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Funding Information: Funding from the Jane and Aatos Erkko Foundation (J.J.T. and A.K./M.V.-R.) and the Academy of Finland (#330584 and #350797 J.J.T./#308992 A.K. and A.K.N./#330896 M.V.-R.) is gratefully acknowledged. The authors also acknowledge the provision of facilities and technical support by Aalto University at OtaNano - Nanomicroscopy Center (Aalto-NMC). Publisher Copyright: © 2023 The Royal Society of Chemistry. Hierarchical self-assembly of nanostructures with addressable complexity has been a promising route for realizing novel functional materials. Traditionally, the fabrication of such structures on a large scale has been achievable using top-down methods but with the cost of complexity of the fabrication equipment versus resolution and limitation mainly to 2D structures. More recently bottom-up methods using molecules like DNA have gained attention due to the advantages of low fabrication costs, high resolution and simplicity in an extension of the methods to the third dimension. One of the more promising bottom-up techniques is DNA origami due to the robust self-assembly of arbitrarily shaped nanostructures with feature sizes down to a few nanometers. Here, we show that under specific ionic conditions of the buffer, the employed plus-shaped, blunt-ended Seeman tile (ST) origami forms elongated, ordered 2D lattices, which are further rolled into 3D tubes in solution. Imaging structures on a surface by atomic force microscopy reveals ribbon-like structures, with single or double layers of the origami lattice. Further studies of the double-layered structures in a liquid state by confocal microscopy and cryo-TEM revealed elongated tube structures with a relatively uniform width but with a varying length. Through meticulous study, we concluded that the assembly process of these 3D DNA origami tubes is heavily dependent on the concentration of both mono- and divalent cations. In particular, nickel seems to act as a trigger for the formation of the tubular assemblies in liquid.

International audience; Hybrid nanostructures, in which a known number of quantum emitters are strongly coupled to a plasmonic resonator, should feature optical properties at room temperature such as few-photon nonlinearities or coherent superradiant emission. We demonstrate here that this coupling regime can only be reached with dimers of gold nanoparticles in stringent experimental conditions, when the interparticle spacing falls below 2 nm. Using a short transverse DNA double-strand, we introduce 5 dye molecules in the gap between two 40 nm gold particles and actively decrease its length down to sub-2 nm values by screening electrostatic repulsion between the particles at high ionic strengths. Single-nanostructure scattering spectroscopy then evidences the observation of a strong-coupling regime in excellent agreement with electrodynamic simulations. Furthermore, we highlight the influence of the planar facets of polycrystalline gold nanoparticles on the probability of observing strongly coupled hybrid nanostructures.

Nano-antennas represent a modern approach to enhance the detection of quantum emitters, but they often require sophisticated nanofabrication techniques and great control over the antenna-emitter distance in three dimensions. Recently, we demonstrated that planar antennas can beam light into a narrow cone, hence providing a large collection efficiency even for low numerical-aperture (NA) optics [1] , [2] . Planar antennas operate like optical Yagi-Uda antennas, where the reflector element is a flat mirror and the director element is a thin metal film. Therefore, they are easier to fabricate and require position control in only one dimension.

Fluorescence detection is a well-established method for spectroscopy and sensing. However, since dye molecules are dipolar light sources, a large fraction of the emitted photons can be lost. An effective approach to overcome this problem relies on a planar antenna configuration, which beams the radiation pattern of the dye into a narrow cone. A planar antenna works like a Yagi-Uda antenna, but reflector and director elements are made of thin metal films. Here, by introducing a scanning optical fiber, which incorporates the reflector or the director, we demonstrate a tunable planar antenna for spectroscopic and sensing applications. Our results show that the radiation pattern narrows down to 26 degrees (FWHM), which implies a high collection efficiency by low-NA optics.

An effective approach to improve the detection efficiency of nanoscale light sources relies on a planar antenna configuration, which beams the emitted light into a narrow cone. Planar antennas operate like optical Yagi-Uda antennas, where reflector and director elements are made of metal films. Here we introduce and investigate, both theoretically and experimentally, a scanning implementation of a planar antenna. Using a small ensemble of molecules contained in fluorescent nanobeads placed in the antenna, we independently address the intensity, radiation pattern, and decay rate as a function of distance between a flat-tip scanning gold wire (reflector) and a thin gold film coated on a glass coverslip (director). The scanning planar antenna changes the radiation pattern of a single fluorescent bead, and it beams light into a narrow cone down to angles of 45 ∘ (full width at half maximum). Moreover, the collected signal compared to the case of a glass coverslip is larger than a factor of three, which is mainly due to the excitation enhancement. These results offer a better understanding of the modification of light–matter interaction by planar antennas, and they hold promise for applications such as sensing, imaging, and diagnostics.

We provide some text that was inadvertently omitted from our article [J. Opt. Soc. Am. B 38, 2528 (2021)JOBPDE0740-322410.1364/JOSAB.434980].

Author(s): Markesevic, N; Oemrawsingh, SSR; Schultz, D; Gwinn, EG; Bouwmeester, D | Abstract: Polarization-resolved excitation and emission measurements on individual 10-15 atom silver clusters formed on DNA are presented. The emission is highly linearly polarized, typically around 90% for all emitters, whereas the polarization dependence of the excitation strongly varies from emitter to emitter. These observations support the hypothesis that the luminescence arises from collective electron oscillations along rod-shaped silver clusters, whereas the excitation process does not necessarily have a strong preferential polarization direction and thus may involve energy and/or charge transfer between the cluster and DNA. In addition to stabilizing the clusters, the DNA also appears to strongly influence the available paths for excitation. © 2014 WILEY-VCH Verlag GmbH a Co. KGaA, Weinheim.

We develop approaches to hold fluorescent silver clusters composed of only 10-20 atoms in nanoscale proximity, while retaining the individual structure of each cluster. This is accomplished using DNA clamp assemblies that incorporate a 10 atom silver cluster and a 15 or 16 atom silver cluster. Thermally modulated fluorescence resonance energy transfer (FRET) verifies assembly formation. Comparison to Förster theory, using measured spectral overlaps, indicates that the DNA clamps hold clusters within roughly 5 to 6 nm separations, in the range of the finest resolutions achievable on DNA scaffolds. The absence of spectral shifts in dual-cluster FRET pairs, relative to the individual clusters, shows that select few-atom silver clusters of different sizes are sufficiently stable to retain structural integrity within a single nanoscale DNA construct. The spectral stability of the cluster persists in a FRET pair with an organic dye molecule, in contrast to the blue-shifted emission of the dye.

We report on the first single emitter fluorescence spectra of DNA-stabilized silver clusters (Ag:DNAs) at ambient and cryogenic temperatures. While Ag:DNAs have received much attention recently due to their sequence-tunable emission wavelengths, the nature of the optical transitions (molecule-like or collective, cluster-like) is an open question. By removing the ensemble broadening present in previous spectroscopic studies, we probe the line widths Γ and brightness of individual Ag:DNA emitters. A roughly 5-fold increase in brightness from 295 to 1.7 K is accompanied by a factor of 2 decrease in Γ. The symmetric emission line shape, its insensitivity to embedding medium, and the independence of emission wavelength on excitation energy together indicate that the measured Γ represents the homogeneous line width, while the large, ∼100 meV values of Γ suggest rapid dephasing of a collective excited state of the silver cluster.

Owing to their low glass transition temperature, T-g, amorphous thin films of N,N'-bis(3-methylphenyl)-N,N'bis(phenyl)benzidine (TPD) undergo morphological changes even at room temperature. It has been noticed previously that exposure to UV light can increase apparent T-g of TPD films and thus stabilize their morphology. However, the reason behind increase in structural stability was not examined at the time. Here we present evidence that TPD molecules undergo photo-oxidation in air when exposed to lambda approximate to 350 nm radiation and that less than 5% of the photo-oxidized species are needed to prevent dewetting of thin TPD films. We propose that photo-oxidized TPD species bind strongly to both ordinary TPD molecules and to terminal hydroxyl groups at the substrate surface, which decreases mobility of TPD molecules and makes thin TPD film less prone to morphology changes. (C) 2014 Elsevier B.V. All rights reserved.

Fluorescent DNA-stabilized silver nanoclusters contain both cationic and neutral silver atoms. The absorbance spectra of compositionally pure solutions follow the trend expected for rod-shaped silver clusters, consistent with the polarized emission measured from individual nanoclusters. The data suggest a rod-like assembly of silver atoms, with silver cations mediating attachment to the bases.