We present an optical resonance sensor capable of measurement of refractive index in highly nonhomogeneous materials. Traditional optical resonance sensors fail when the size of particles is comparable with the wavelength (100 nm and larger). Our new nanoengineered design allows incorporation of a highly delocalized mode into a resonance structure. The sensing depth of the device was measured to be 1 mum, the largest reported in the literature as far as we know, with a quality factor of 500. We demonstrate two applications.