Correlation between the composition of multivalent antibody conjugates with colloidal gold nanoparticles and their affinity

Interactions between multivalent preparations of antibodies (conjugated with colloidal gold nanoparticles (GNP) as a carrier system) and a multivalent ligand were investigated. The aim of the present study was to reveal the relationship between the affinity of the conjugate and its composition (i.e., the valency). Surface plasmon resonance was applied to study the affinity and the kinetics of the interaction of multivalent conjugates and multivalent virus (on the example of the plum pox virus (PPV)). Three monoclonal antibodies against PPV were prepared. Five GNP preparations with an average particle size in the range from 5 to 60 nm (according to electron microscopy measurements) were obtained. The series of preparations allowed us to synthesize GNP–antibody conjugates with different surface areas for immobilization of antibodies, and, consequently, conjugates with different valencies. It was shown that the affinity of the conjugates changes with size of colloidal carriers (i.e. with the valency of the conjugates). The affinity of the virus–antibody interaction (antibodies with affinities of 1.46 · 10− 8 M and 1.73 · 10− 8 M) is one to three orders of magnitude lower (depending on the valency of the conjugate) compared to that of the interactions of the virus with GNP conjugates (conjugates with the affinity varying from 1.69 · 10− 9 to 7.02 · 10− 12 M and from 2.39 · 10− 9 to 2.62 · 10− 11 M, respectively). An increase in the conjugate size leads to an increase in its affinity. The similar trends were observed for the potato virus X.