Research article

The influence of epitope availability on atomic-force microscope studies of antigen–antibody interactions

Stephanie ALLEN, John DAVIES, Martyn C. DAVIES, Adrian C. DAWKES, Clive J. ROBERTS, Saul J. B. TENDLER, Philip M. WILLIAMS


The ability of the atomic-force microscope (AFM) to detect interaction forces between individual biological molecules has recently been demonstrated. In this study, force measurements have been obtained between AFM probes functionalized with the β-subunit of human chorionic gonadotrophin (βhCG) and surfaces functionalized with anti-βhCG antibody. A comparison of the obtained results with previous anti-ferritin antibody-binding data identifies differences when the antigen molecule expresses only a single epitope (βhCG), rather than multiple epitopes (ferritin), for the monoclonal antibodies employed. Specifically, the probability of observing probe-sample adhesion is found to be higher when the antigen expresses multiple epitopes. However, the periodic force observed in the adhesive-force distribution, due to the rupture of single antigen-antibody interactions, is found to be larger and more clearly observed for the mono-epitopic system. Hence, these findings indicate the potential of the AFM to distinguish between multivalent and monovalent antibody-antigen interactions, and demonstrate the influence of the number of expressed epitopes upon such binding studies.

  • ferritin
  • force measurements
  • human chorionic gonadotrophin β-subunit
  • protein interaction
  • scanning-probe microscopy