Surface plasmon resonance (SPR) as a tool for antibody conjugate analysis

Surface plasmon resonance (SPR) analysis was used to assess the immunoreact ivity of anti-biotin (4) and anti-fluorescein (5) monoclonal antibody after conjugation with the N-hydroxysuccinimide ester of acridinium-9-carboxamid e 1. Only minor changes in the apparent equilibrium dissociation constants of the antibody conjugates for their ligands resulted from the conjugation process. However, comparison of the initial binding rate of the conjugates with their ligands with those of the unmodified antibodies over a range of concentrations showed that the antibody conjugates were partially inactivat ed. The anti-fluorescein conjugates retained at least 90% of their immunore activity over the range of modification tested, while anti-biotin conjugate s showed a progressive loss of reactivity with increased substitution by th e label.