Giant light-harvesting nanoantenna for single-molecule detection in ambient light

Here, we explore the enhancement of single-molecule emission by a polymeric nanoantenna that can harvest energy from thousands of donor dyes to a single acceptor. In this nanoantenna, the cationic dyes are brought together, in very close proximity, using bulky counterions, thus enabling ultrafast diffusion of excitation energy (≤30 fs) with minimal losses. Our 60 nm nanoparticles containing >10,000 rhodamine-based donor dyes can efficiently transfer energy to 1–2 acceptors, resulting in an antenna effect of ~1,000. Therefore, single Cy5-based acceptors become 25-fold brighter than quantum dots QD655. This unprecedented amplification of the acceptor dye emission enables observation of single molecules at illumination powers (1–10 mW cm−2) that are >10,000-fold lower than typically required in single-molecule measurements. Finally, using a basic set-up, which includes a ×20 air objective and a scalable complementary metal-oxide–semiconductor camera, we could detect single Cy5 molecules by simply shining divergent light on the sample at powers equivalent to sunlight.