Grier. Soft Matter, 2020. DOI: 10.1039/d0sm01351j.
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About the web writer
Dr Nacho Martin-Fabiani (@FabianiNacho) is a UKRI Future Leaders Fellow and Senior Lecturer in Materials Science at Loughborough University, UK.