Optical waveguide lightmode spectroscopy (OWLS) is a device that relies on a thin-film optical waveguide, enclosing a discrete number of guided electromagnetic waves. Guidance is achieved by means of a grating coupler. It is based on the measurements of effective refractive index of a thin-film layer above the waveguide. This technique works only on highly transparent surfaces.
Other methods widely used for measuring the amount of protein adsorbed on surfaces include radio-labelling, Lowry assay, scanning angle reflectometry, total internal reflection fluorescence, bicinchoninic acid assay etc.