 Reflection-absorption infrared, dual polarisation interferometry, surface-enhanced Raman spectroscopy and sum-frequency generation spectroscopy can be used to probe solid–vacuum as well as solid–gas, solid–liquid, and liquid–gas surfaces.Multi-parametric surface plasmon resonance works in solid–gas, solid–liquid, liquid–gas surfaces and can detect even sub-nanometer layers.It probes the interaction kinetics as well as dynamic structural changes such as liposome collapse or swelling of layers in different pH.