Apparatus and methods for detecting molecules are disclosed. One such embodiment is an apparatus for detecting molecules. The apparatus includes a substrate having a surface; and an array of features formed over the surface in a grating pattern. Each of the features includes a top surface. The apparatus also includes a plurality of receptors coupled to the top surfaces of the features. Each of the receptors is configured to bind to a target molecule. A sample is provided over the substrate while a light is illuminated onto the apparatus. A light scattered by the apparatus is detected by a spectrometer. The presence and/or concentration of target molecules can be determined, based at least partly on a shift in the spectral peak of the light.