Bi-Epitope SPR surfaces: A solution to develop robust immunoassays

Abstract

Surface plasmon resonance (SPR)-based immunoassays have numerous applications and require high affinity reagents for sensitive and reliable measurements. We describe a quick approach to turn low affinity antibodies into appropriate capture reagents. We used antibodies recognizing human ephrin type A receptor 2 (EphA2) and a ProteOn XPR36 as a model system. We generated so-called 'bi-epitope' sensor surfaces by immobilizing various pairs of anti-EphA2 antibodies using standard amine coupling. The apparent binding affinities to EphA2 and EphA2 detection sensitivities of the bi-epitope and 'single-epitope' surfaces were then compared. For all antibody pairs tested, bi-epitope surfaces exhibited an ∼10-100-fold improvement in apparent binding affinities when compared with single-epitope ones. When pairing 2 antibodies of low intrinsic binding affinities (∼10-8 M) and fast dissociation rates (∼10-2 s-1), the apparent binding affinity and dissociation rate of the bi-epitope surface was improved up to ∼10-10 M and 10-4 s-1, respectively. This led to an ∼100-200-fold enhancement in EphA2 limit of detection in crude cell supernatants. Our results show that the use of antibody mixtures in SPR applications constitutes a powerful approach to develop sensitive immunoassays, as previously shown for non-SPR formats. As SPR-based assays have significantly expanded their reach in the last decade, such an approach promises to further accelerate their development.