A biosensor substrate structure is provided that eliminates the effects of optical interference of light reflected from a substrate/air interface with light reflected by the biosensor's active surface by incorporating a roughened or "non-specular" surface on the lower surface of the substrate opposite the grating. One can generate a useful non-specular or "anti-interference" surface in a number of ways in accordance with this disclosure, including (1) by adding a coating of optically diffuse material, such as UV cured acrylate, to the sensor substrate, (2) etching or otherwise roughening the surface of the sensor substrate, or (3) applying a grating structure to the surface.