Plasmonic coupling and long-range transfer of an excitation along a DNA nanowire

Spatial Separation of Plasmonic Hot-Electron Generation and a Hydrodehalogenation Reaction Center Using a DNA Wire

Using hot charge carriers far from a plasmonic nanoparticle surface is very attractive for many applications in catalysis and nanomedicine and will lead to a better understanding of plasmon-induced processes, such as hot-charge-carrier- or heat-driven chemical reactions. Herein we show that DNA is able to transfer hot electrons generated by a silver nanoparticle over several nanometers to drive a chemical reaction in a molecule nonadsorbed on the surface. For this we use 8-bromo-adenosine introduced in different positions within a double-stranded DNA oligonucleotide. The DNA is also used to assemble the nanoparticles into nanoparticles ensembles enabling the use of surface-enhanced Raman scattering to track the decomposition reaction. To prove the DNA-mediated transfer, the probe molecule was insulated from the source of charge carriers, which hindered the reaction. The results indicate that DNA can be used to study the transfer of hot electrons and the mechanisms of advanced plasmonic catalysts.

Fabrication of micro-patterned substrates for plasmonic sensing by piezo-dispensing of colloidal nanoparticles

In this work we describe a very fast and flexible method for fabrication of plasmon-supporting substrates with micro-patterning capability, which is optimized for plasmonic sensing. We combined a wet chemistry approach to synthesize metallic nanoparticles with a piezo-dispensing system enabling deposition of nanoparticles on the substrates with micrometer precision. In this way, an arbitrary pattern consisting of 200 μm small spots containing plasmonic nanostructures can be produced. Patterns with various nanoparticles exhibiting different plasmonic properties were combined, and the surface density of the particles could be easily varied via their solution concentrations. We showed that under controlled conditions the dispensing process caused no aggregation of the particles and it enabled full transfer of the colloidal solutions onto the substrate. This is an important condition, which enables these substrates to be used for reliable plasmonic sensing based on monitoring the spectral shift of the nanoparticles. We demonstrated the functionality of such substrates by detection of small protein adsorption on the spots based on plasmon label-free sensing method.

AFM-Based Probing of the Flexibility and Surface Attachment of Immobilized DNA Origami

The flexible and precise immobilization of self-organizing DNA nanostructures represents a key step in the integration of DNA-based material for potential electronic or sensor applications. However, the involved processes have still not been well studied and are not yet fully understood. Thus, we investigated the potential for the mechanical manipulation of DNA origami by atomic force microscopy (AFM) in order to study the interaction between intramolecular flexibility and surface-attachment forces. AFM is particularly suitable for nanoscale manipulation. Previous studies showed the potential for pushing, bending, and cutting double-stranded DNA (dsDNA) with an AFM tip. Understanding the involved parameters may enable control over different processes such as nanointegration, precise cutting, and stretching of preassembled DNA origami. We demonstrate the defined manipulation and flexibility of DNA origami immobilized on mica in the nanometer range: controlled cutting, folding, and stretching as a function of the magnesium concentration.

DNA as UV light-harvesting antenna

The ordered structure of UV chromophores in DNA resembles photosynthetic light-harvesting complexes in which quantum coherence effects play a major role in highly efficient directional energy transfer. The possible role of coherent excitons in energy transport in DNA remains debated. Meanwhile, energy transport properties are greatly important for understanding the mechanisms of photochemical reactions in cellular DNA and for DNA-based artificial nanostructures. Here, we studied energy transfer in DNA complexes formed with silver nanoclusters and with intercalating dye (acridine orange). Steady-state fluorescence measurements with two DNA templates (15-mer DNA duplex and calf thymus DNA) showed that excitation energy can be transferred to the clusters from 21 and 28 nucleobases, respectively. This differed from the DNA-acridine orange complex for which energy transfer took place from four neighboring bases only. Fluorescence up-conversion measurements showed that the energy transfer took place within 100 fs. The efficient energy transport in the Ag-DNA complexes suggests an excitonic mechanism for the transfer, such that the excitation is delocalized over at least four and seven stacked bases, respectively, in one strand of the duplexes stabilizing the clusters. This result demonstrates that the exciton delocalization length in some DNA structures may not be limited to just two bases.

DNA-Assembled Advanced Plasmonic Architectures

The interaction between light and matter can be controlled efficiently by structuring materials at a length scale shorter than the wavelength of interest. With the goal to build optical devices that operate at the nanoscale, plasmonics has established itself as a discipline, where near-field effects of electromagnetic waves created in the vicinity of metallic surfaces can give rise to a variety of novel phenomena and fascinating applications. As research on plasmonics has emerged from the optics and solid-state communities, most laboratories employ top-down lithography to implement their nanophotonic designs. In this review, we discuss the recent, successful efforts of employing self-assembled DNA nanostructures as scaffolds for creating advanced plasmonic architectures. DNA self-assembly exploits the base-pairing specificity of nucleic acid sequences and allows for the nanometer-precise organization of organic molecules but also for the arrangement of inorganic particles in space. Bottom-up self-assembly thus bypasses many of the limitations of conventional fabrication methods. As a consequence, powerful tools such as DNA origami have pushed the boundaries of nanophotonics and new ways of thinking about plasmonic designs are on the rise.

Hybrid Structures for Surface-Enhanced Raman Scattering: DNA Origami/Gold Nanoparticle Dimer/Graphene

A combination of three innovative materials within one hybrid structure to explore the synergistic interaction of their individual properties is presented. The unique electronic, mechanical, and thermal properties of graphene are combined with the plasmonic properties of gold nanoparticle (AuNP) dimers, which are assembled using DNA origami nanostructures. This novel hybrid structure is characterized by means of correlated atomic force microscopy and surface-enhanced Raman scattering (SERS). It is demonstrated that strong interactions between graphene and AuNPs result in superior SERS performance of the hybrid structure compared to their individual components. This is particularly evident in efficient fluorescence quenching, reduced background, and a decrease of the photobleaching rate up to one order of magnitude. The versatility of DNA origami structures to serve as interface for complex and precise arrangements of nanoparticles and other functional entities provides the basis to further exploit the potential of the here presented DNA origami-AuNP dimer-graphene hybrid structures.

Assembling programmable FRET-based photonic networks using designer DNA scaffolds

DNA demonstrates a remarkable capacity for creating designer nanostructures and devices. A growing number of these structures utilize Förster resonance energy transfer (FRET) as part of the device's functionality, readout or characterization, and, as device sophistication increases so do the concomitant FRET requirements. Here we create multi-dye FRET cascades and assess how well DNA can marshal organic dyes into nanoantennae that focus excitonic energy. We evaluate 36 increasingly complex designs including linear, bifurcated, Holliday junction, 8-arm star and dendrimers involving up to five different dyes engaging in four-consecutive FRET steps, while systematically varying fluorophore spacing by Förster distance (R0). Decreasing R0 while augmenting cross-sectional collection area with multiple donors significantly increases terminal exciton delivery efficiency within dendrimers compared with the first linear constructs. Förster modelling confirms that best results are obtained when there are multiple interacting FRET pathways rather than independent channels by which excitons travel from initial donor(s) to final acceptor.

Plasmonically enhanced electron escape from gold nanoparticles and their polarization-dependent excitation transfer along DNA nanowires

Here we show plasmon mediated excitation transfer along DNA nanowires over up to one micrometer. Apparently, an electron excitation is initiated by a femtosecond laser pulse that illuminates gold nanoparticles (AuNP) on double stranded DNA (dsDNA). The dependency of this excitation on laser wavelength and polarization are investigated. Excitation of the plasmon resonance of the AuNPs via one- and two-photon absorption at 520 and 1030 nm, respectively, was explored. We demonstrate an excitation transfer along dsDNA molecules at plasmon supported four-photon excitation of AuNP cluster or at laser field driven nanoparticle electron tunneling for an alignment of the attached dsDNA to the polarization of the electric field of the laser light. These results extend the previously observed plasmonically induced three-photon excitation transfer along DNA nanowires to another nanoparticle material (gold) and the adapted irradiation wavelengths.