Nanoscale plasmonics for molecular recognition and light-triggered molecular release

Metallic nanostructures designed to provide plasmon resonances at specific optical frequencies and strong yet uniform near-field electromagnetic enhancements are useful nanodevices for light-driven sensing and actuation. To use plasmonic nanostructures for molecular recognition, their properties must be exploited in combination with molecular layers that provide an optical signature that corresponds to capture of a target molecule. DNA oligomers bound to the surface of plasmonic nanostructures provide an optical signal that is sensitive to the conformational changes in the DNA itself due to interaction with other molecules, as would occur in binding events. This type of optical detection is label-free and reporter-free, that is, it does not depend upon the presence of a dye molecule bound to the DNA to provide an optical signal. DNA-drug interactions can be directly detected in this manner: the binding kinetics of chemotherapy drugs such as cisplatin can be directly monitored by this method, providing a streamlined spectroscopic approach to drug discovery. Combining this DNA-based sensing strategy with plasmonic nanostructures allows us to optically detect specific target molecules depending only on the conformation dependence of the DNA SERS signal itself. This strategy allows us to detect specific proteins in the nanomolar range, but also, in small molecule detection, to discriminate between binding to specific target molecules and nonspecific binding events that occur with similar molecules.