The present invention provides an optical assay apparatus that includes a light source module and an optical sensor. The light source module produces light having a range of propagation angles. The sensor includes a light adjusting portion and an assay sensing portion. The light adjusting portion receives the light produced by the light source module and provides light having a propagation angle that is substantially constant to the assay sensing portion. In one embodiment, the sensor may be coupled with the light source module by an interrogation module which includes a window in which a waveguide is integrated. In another embodiment, the sensor and interrogation module are mounted in an automated assay platform that provides two-dimensional or three-dimensional movement of the sensor so that it can be sequentially immersed in solutions required to perform a particular assay protocol. While the sensor is immersed in a particular liquid, the system provides oscillatory movement of the sensor and/or rotary movement of the contacted liquid to increase evanescent wave region reaction rates with targeted analytes and/or reagents.