Talk by Guillermo P. Acuna

Abstract

Metallic nanoantennas based on gold and silver have long enabled nanoscale control of light. Yet, their operation is fundamentally constrained by high ohmic losses in the visible regime and limited spectral operation. In this presentation, we introduce a comprehensive nanophotonic framework that moves beyond noble‑metal plasmonics, combining colloidal high‑index dielectric silicon nanoparticles (SiNPs), deep‑UV plasmonic rhodium nanocubes, and universal DNA‑origami–based assembly into a single coherent platform.

High‑index dielectrics such as silicon support both electric and magnetic dipolar Mie resonances—the magnetic mode arising from circular displacement currents inside the particle. These magnetic resonances can be tuned to occur in the visible range and are essential for tailoring scattering phase and amplitude. Using DNA origami to position individual fluorophores at distances of 7–80 nm from crystalline SiNPs, we experimentally demonstrated broadband lifetime reduction dominated by enhanced radiative decay, while the non‑radiative rate remains nearly unchanged, even at 7 nm separation. This confirms the predicted low‑loss, non‑quenching nature of dielectric nanoantennas compared to gold, where non‑radiative channels dominate at the short range [1].

The presence of both electric and magnetic modes enables interference effects absent in plasmonic particles. In a second study, we exploited these resonances to realize directional emission, beam steering, and color routing from a single spherical SiNP. DNA‑origami placement of single emitters at well‑defined positions allowed us to map far‑field patterns and observe forward–backward asymmetries consistent with Kerker‑type interference conditions, where constructive interference of the electric and magnetic dipoles suppresses backward scattering or forward scattering depending on wavelength and geometry. We obtained forward‑to‑backward ratios up to ~7 dB and demonstrated that lateral displacement of the emitter rotates the emission lobe—realizing single‑molecule beam steering. Larger SiNPs exhibit wavelength‑dependent reversal of the emission direction, enabling single‑particle color routing in the visible regime [2]. 

These dielectric and hybrid architectures are enabled by a universal DNA functionalization method. Traditional thiol chemistry is excellent for Au and Ag, but not applicable to many alternative materials. We developed a freezing‑assisted SPAAC click‑chemistry protocol that achieves dense DNA grafting (up to ~0.2 molecules nm⁻²) onto silicon, silica, polymers, core–shell particles, and metals such as rhodium. This process drastically increases reaction efficiency, improves colloidal stability, and enables robust DNA‑origami–guided assembly across material classes. We further used this method to assemble SiNP monomers and dimers with >50% yield, validating deterministic stoichiometric incorporation [3]. 

Finally, we expand into the deep‑UV, where noble metals fail to support stable plasmons. By removing PVP ligands and functionalizing rhodium nanocubes with DNA, we assembled 10 nm‑gap UV‑plasmonic dimers on DNA origami with a yield of ~69%. A single streptavidin protein placed inside the nanogap exhibits up to 22× autofluorescence enhancement, a 6.6× reduction in fluorescence lifetime, and a >10× increase in photon budget, enabling label‑free single‑protein spectroscopy based on intrinsic tryptophan/tyrosine emission. Numerical simulations confirm that the enhancement arises from strong UV field confinement and Purcell‑enhanced decay in the nanogap [4]. 

 

References

[1] Siegel, N.; Sanz-Paz, M.; González-Colsa, J.; Serrera, G.; Zhu, F.; Szalai, A. M.; Kołątaj, K.; Fujii, M.; Sugimoto, H.; Albella, P.; et al. Distance-Dependent Interaction between a Single Emitter and a Single Dielectric Nanoparticle Using DNA Origami. Small Struct. 2025, 6 (11), 2500299.

[2]  Sanz-Paz, M.; Siegel, N.; Serrera, G.; González-Colsa, J.; Zhu, F.; Kołątaj, K.; Fujii, M.; Sugimoto, H.; Albella, P.; Acuna, G. P. Color Routing and Beam Steering of Single-Molecule Emission with a Spherical Silicon Nanoantenna. Adv. Funct. Mater. 2026, e29955.

[3]  Siegel, N.; Hasebe, H.; Chiarelli, G.; Garoli, D.; Sugimoto, H.; Fujii, M.; Acuna, G. P.; Kołątaj, K. Universal Click-Chemistry Approach for the DNA Functionalization of Nanoparticles. J. Am. Chem. Soc. 2024, 146, 17250–17260.

[4] Corduri, N.; Veedu, M. K.; Yu, Y.; Zou, Y.; Liu, J.; Garoli, D.; Acuna, G. P.; Wenger, J.; Kołątaj, K. DNA-Origami-Assembled Rhodium Nanoantennas for Deep-UV Label-Free Single-Protein Detection. Adv. Funct. Mater. 2026, e32006.

 

About the speaker

Guillermo P. Acuna
Department of Physics, University of Fribourg (Switzerland)