  Here we demonstrate a new concept for designing an ultra-sensitive deformed
cavity biosensor. Owning to the breaking of rotational symmetry, the field
distribution is not uniform along the cavity boundary and results in the
dependence of spectra shift and mode splitting on the position of a scatter. In
this case, the deformed cavity sensor can be extremely sensitive to the
location of particle binding on the cavity boundary. Moreover, the directional
emission from the deformed microcavity provides a possibility to detect a
single particle or molecule in the far field.
