The present invention is directed to an optical grating sensor configured to detect a phase change in light passing though the system due to a binding event caused by an analyte. The grating sensor may include a light source that may be, for example, a coherent light source. The invention may also include a first diffraction grating having a first period. A micro-electrical mechanical system (MEMS) may be displaced from the first diffraction grating and may be configured to modulate the light received form the coherent light source. An analyte recognition material may be disposed on the surface of the first grating. A detector may be configured to receive light form the coherent light source after the light has been diffracted from the first diffraction grating and modulated by the MEMS. In another embodiment of the present invention, the grating sensor may be configured to operate in two modes. The first mode may be a mode the detect a phase change in the light due to a binding event. The second mode may include the detection of fluorescence due to a binding event and may employ tagging of the analytes.