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1.
J Phys Chem Lett ; 10(10): 2386-2392, 2019 May 16.
Artigo em Inglês | MEDLINE | ID: mdl-31010285

RESUMO

Molecular excitons are used in a variety of applications including light harvesting, optoelectronics, and nanoscale computing. Controlled aggregation via covalent attachment of dyes to DNA templates is a promising aggregate assembly technique that enables the design of extended dye networks. However, there are few studies of exciton dynamics in DNA-templated dye aggregates. We report time-resolved excited-state dynamics measurements of two cyanine-based dye aggregates, a J-like dimer and an H-like tetramer, formed through DNA-templating of covalently attached dyes. Time-resolved fluorescence and transient absorption indicate that nonradiative decay, in the form of internal conversion, dominates the aggregate ground state recovery dynamics, with singlet exciton lifetimes on the order of tens of picoseconds for the aggregates versus nanoseconds for the monomer. These results highlight the importance of circumventing nonradiative decay pathways in the future design of DNA-templated dye aggregates.


Assuntos
Carbocianinas/química , DNA/química , Corantes Fluorescentes/química , Espectrometria de Fluorescência , Fatores de Tempo
2.
ACS Nano ; 13(3): 2986-2994, 2019 03 26.
Artigo em Inglês | MEDLINE | ID: mdl-30758934

RESUMO

The excitonic circuitry found in photosynthetic organisms suggests an alternative to electronic circuits, but the assembly of optically active molecules to fabricate even simple excitonic devices has been hampered by the limited availability of suitable molecular scale assembly technologies. Here we have designed and operated a hybrid all-optical excitonic switch comprised of donor/acceptor chromophores and photochromic nucleotide modulators assembled with nanometer scale precision using DNA nanotechnology. The all-optical excitonic switch was operated successfully in both liquid and solid phases, exhibiting high ON/OFF switching contrast with no apparent cyclic fatigue through nearly 200 cycles. These findings, combined with the switch's small footprint and volume, estimated low energy requirement, and potential ability to switch at speeds in the 10s of picoseconds, establish a prospective pathway forward for all-optical excitonic circuits.

3.
J Phys Chem A ; 122(46): 8989-8997, 2018 Nov 21.
Artigo em Inglês | MEDLINE | ID: mdl-30380862

RESUMO

The excited state properties of cyanine dyes and the orientations of their aggregates were studied using density functional theory (DFT). The effects of exchange-correlation functional and solvent model on the absorption spectrum of Cy5 was investigated. Using the 6-31+G(d,p) basis set and B3LYP exchange-correlation functional with IEF-PCM (water) solvent, the predicted spectrum achieved a maximum absorbance within 0.007 eV of experiment. An in-house program based on the theoretical model of Kühn, Renger, and May (KRM), which predicts the orientation of dyes within an aggregate from its absorbance and circular dichroism (CD) spectra or vice versa, was used to investigate the orientation of an experimentally observed dimer. The absorbance spectrum predicted using the KRM model of the dimer structure optimized with the 6-31+G(d,p) basis set, ωB97XD exchange-correlation functional, and IEF-PCM solvent agrees with experimental data.

4.
J Phys Chem A ; 122(8): 2086-2095, 2018 Mar 01.
Artigo em Inglês | MEDLINE | ID: mdl-29420037

RESUMO

Exciton delocalization in dye aggregate systems is a phenomenon that is revealed by spectral features, such as Davydov splitting, J- and H-aggregate behavior, and fluorescence suppression. Using DNA as an architectural template to assemble dye aggregates enables specific control of the aggregate size and dye type, proximal and precise positioning of the dyes within the aggregates, and a method for constructing large, modular two- and three-dimensional arrays. Here, we report on dye aggregates, organized via an immobile Holliday junction DNA template, that exhibit large Davydov splitting of the absorbance spectrum (125 nm, 397.5 meV), J- and H-aggregate behavior, and near-complete suppression of the fluorescence emission (∼97.6% suppression). Because of the unique optical properties of the aggregates, we have demonstrated that our dye aggregate system is a viable candidate as a sensitive absorbance and fluorescence optical reporter. DNA-templated aggregates exhibiting exciton delocalization may find application in optical detection and imaging, light-harvesting, photovoltaics, optical information processing, and quantum computing.


Assuntos
Carbocianinas/química , DNA Cruciforme/química , Fluorescência , Corantes Fluorescentes/química , Modelos Moleculares , Moldes Genéticos
5.
J Phys Chem A ; 121(37): 6905-6916, 2017 Sep 21.
Artigo em Inglês | MEDLINE | ID: mdl-28813152

RESUMO

Coherent exciton delocalization in dye aggregate systems gives rise to a variety of intriguing optical phenomena, including J- and H-aggregate behavior and Davydov splitting. Systems that exhibit coherent exciton delocalization at room temperature are of interest for the development of artificial light-harvesting devices, colorimetric detection schemes, and quantum computers. Here, we report on a simple dye system templated by DNA that exhibits tunable optical properties. At low salt and DNA concentrations, a DNA duplex with two internally functionalized Cy5 dyes (i.e., dimer) persists and displays predominantly J-aggregate behavior. Increasing the salt and/or DNA concentrations was found to promote coupling between two of the DNA duplexes via branch migration, thus forming a four-armed junction (i.e., tetramer) with H-aggregate behavior. This H-tetramer aggregate exhibits a surprisingly large Davydov splitting in its absorbance spectrum that produces a visible color change of the solution from cyan to violet and gives clear evidence of coherent exciton delocalization.


Assuntos
Carbocianinas/química , DNA/química , Corantes Fluorescentes/química , Materiais Biomiméticos/química , Materiais Biomiméticos/efeitos da radiação , Carbocianinas/efeitos da radiação , DNA/efeitos da radiação , Transferência de Energia , Corantes Fluorescentes/efeitos da radiação , Cinética , Luz , Cloreto de Magnésio/química , Modelos Químicos , Temperatura , Termodinâmica
6.
Mater Sci Semicond Process ; 38: 278-289, 2015 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-26085801

RESUMO

As an obvious candidate for a p-type dopant in ZnO, nitrogen remains elusive in this role. Nitrogen containing precursors are a potential means to incorporate nitrogen during MOCVD growth. One class of nitrogen-containing precursors are zinc acetate amines, yet, they have received little attention. The synthesis and single crystal X-ray structure of [Zn(acetate)2(en)], and the synthesis of [Zn(acetate)2(en)2], [Zn(acetate)2(benzylamine)2], [Zn(acetate)2(butylamine)2], [Zn(acetate)2(NH3)2], and [Zn(acetate)2(tris)2], where en = ethylenediamine and tris = (tris[hydroxymethyl]aminomethane) are reported. The compounds were characterized by thermogravimetric analysis and pyrolyzed in air and inert gas to yield ZnO. These compounds are useful single source precursors to ZnO bulk powders by alkali precipitation and ZnO thin films by spray pyrolysis. The amine bound to the zinc influences the ZnO crystal size and shape and acts as a nitrogen donor for preparing nitrogen-doped ZnO during alkali precipitation. Thin films of ZnO prepared by spray pyrolysis using the precursors had a (100) preferred orientation and measured n-type to intrinsic conductivity.

7.
Nanoscale ; 7(23): 10382-90, 2015 Jun 21.
Artigo em Inglês | MEDLINE | ID: mdl-25959862

RESUMO

DNA nanotechnology holds the potential for enabling new tools for biomedical engineering, including diagnosis, prognosis, and therapeutics. However, applications for DNA devices are thought to be limited by rapid enzymatic degradation in serum and blood. Here, we demonstrate that a key aspect of DNA nanotechnology-programmable molecular shape-plays a substantial role in device lifetimes. These results establish the ability to operate synthetic DNA devices in the presence of endogenous enzymes and challenge the textbook view of near instantaneous degradation.


Assuntos
Computadores Moleculares , DNA/química , DNA/ultraestrutura , Soro/química , Espectrometria de Fluorescência/métodos , Humanos , Nanotecnologia/métodos , Conformação de Ácido Nucleico
8.
ACS Photonics ; 2(3): 398-404, 2015 Mar 18.
Artigo em Inglês | MEDLINE | ID: mdl-25839049

RESUMO

A promising application of DNA self-assembly is the fabrication of chromophore-based excitonic devices. DNA brick assembly is a compelling method for creating programmable nanobreadboards on which chromophores may be rapidly and easily repositioned to prototype new excitonic devices, optimize device operation, and induce reversible switching. Using DNA nanobreadboards, we have demonstrated each of these functions through the construction and operation of two different excitonic AND logic gates. The modularity and high chromophore density achievable via this brick-based approach provide a viable path toward developing information processing and storage systems.

9.
Nanoscale ; 6(22): 13928-38, 2014 Nov 21.
Artigo em Inglês | MEDLINE | ID: mdl-25311051

RESUMO

High precision, high yield, and high density self-assembly of nanoparticles into arrays is essential for nanophotonics. Spatial deviations as small as a few nanometers can alter the properties of near-field coupled optical nanostructures. Several studies have reported assemblies of few nanoparticle structures with controlled spacing using DNA nanostructures with variable yield. Here, we report multi-tether design strategies and attachment yields for homo- and hetero-nanoparticle arrays templated by DNA origami nanotubes. Nanoparticle attachment yield via DNA hybridization is comparable with streptavidin-biotin binding. Independent of the number of binding sites, >97% site-occupation was achieved with four tethers and 99.2% site-occupation is theoretically possible with five tethers. The interparticle distance was within 2 nm of all design specifications and the nanoparticle spatial deviations decreased with interparticle spacing. Modified geometric, binomial, and trinomial distributions indicate that site-bridging, steric hindrance, and electrostatic repulsion were not dominant barriers to self-assembly and both tethers and binding sites were statistically independent at high particle densities.


Assuntos
DNA/química , Nanopartículas Metálicas/química , Análise em Microsséries/instrumentação , Nanotubos/química , Sítios de Ligação , DNA/metabolismo , Ouro/química , Análise em Microsséries/estatística & dados numéricos , Microscopia de Força Atômica , Microtecnologia/métodos , Nanotecnologia/métodos , Conformação de Ácido Nucleico , Tamanho da Partícula , Probabilidade , Eletricidade Estática , Propriedades de Superfície
10.
Biosens Bioelectron ; 50: 382-6, 2013 Dec 15.
Artigo em Inglês | MEDLINE | ID: mdl-23891867

RESUMO

A catalytic colorimetric detection scheme that incorporates a DNA-based hybridization chain reaction into gold nanoparticles was designed and tested. While direct aggregation forms an inter-particle linkage from only one target DNA strand, catalytic aggregation forms multiple linkages from a single target DNA strand. Gold nanoparticles were functionalized with thiol-modified DNA strands capable of undergoing hybridization chain reactions. The changes in their absorption spectra were measured at different times and target concentrations and compared against direct aggregation. Catalytic aggregation showed a multifold increase in sensitivity at low target concentrations when compared to direct aggregation. Gel electrophoresis was performed to compare DNA hybridization reactions in catalytic and direct aggregation schemes, and the product formation was confirmed in the catalytic aggregation scheme at low levels of target concentrations. The catalytic aggregation scheme also showed high target specificity. This application of a DNA reaction network to gold nanoparticle-based colorimetric detection enables highly-sensitive, field-deployable, colorimetric readout systems capable of detecting a variety of biomolecules.


Assuntos
Técnicas Biossensoriais/métodos , DNA/análise , Ouro/química , Nanopartículas/química , Colorimetria/métodos , Hibridização de Ácido Nucleico/métodos
11.
Nano Lett ; 13(8): 3850-6, 2013 Aug 14.
Artigo em Inglês | MEDLINE | ID: mdl-23841957

RESUMO

DNA origami templated self-assembly has shown its potential in creating rationally designed nanophotonic devices in a parallel and repeatable manner. In this investigation, we employ a multiscaffold DNA origami approach to fabricate linear waveguides of 10 nm diameter gold nanoparticles. This approach provides independent control over nanoparticle separation and spatial arrangement. The waveguides were characterized using atomic force microscopy and far-field polarization spectroscopy. This work provides a path toward large-scale plasmonic circuitry.


Assuntos
DNA/química , Ouro/química , Nanopartículas Metálicas/química , Tamanho da Partícula
12.
Nano Lett ; 12(4): 2117-22, 2012 Apr 11.
Artigo em Inglês | MEDLINE | ID: mdl-22401838

RESUMO

Fluorescence resonance energy transfer (FRET) is a promising means of enabling information processing in nanoscale devices, but dynamic control over exciton pathways is required. Here, we demonstrate the operation of two complementary switches consisting of diffusive FRET transmission lines in which exciton flow is controlled by DNA. Repeatable switching is accomplished by the removal or addition of fluorophores through toehold-mediated strand invasion. In principle, these switches can be networked to implement any Boolean function.


Assuntos
DNA/química , Transferência Ressonante de Energia de Fluorescência
13.
Nano Lett ; 10(9): 3367-72, 2010 Sep 08.
Artigo em Inglês | MEDLINE | ID: mdl-20681601

RESUMO

To fabricate quantum dot arrays with programmable periodicity, functionalized DNA origami nanotubes were developed. Selected DNA staple strands were biotin-labeled to form periodic binding sites for streptavidin-conjugated quantum dots. Successful formation of arrays with periods of 43 and 71 nm demonstrates precise, programmable, large-scale nanoparticle patterning; however, limitations in array periodicity were also observed. Statistical analysis of AFM images revealed evidence for steric hindrance or site bridging that limited the minimum array periodicity.


Assuntos
DNA/química , Nanotubos , Pontos Quânticos , Microscopia de Força Atômica
14.
J Appl Phys ; 107(11): 113501, 2010 Jun 01.
Artigo em Inglês | MEDLINE | ID: mdl-20589105

RESUMO

The magnetomechanical properties of ferromagnetic shape memory alloy Ni-Mn-Ga single crystals depend strongly on the twin microstructure, which can be modified through thermomagnetomechanical training. Atomic force microscopy (AFM) and magnetic force microscopy (MFM) were used to characterize the evolution of twin microstructures during thermomechanical training of a Ni-Mn-Ga single crystal. Experiments were performed in the martensite phase at 25 degrees C and in the austenite phase at 55 degrees C. Two distinct twinning surface reliefs were observed at room temperature. At elevated temperature (55 degrees C), the surface relief of one twinning mode disappeared while the other relief remained unchanged. When cooled back to 25 degrees C, the twin surface relief recovered. The relief persisting at elevated temperature specifies the positions of twin boundaries that were present when the sample was polished prior to surface characterization. AFM and MFM following thermomechanical treatment provide a nondestructive method to identify the crystallographic orientation of each twin and of each twin boundary plane. Temperature dependent AFM and MFM experiments reveal the twinning history thereby establishing the technique as a unique predictive tool for revealing the path of the martensitic and reverse transformations of magnetic shape memory alloys.

15.
J Biomed Mater Res A ; 90(1): 247-55, 2009 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-18496861

RESUMO

Collagen is a major component of the newly synthesized pericellular microenvironment of chondrocytes. Collagen types II, IX, and XI are synthesized and assembled into higher ordered complexes by a mechanism in which type XI collagen plays a role in nucleation of new fibrils, and in limiting fibril diameter. This study utilizes a cell line derived from the Swarm rat chondrosarcoma that allows the accumulation and assembly of pericellular matrix. Immunofluorescence and atomic force microscopy were used to assess early intermediates of fibril formation. Results indicate that this cell line synthesizes and secretes chondrocyte-specific pericellular matrix molecules including types II, IX, and XI collagen and is suitable for the study of newly synthesized collagen matrix under the experimental conditions used. AFM data indicate that small fibrils or assemblies of microfibrils are detectable and may represent precursors of the approximately 20 nm thin fibrils reported in cartilage. Treatment with hyaluronidase indicates that the dimensions of the small fibrils may be dependent upon the presence of hyaluronan within the matrix. This study provides information on the composition and organization of the newly synthesized extracellular matrix that plays a role in establishing the material properties and performance of biological materials such as cartilage.


Assuntos
Condrócitos/metabolismo , Colágeno Tipo II/metabolismo , Colágeno Tipo IX/metabolismo , Colágeno Tipo XI/metabolismo , Matriz Extracelular/metabolismo , Animais , Linhagem Celular Tumoral , Condrócitos/citologia , Colágeno Tipo II/ultraestrutura , Colágeno Tipo IX/ultraestrutura , Colágeno Tipo XI/ultraestrutura , Matriz Extracelular/química , Hialuronoglucosaminidase/metabolismo , Microfibrilas/metabolismo , Microfibrilas/ultraestrutura , Microscopia de Força Atômica , Fenótipo , Ratos
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