Nano-Fanowmen: Fano-Resonant Plasmonic Nanoparticles

Fano resonance stands as a significant driving force in the advancement of cutting-edge sensors, ultrasensitive spectroscopy, and microdevices with superior optical properties1–9. Although Fano resonant structures have been extensively studied within the resolution range achievable by state-of-the-art photolithography techniques (tens of nm), exploring Fano resonance at the nanoscale—where strong quantum confinement prevails—remains a challenge. Here, we report colloidal Fano-resonant snowman nanoparticles (nano-Fanowman) in the liquid phase, exhibiting a clear characteristic Fano dip in the ensemble spectrum. We demonstrate precise tuning of an 80-nm nano-Fanowman structure featuring a secondary ~1-nm intragap through a DNA-nanointerfacial modulation strategy. Probed using dyes located within this intragap, these nanoparticles exhibited a surface-enhanced Raman scattering (SERS) signal approximately 100-fold stronger than that of non-Fano-resonant counterparts, owing to efficient energy transfer from a bright mode to a dark mode. Enabled by the Fano resonance effect, detectable SERS signals were achievable at laser powers as low as ~1 nW.