Protein Binders Specific for Immunoglobulin G from Different Species for Immunoassays and Multiplex Imaging

An immunoassay is the most widely used method for analyzing a variety of analytes based on antigen–antibody interactions in the biological and medical sciences. However, the use of secondary antibodies has certain shortcomings, such as a high cost, cross-reactivity, and loss of binding affinity during labeling. Herein, we present the development of repebodies specifically binding to immunoglobulin G with a different origin, which is a small-sized nonantibody scaffold composed of leucine-rich repeat (LRR) modules, for use in immunoassays and imaging. Repebodies specific for IgG from different species (i.e., mouse, human, and rabbit) were selected through a phage display, and their affinities were matured using a modular engineering approach. The respective repebodies were labeled with various signal generators such as horseradish peroxidase (HRP), a fluorescent dye, and quantum dots, and the resulting repebodies were used as alternatives to conventional secondary antibodies in typical immunoassays and imag...