In this paper we have proposed and analyzed a novel integrated optic racetrack resonator based biosensor. The device is capable of distinguishing compressive and tensile stresses on a cantilever due to conformational changes of protein.We have considered Bovine Serum Albumin (BSA) and Immunoglobulin G (IgG). The change of surface stress upon adsorption of IgG is compressive and of BSA is tensile. When the biomolecules adhere to the device surface, due to photo elastic effect the effective refractive index and length of racetrack resonator change. Our simulation results show that the resonant wavelength shifts by 0.3196X 10 -3 nm/ με which is a measure of surface stress.