Deterministic assembly of single optical cavity formed by gold dimensional DNA origami

Controllable strong interactions between a nanocavity and a single emitter is important to manipulating optical emission in a nanophotonic system but challenging to achieve.Herein a three-dimensional DNA origami,named as DNA rack(DR)is proposed and demonstrated to deterministically and precisely assemble single emitters within ultra-small plasmonic nanocavities formed by closely coupled gold nanorods(AuNRs).Uniquely,the DR is in a saddle shape,with two tubular grooves that geometrically allow a snug fit and linearly align two AuNRs with a bending angle <10°.It also includes a spacer at the saddle point to maintain the gap between AuNRs as small as 2-3 nm,forming a nanocavity estimated to be 20 nm^(3) and an experimentally measured O factor of 7.3.A DNA docking strand is designed at the spacer to position a single fluorescent emitter at nanometer accuracy within the cavity.Using Cy5 as a model emitter,a -30-fold fluorescence enhancement and a significantly reduced emission lifetime(from 1.6 ns to 670 ps)were experimentally verified,confirming significant emitter-cavity interactions.This DR-templated assembly method is capable of fitting AuNRs of variable length-to-width aspect ratios to form anisotropic nanocavities and deterministically incorporate different single emitters,thus enabling flexible design of both cavity resonance and emission wavelengths to tailor light-matter interactions at nanometer scale.