Diffraction gratings comprising a substrate with protrusions extending therefrom. In one embodiment, the protrusions are made of a porous material, for example porous silicon with a porosity of greater than about 10%. The diffraction grating may also be constructed from multiple layers of porous material, for example porous silicon with a porosity of greater than about 10%, with protrusion of attached thereto. In some embodiments the protrusions may be made from photoresist or another polymeric material. The gratings are the basis for sensitive sensors. In some embodiments, the sensors are functionalized with selective binding species, to produce sensors that specifically bind to target molecules, for example chemical or biological species of interest.