Absolute interfacial distance measurements by dual-wavelength reflection interference contrast microscopy

Dual wavelength reflection interference contrast microscopy (DW-RICM) was used to measure the absolute optical distances between transparent planar substrates and hard or soft surfaces. The technique was combined with a fast image processing algorithm and applied to analyze the trajectories of colloidal beads sedimenting under gravity. It was found that as the beads slowed down due to the hydrodynamic coupling of the bead motion to the substrate as they approached the surface of the substrate. The analysis showed that the DW-RICM technique allowed the determination of height of membranes above substrates and the amplitude and direction of height fluctuations.