Simply mixing poly-protein G with detection antibodies enhances the detection limit and sensitivity of immunoassays

The insufficient amount of detection antibodies bound to their antigens usually limits the sensitivity of immunoassays. Here, we describe a simple method to improve the detection limit and sensitivity of various immunoassays by mixing detection antibodies with a soluble poly-protein G (named 8pG). The 8pG was developed by fusing eight repeated fragment crystallizable (Fc) binding domain of streptococcal protein G to a linear polymer. Simply mixing detection antibodies with the 8pG to form an antibody/8pG complex largely increased the accumulation of detection antibody to target molecules, which dramatically enhanced the sensitivity in direct ELISA, sandwich ELISA, Western blot, and flow cytometry systems, separately. The detection limit of the Western blot for low-abundance PEGylated interferon (Pegasys) and recombinant human CTLA4 (rhCTLA4) improved by at least 13 folds and 31 folds, respectively, upon mixing of detection antibodies with the 8pG. Moreover, the nanoscale size of the antibody/8pG complex d...