RIfS is a non-destructive, label-free, and versatile technique in liquid and gaseous phases, that is well suited for monitoring biomolecular interactions. Reflectometric Interference Spectroscopy is based on the Interference of light beams, which are reflected at interfaces with different refractive indices. A thin glass slide, typically coated with an interference layer of 330nm SiO2, is illuminated with white light. At each interface the lightbeam is partly reflected. As the reflected beams travel different optical paths, a phase difference is introduced. Any change of optical thickness (n*d) will lead to changes in the interference spectrum.

Therefore, if the surface is made biologically active so that one may 'trap' compounds of interest, monitoring optical thickness changes reveals binding events. Binding curves are typically ecorded as the apparent optical thickness (nd) of the interference layer vs time. RIfS systems provide measurement of real time kinetics of bioanalyte binding to a surface immobilized sensor molecule. RIfS allows monitoring of Protein-Protein-Interaction, DNA-Protein-Binding, even SNPs Single Nucleotide Polymirphism) are detected.

RIfS has also been shown to the detection of volatile organic compounds (VOCs) and other environmental relevant analytes by enrichment of these species in polymers. Also the polymers can be modified to size selectivity or polarisation selectivity.