Competition of chiroptical effect caused by nanostructure and chiral molecules

The theory of calculating circular dichroism (CD) of chiral molecules in a finite cluster with arbitrarily disposed objects has been developed by means of a 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 the sum for two cases when two chiral molecules inserted separately into the hot spots of nanoparticle (NP) clusters when the distances between nanoparticles are small, although the relationship is established in 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 is 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 distinguished 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 probing of chiral information on molecules by plasmon-based nanotechnology.