  The theory to calculate circular dichroism (CD) of chiral molecules in a
finite cluster with arbitrarily disposed objects has been developed by means of
T-matrix method. The interactions between chiral molecules and nanostructures
have been investigated. Our studies focus on the case of chiral molecules
inserted into plasmonic hot spots of nanostructures. Our results show that the
total CD of the system with two chiral molecules is not sum for two cases when
two chiral molecules inserted respectively into the hot spots of nanoparticle
clusters as the distances among nanoparticles are small, although the
relationship is established at the case of large interparticle distances. The
plasmonic CD arising from structure chirality of nanocomposites depends
strongly on the relative positions and orientations of nanospheroids, and are
much greater than that from molecule-induced chirality. However, the
molecule-induced plasmonic CD effect from the molecule-NP nanocomposites with
special chiral structures can be spectrally distinguishable from the structure
chirality-based optical activity. Our results provide a new theoretical
framework for understanding the two different aspects of plasmonic CD effect in
molecule-NP nanocomposites, which would be helpful for the experimental design
of novel biosensors to realize ultrasensitive probe of chiral information of
molecules by plasmon-based nanotechnology.
