The present invention provides a sensor having, one or more optical slab waveguides having one or more target regions. The target regions may interact with gas molecules or trap, entrain or capture one or more targets of interest. The optical slab waveguides are adapted to receive one or more input optical beams from one or more light sources to create a plurality of propagating optical waves in optical slab waveguide. The propagating optical waves interact with said one or more target regions to create an optical output wavefront that may be in the form of a diffraction pattern. The target regions may be functionalized with an antibody, polymer, cell, tissue, or biological material.