DNA-assembled bimetallic plasmonic nanosensors

Plasmonic hybrid nanomaterials are highly desirable in advanced sensing applications. Different components in these materials undertake distinct roles and work collectively. One material component may act as an efficient light concentrator and optical probe, whereas another provides specific chemical or biological functionality. In this work, we present DNA-assembled bimetallic plasmonic nanostructures and demonstrate their application for the all-optical detection of hydrogen. Gold (Au) nanorods are functionalized with DNA strands, which serve both as linkers and seeding sites for the growth of palladium (Pd) nanocrystals and facilitate reliable positioning of Pd satellites around an Au nanorod at an ultrashort spacing in the nanometer range. Dark-field scattering spectra of single Au-DNA-Pd nanorods were recorded during controlled cycles of hydrogen gas exposure, and an unambiguous concentration-dependent optical response was observed. Our method enables, for the first time, the all-optical detection of hydrogen-induced phase-change processes in sub-5-nm Pd nanocrystals at the single-antenna level. By substituting the Pd satellites with other functional materials, our sensor platform can be extended to plasmonic sensing of a multitude of chemical and biological reagents, both in liquid and gaseous phases.