Scheme of a focal molography chip: laser light is coupled onto a thin-film waveguide, thereby illuminating a “mologram”—an assembly of receptor molecules in a spatially ordered pattern. The mologram diffracts light coherently, focusing it onto an Airy disk on the detector. When receptor molecules bind specifically with an analyte of interest, their interaction results in index-of-refraction changes that can alter the detected signal. Nonbiospecific bindings are not arranged in the same order as the receptors and would thus not create a coherent diffraction signal. The diameter of the mologram that is exposed to the sample is about 0.4 mm, corresponding to about 109 coherently assembled receptor molecules.