By the modification of the biosensor applying a new illumination method comprising a beam expander, a two-cell liquid crystal modulator and by using optimized sensor chips with an extra outcoupling grating, Patko et al. have improved the resolution of grating coupled interferometer. In two-channel measurements, the refractive index changes of the ambient could be followed with a detection limit of 9×10 −8 and the changes of surface mass density could be detected with a resolution of 0.05 pg/mm 2 ( Patko et al., 2012 ).