Preparation of Fe3O4@PMAA-N protein magnetic beads for antibody detection of SARS-CoV-2 based on indirect ELISA smartphone visual strategy.

A novel immunomagnetic bead was prepared and designed to be combined with a smartphone app for the rapid detection of SARS-CoV-2 antibody in serum. The nucleocapsid protein (N protein) of SARS-CoV-2 was immobilized on the prepared magnetic polymer microspheres (Fe3O4@PMAA) with core-shell structure by 1-(3-dimethylaminopropyl)-3-ethylcarbodiimid/N-hydroxy succinimide (EDC/NHS) to form the immunomagnetic beads (Fe3O4@PMAA-NP) capable of binding antibodies specifically. Combining its magnetic separability with the image analysis function of the smartphone app, a novel detection platform was established on a 96-well plate. The platform can realize rapid separation and colorimetric detection of antibodies within 30 min, and the detection limit is 0.5 µg/mL. This method has the advantages of portability, rapidity, high sensitivity and low cost, which is suitable for home self-test and on-site detection. This study not only provides an innovative method for the antibody detection of SARS-CoV-2 in serum, but also provides a favorable reference for the practical application of functionalized magnetic polymer materials in the medical field.