Hierarchical assembly of metal nanoparticles, quantum dots and organic dyes using DNA origami scaffolds.

The self-assembly of nanoscale elements into three-dimensional structures with precise shapes and sizes is important in fields such as nanophotonics, metamaterials and biotechnology. Short molecular linkers have previously been used to create assemblies of nanoparticles, but the approach is limited to small interparticle distances, typically less than 10 nm. Alternatively, DNA origami can precisely organize nanoscale objects over much larger length scales. Here we show that rigid DNA origami scaffolds can be used to assemble metal nanoparticles, quantum dots and organic dyes into hierarchical nanoclusters that have a planet-satellite-type structure. The nanoclusters have a tunable stoichiometry, defined distances of 5-200 nm between components, and controllable overall sizes of up to 500 nm. We also show that the nanoscale components can be positioned along the radial DNA spacers of the nanostructures, which allows short- and long-range interactions between nanoparticles and dyes to be studied in solution. The approach could, in the future, be used to construct efficient energy funnels, complex plasmonic architectures, and porous, nanoengineered scaffolds for catalysis.

Two-color laser printing of individual gold nanorods.

We report on the deposition of individual gold nanorods from an optical trap using two different laser wavelengths. Laser light, not being resonant to the plasmon resonances of the nanorods, is used for stable trapping and in situ alignment of individual nanorods. Laser light, being resonant to the transversal mode of the nanorods, is used for depositing nanorods at desired locations. The power and polarization dependence of the process is investigated and discussed in terms of force balances between gradient and scattering forces, plasmonic heating, and rotational diffusion of the nanorods. This two-color approach enables faster printing than its one-color equivalent and provides control over the angular orientation (±16°) and location of the deposited nanorods at the single-nanorod level.

Design and optical trapping of a biocompatible propeller-like nanoscale hybrid.

Designing nanoscale objects with the potential to perform externally controlled motion in biological environments is one of the most sought-after objectives in nanotechnology. Different types of chemically and physically powered motors have been prepared at the macro- and microscale. However, the preparation of nanoscale objects with a complex morphology, and the potential for light-driven motion has remained elusive to date. Here, we go a step forward by designing a nanoscale hybrid with a propeller-resembling shape, which can be controlled by focused light under biological conditions. Our hybrid, hereafter "Au@DNA-origami", consists of a spherical gold nanoparticle with self-assembled, biocompatible, two-dimensional (2D) DNA sheets on its surface. As a first step toward the potential utilization of these nanoscale objects as light-driven assemblies in biological environments, we show that they can be optically trapped, and hence translated and deposited on-demand, and that under realistic trapping conditions the thermally induced dehybridization of the DNA sheets can be avoided.

Patterning of pH sensitive fluorescent bipyridazine derivatives.

A pH sensitive pipeprazine substituted bipyridazine fluorophore, DPP-BPDZ was explored as a pH sensor in solution and thin film state. Greenish highly fluorescent solution of the DPP-BPDZ with fluorescence quantum yield of 0.63 showed fluorescence decrease as the acetic acid concentration of the media was increased. The fluorescence quenching was correlated linearly with the content of acetic acid dose and attributed to the protonation at the terminal piperazine group. An acid sensitive film was fabricated using a transparent polymeric host (PMMA) and the DPP-BPDZ dye molecules as a guest. The resultant bright green fluorescent film (1.4 microm thick) showed exponential decrease of the fluorescence intensity as the pH of the dipping solution was decreased. In the range of pH below 4.5, the film sensitivity to pH was higher than the pH range over 4.5. A patternable film sensor was fabricated by introducing a photo acid generator (PAG) layer on the dye layer. Fluorescence patterns was formed on the film sensor through a photo-mask by relatively weak power of UV light (0.4 mW/cm2). Fluorescent line patterns having 10 microm line width were obtained with high fluorescence contrast between the patterns.

Rodlike fluorescent pi-conjugated 3,3'-bipyridazine ligand: optical, electronic, and complexation properties.

We report on the design and synthesis of a new quadrupolar pi-conjugated 3,3'-bipyridazine D-A-D ligand. Its electronic and optical properties were investigated. Besides high fluorescence and pronounced solvatochromism, it exhibits an inherent electroactivity exploited to build an organic green light emitting device. Moreover, the ability of this ligand to complex metallic centers (Cu(I), Ni(II), Pt(II), and Ir(III)) was also investigated to access different geometries and to tune their electronic and optical properties. These preliminary results open up the synthesis of heavy-metal complexes to obtain phosphorescent emitters.

Solvatochromic fluorescence of piperazine-modified bipyridazines for an organic solvent-sensitive film.

Bipyridazines were modified with heterocyclic amines such as piperazine to give symmetric quadrupolar (SPBP) and asymmetric dipolar (APBP) bipyridazine. The fluorescence of SPBP and APBP was highly sensitive to solvent polarity, giving a synthetic rainbow of emission in different organic solvents. The solvent-induced changes in the Stokes shift of the bipyridazines resulted in positive solvatochromism. The symmetric bipyridazine showed higher solvatochromic sensitivity than that of the asymmetric bipyridazine and diazines. The positive solvatochromic fluorescence properties were reproduced in a binary system of toluene/dimethyl sulfoxide (DMSO) mixture, which showed a synthetic rainbow of emission by varying the DMSO content in toluene. An organic sensitive poly(methyl methacrylate) film containing SPBP exhibited a visible sensitivity for the detection of solvents by their polarity upon exposure to organic solvent molecules.

Fluorescent grating patterns of photopolymer film containing ethylene glycol phenyl ether acrylate.

Photopolymer films containing photoreactive monomers in the presence of fluorescent polyanthracene were investigated for fluorescent grating pattern formation using a 3D holographic method. A monofunctional acrylate, ethylene glycol phenyl ether acrylate (PA), was used as the core monomer for the formation of the polymerization induced grating pattern. Photopolymer films were prepared from a mixture of PA and polyanthracene with a binder polymer and a photo radical initiator. The film's thickness was adjusted by the solution's composition to optimize grating pattern efficiency (>90%). The diffraction efficiency was increased in the presence of polyanthracene. Furthermore, the fluorescence intensity was more enhanced after grating formation. A vivid fluorescent gap electrode pattern with fine gratings was patterned, providing a new method for patterning organic thin films with distinct read-out processes.