How SPRi is used to monitor molecular interactions?

SPRi is used to monitor changes of the refractive index occurring at the surface of the SPRi-Biochip. A binding event (or mass accumulation) will induce a change of refractive index and a shift of the position of the resonance angle. SPRi follows the variations of reflectivity occurring at a fixed angle (working angle).

The principle is described in the following diagram:

 

  • Step A: The ligands are immobilized in an array format on the SPRi-biochip surface.
  • Step B: When the sample solution enters the flow cell, molecular binding can occur. This induces a shift of the plasmon curves and a variation of reflectivity. The kinetic curves show the variations of reflectivity versus time. The process can also be monitored on the SPRi difference images. White spots correspond to interacting areas of the SPRi-Biochip.
  • Step C: When the sample solution leaves the flow cell, the ligand-analyte complex dissociates. This induces a shift of the plasmon curves and a variation of reflectivity. The kinetic curves show the variations of reflectivity versus time. The process can also be monitored on the SPRi difference images as interacting spots become darker.
  • Step D: When the ligand-analyte complex is fully dissociated (using a regeneration solution sometimes), the plasmon curves and the kinetic curves return to the initial state. The SPRi difference image is black.
Monitoring of molecular interactions by SPRi
Monitoring of molecular interactions by SPRi