Specific Binding of Antigen-Antibody in Physiological Environments: Measurement, Force Characteristics and Analysis

The specific recognition of the antigen by the antibody is the crucial step in immunoassays. Measurement and anal- ysis of the specific recognition, including the ways in which it is influenced by external factors are of paramount significance for the quality of the immunoassays. Using prostate-specific antigen (PSA)/anti-PSA antibody and ?-fetoprotein (AFP) /anti-AFP antibody as examples, we have proposed a novel solution for measuring the bind- ing forces between the antigens and their corresponding antibodies in different physiological environments by combining laminar flow control technology and optical tweezers technology. On the basis of the experimental results, the different binding forces of PSA/anti-PSA antibody and AFP/anti-AFP antibody in the same phosphate- buffered saline (PBS) environments are analysed by comparing the affinity constant of the two antibodies and the number of antigenic determinants of the two antigens. In different electrolyte environments, the changes of the binding force of antigens-antibodies are explained by the polyelectrolyte effect and hydrophobic interaction. Furthermore, in different pH environments, the changes of binding forces of antigens-antibodies are attributed to the role of the denaturation of protein. The study aims to recognise the antigen-antibody immune mechanism, thus ensuring further understanding of the biological functions of tumour markers, and it promises to be very useful for the clinical diagnosis of early-stage cancer.