Conformational transition in SPR experiments: impact of spacer length, immobilization mode and aptamer density on signal sign and amplitude.

Surface plasmon resonance (SPR) is an optical, real-time and label-free technique which represents a standard to study biomolecular interactions. While SPR signals are usually positive upon recognition, a few cases of negative signals have been reported because of significant conformational transition of the receptor upon the recognition of the target. In this study, we reported on the observation of negative or null SPR signals for an aptamer recognition with its low molecular weight target.