Multiplex immunoassays utilize the differential affinities among the conjugation pairs between the capture ligands and target analytes are proposed. Window magnetic-assisted rapid aptamer selection (window-MARAS) methods for selecting aptamers with desirable affinity toward the target analytes and methods for generating reagents for multiplex immunoassays or multiplex detection in one assay by utilizing the selected aptamers as capture ligands in reagents are described and used to demonstrate the feasibility of multiplex immunoassays based on the differential affinity of conjugation pairs between the capture ligands and target analytes.
