Unconventional SPR signals: too high or too low magnitude compared to the theoretically expected ones, or even, negative signals are observed in the literature. To better understand and explained this phenomena a new model was developed (J. Phys. Chem. C 2018): in addition to contribution of the target binding to the signal, this model takes also into account the contribution of the ligand conformational change that could induce sensing layer thickness variation and/or the non-additivity of refractive index increments (RII) during the target/ligand complex formation (J. Phys. Chem. C 2019).

Depending to the sensor surface used (2D or 3D with hydrogel matrix), respectively, the left or right equation must be used. This developed model has spin-offs for all optical techniques.