Molecularly Addressable Nanoparticle-on-Mirror Cavity Arrays via DNA Origami-Mediated Template Assembly

Nanoparticle-on-mirror (NPoM) cavities confine light within molecular gaps, but conventional drop casting does not register cavities at predefined coordinates. We integrate electron-beam lithography, face-selective DNA origami placement, and DNA-mediated gold-nanosphere docking to position molecularly programmable NPoMs on flat gold mirrors. Across six patches containing 2538 sites in total, the estimated mean single-particle occupation was approximately 84.7%. Dark-field spectra of cavities programmed with cyanine 5 (Cy5) show a split response centered near the Cy5 transition. Comparison with bare-cavity sweeps of facet width, gap thickness, and spacer index supports a molecularly anchored, Rabi-like interpretation of this response within a damped coupled-oscillator model. Photoluminescence controls reveal substantial gold luminescence, so dark-field scattering is used as the primary coupling observable. The platform therefore combines deterministic cavity registration with sequence-programmable molecular optical functionality.