Surface Plasmon Resonance Sensors for Biomolecular Chirality

A chiral object, i.e., one that is distinguishable from its mirror image, interacts differently with photons of left-hand (+) and right-hand (-) circular polarizations. The difference in the absorption part is known as circular dichroism ( CD), which is usually observed for biomolecules with one or more chiral centers and is widely used to probe their molecular stereometry. Such probing has an increasingly broad importance for biomedical and pharmacological fields due to synthesis/separation/detection of homochiral species, biological role of chiral organization, and structural response to environmental conditions and enantiomeric drugs. Recent theoretical and experimental works demonstrated that the CD signal from chiral organic molecules could appear in the plasmonic band when they are coupled with plasmonic particles. Here report an intriguing case in which non-chiral plasmonic nanoparticles are surrounded by a monolayer of DNA molecules that have chirality arising from its helix structure and individual nucleobases. We identify gold/silver core/shell nanocubes as most effective by providing a giant, 2 orders of magnitude CD enhancement in a near-visible region, while DNA's native CD signal appears at much higher energy. The discovered phenomenon opens novel opportunities in ultrasensitive probing of biomolecules and for novel optical nanomaterials based on the chiral elements.