  We report a theoretical study of clusters of evanescently-coupled 2D
whispering-gallery (WG) mode optical micro-cavities (termed "photonic
molecules") as chemosensing and biosensing platforms. Photonic molecules (PMs)
supporting modes with narrow linewidths, wide mode spacing, and greatly
enhanced sensitivity to the changes in the dielectric constant of their
environment and to the presence of individual sub-wavelength sized
nanoparticles in the PM evanescent-field region are numerically designed. This
type of optical biosensor can be fabricated in a variety of material platforms
and integrated on a single chip that makes it a promising candidate for a small
and robust lab-on-a-chip device. Possible applications of the developed
methodology and the designed PM structures to the near-field microscopy, single
nano-emitter microcavity lasing, and cavity-controlled single-molecule
fluorescence enhancement are also discussed.
