We study the reflection of a tightly focused Gaussian beam off a near symmetric resonant tunneling structure comprising two identical coupled waveguides. The coupled waveguides are loaded on each side by a spacer layer and a high index prism. Reflection of a Gaussian beam from such a resonant structure is associated with beam distortion and even beam splitting. We start with the distortion of the beam profile for a symmetric structure as a function of various parameters of the system. The broken spatial symmetry is introduced through the reference channel on one side and the sample channel on the other side as spacer layers. We monitor the dip in the beam profile when the two channels are filled with the sample and the reference liquid. We show that presence and absence of hemoglobin and its oxygenation states can be quantified by looking at the beam profile dip. Our results may find applications in high resolution sensing.