Detection of anti-SARS-CoV-2 antibody for the diagnosis of past-COVID-19 infection cases using a liquid-crystal-based immunosensor.

Here, we developed a liquid crystal (LC)-based immunosensor for the sensitive and selective detection of anti-severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2) nucleocapsid (N) protein antibodies. LC molecules were aligned parallel to the anisotropic gold nanostructure to induce uniform alignment, and a uniform texture was observed under a polarised optical microscope (POM). After the antigen was immobilised on the nanostructure, the surface was incubated with the antibodies to form antigen-antibody complexes. This led to interference in the uniform alignment of the LC molecules, and a random texture was observed under POM. However, when the surface was incubated with control proteins, the alignment of the LC molecules did not change and a uniform texture was observed under POM. This texture change of the LC optical images was evaluated as quantified values using grey-scale intensity measurements. The lower detection limit was determined to be 100 ng/mL in phosphate-buffered saline (PBS) solution, which is lower than the clinically relevant concentration in the µg/mL range. The developed LC-based immunosensor has high sensitivity and selectivity for the detection of the anti-SARS-CoV-2N protein antibody, which can be easily detected with a small sample volume of 2 µL. [ABSTRACT FROM AUTHOR]