Janus-Type\nImmunofluorescent Probes and a Quantitative\nImmunoassay System

To realize highly sensitive immunoassays, high optical\ndensity\nprobes conjugated with antibodies for target antigens have been demanded\nin order to increase the visibility of antigen–antibody complex\nformation. We herein demonstrate the development of an immunoassay\nsystem using magnetic and fluorescent Janus particles as probes in\nconjunction with an antibody-immobilized microfluidic device. The\nconcentration of the detection limit at which there was a significant\ndifference between SARS-CoV-2 and human coronavirus 229E antigens\nwas 3.1 ng/mL, and the standard deviation of the signal was less than\n5%. The immunofluorescent probe and immunoassay system developed in\nthis study are expected to be applicable not only to SARS-CoV-2 but\nalso to the quantitative measurement of various other disease marker\nproteins and biomolecules.