What is the difference between QCM-D and SPR measurements?
The ability to evaluate kinetics is quite similar with both systems from a technical point of view, but when it comes to sensitivity they differ quite a lot. QCM-D systems are more sensitive for water rich and extended layers, while the SPR system is favoured for compact and dense layers. The reason to this difference is due to the different physical principles by which the coupled mass is measured. Since the mass-uptake estimate from SPR data is based on the difference in refractive index between the adsorbed biomolecules and water displaced by the biomolecules upon adsorption, water associated with the protein film, e.g. the hydration shell, is essentially not included in the mass determination. In contrast, changes in frequency acquired with QCM-D measures water coupled as an inherent mass via direct hydration, viscous drag and/or entrapment in cavities in the adsorbed film. This means that the SPR response is proportional to the coupled “molar mass”, while in QCM-D measurements the
