Plasmonic Nano-bolas Hunt DNA Targets

We present the design principles and assembly route for a reconfigurable DNA-scaffolded nanomachine comprising a fluorophore and two gold nanoparticles (AuNPs) operated by DNA strand displacement. The mechanism confines the fluorophore in the proximity of one or simultaneously two DNA-tethered 15 nm AuNPs, resulting in discrete emission levels associated with the system state. Bi- and single-molecule DNA scaffolds were compared as alternative building blocks, aiming at the optimal structure in terms of reversibility, response to molecular triggers, and signal-to-noise ratio. Upon comparison, single-molecule DNA scaffold (i.e., nano-bolas), devoid of intrastructural equilibria, was only minimally affected by cross-talk interferences and stood out for its highly reversible transitions, lower noise, and better kinetics. Distance-dependent responses and kinetics were fully in harmony with theoretical modeling, well illustrating the nano-bolas interconversion between a linear and a quasi-ring geometry. The nano-bolas actuator could find application as an ultrasensitive, reversible, and small-volume plasmonic reporter for single-strand nucleic acid analytes.