Surface-Enhanced Circular Dichroism Spectroscopy on Periodic Dual Nanostructures

Increasing the sensitivity of chiral spectroscopic techniques such as circular dichroism (CD) spectroscopy is a current aspiration in the research field of nanophotonics. Enhancing CD spectroscopy depends upon of two complementary requirements: the enhancement of the electromagnetic fields perceived by the molecules under study and the conservation of the helicity of those fields, guaranteed by duality symmetry. In this work, we introduce a systematic method to design nanostructured dual periodic photonic systems capable of enhancing molecular CD spectroscopy resonantly. As an illustration, we engineer a dual 1D silicon nanoparticle array and show that its collective optical modes can be efficiently employed to resonantly enhance by two orders of magnitude the local density of optical chirality and, thus, the CD signal obtained from a given molecular sample on its vicinity.