Site-specific Labeling of Antibodies with Quantum Dots Could Promote to Retain the Antigen Binding Capacity of Antibodies.

A major concern with antibody labeling is the decreased antigen affinity binding capacity of antibodies, owing mainly to the randomly oriented binding of the marker. Herein, a universal approach for site-specific photo-crosslinking of quantum dots (QDs) to the Fc-terminal of antibodies was investigated utilizing antibody Fc-terminal affinity proteins. Results showed that the QDs only bound to the heavy chain of the antibody. Further comparative tests confirmed that the site-specific directed labeling approach maximizes the retention of the antigen-binding capacity of the natural antibody. Compared with the commonly employed random orien-tation labeling approach, the directional labeling approach allows the labeled antibody showed 6 times greater binding affinity to antigen. QDs-labeled monoclonal antibodies were applied to fluorescent immunochromato-graphic test strips for the detection of shrimp tropomyosin (TM). The established procedure has a detection limit of 0.054 mu g/mL. Thus, the site-specific labeling approach significantly improves the antigen binding capacity of the labeled antibody.