A multi-grating resonant waveguide (RWG) biosensor for an optical reader system having a spatial resolution limit is disclosed. The multi-grating RWG biosensor includes one or more signal-grating regions and one or more reference-grating regions. The multi-grating RWG biosensor can also include a non-resonance region that spatially separates the one or more signal-grating regions, that spatially separates the one or more reference-grating regions, and that spatially separates the one or more reference-grating regions from the one or more signal-grating regions. The non-resonance region can have a minimum width greater than the optical reader system spatial resolution limit. The RWG biosensor can have an asymmetric split-grating configuration. Methods of measuring a signal resonant wavelength of a multi-grating RWG biosensor using an optical reader having a spatial resolution limit are also disclosed.