Electrogenerated chemiluminescence of iridium-containing ROMP block copolymer and self-assembled micelles

The electrochemical properties and electrogenerated chemiluminescence (ECL) of an Ir(ppy)2(bpy)(+)-containing ROMP monomer, block copolymer (containing Ir(ppy)2(bpy)(+) complexes, PEG chains, and butyl moieties), and self-assembled micelles were investigated. Following polymerization of the iridium complex, we observed multiple oxidation peaks for the block copolymer in cyclic voltammograms (CV) and differential pulse voltammograms (DPV), suggesting the presence of multiple environments for the iridium complexes along the polymer backbone. The ECL signals from monomer 1 and polymer 2 were reproducible over continuous CV cycles and stable over prolonged potential biases, demonstrating their robustness toward ECL-based detection. Comparison of the ECL signal of the block copolymer, containing multiple iridium complexes attached to the backbone, and the monomeric complex showed enhanced signals for the polymer. In fact, formation and reopening of the self-assembled micelles allowed recovery of the polymer and near complete retention of its original ECL intensity.

Simple design for DNA nanotubes from a minimal set of unmodified strands: rapid, room-temperature assembly and readily tunable structure

DNA nanotubes have great potential as nanoscale scaffolds for the organization of materials and the templation of nanowires and as drug delivery vehicles. Current methods for making DNA nanotubes either rely on a tile-based step-growth polymerization mechanism or use a large number of component strands and long annealing times. Step-growth polymerization gives little control over length, is sensitive to stoichiometry, and is slow to generate long products. Here, we present a design strategy for DNA nanotubes that uses an alternative, more controlled growth mechanism, while using just five unmodified component strands and a long enzymatically produced backbone. These tubes form rapidly at room temperature and have numerous, orthogonal sites available for the programmable incorporation of arrays of cargo along their length. As a proof-of-concept, cyanine dyes were organized into two distinct patterns by inclusion into these DNA nanotubes.

Luminescent Iridium(III)-Containing Block Copolymers: Self-Assembly into Biotin-Labeled Micelles for Biodetection Assays

Luminescent polymers containing Ir(ppy)₂(bpy) PF₆ complexes, biocompatible poly(ethylene glycol) (PEG) chains, and biotin moieties were synthesized via ring-opening metathesis polymerization (ROMP). Their self-assembly in water into micelles resulted in an increased quantum yield compared to open polymer chains in acetonitrile, which is likely due to core rigidity and desolvation. Streptavidin coated magnetic beads were employed to analyze the binding ability of these micelles. The positioning of the molecular recognition moiety biotin within the polymer chain had a very significant effect on the availability of biotin on the micelle surface and the ability of the micelles to bind to streptavidin. Simply attaching biotin to the end of the ROMP polymer yielded micelles in which the biotin units were shielded by the PEG chains, whereas the synthesis of a new ROMP monomer containing biotin at the end of the PEG chains resulted in improved surface availability of the biotin group. Preliminary experiments in which streptavidin was microcontact-printed onto functionalized glass coverslips also indicated specific binding between the micelles and streptavidin and further demonstrated the potential of these micelle systems to function as luminescent probes in solid-phase biodetection assays.

Rolling circle amplification-templated DNA nanotubes show increased stability and cell penetration ability

DNA nanotubes hold promise as scaffolds for protein organization, as templates of nanowires and photonic systems, and as drug delivery vehicles. We present a new DNA-economic strategy for the construction of DNA nanotubes with a backbone produced by rolling circle amplification (RCA), which results in increased stability and templated length. These nanotubes are more resistant to nuclease degradation, capable of entering human cervical cancer (HeLa) cells with significantly increased uptake over double-stranded DNA, and are amenable to encapsulation and release behavior. As such, they represent a potentially unique platform for the development of cell probes, drug delivery, and imaging tools.

A facile, modular and high yield method to assemble three-dimensional DNA structures

We describe a rapid and quantitative method to generate DNA cages of deliberately designed geometry from readily available starting strands. Balancing the incorporation of sequence uniqueness and symmetry in a face-centered approach to 3D construction can result in triangular (TP), rectangular (RP), and pentagonal prisms (PP) without compromising the potential for nanostructure addressability.

Self-assembly of metal-DNA triangles and DNA nanotubes with synthetic junctions

The site-specific insertion of organic and inorganic molecules into DNA nanostructures can provide unique structural and functional capabilities. We have demonstrated the inclusion of two types of molecules. The first is a diphenylphenanthroline (dpp, 1) molecule that is site specifically inserted into DNA strands and which can be used as a template to create metal-coordinating pockets. These building blocks can then be used to assemble metal-DNA 2D and 3D structures, including metal-DNA triangles, described here. The second insertion is a triaryl molecule that provides geometric control in the preparation of 2D single-stranded DNA templates. These can be designed to further assemble into geometrically well-defined nanotubes. Here, we detail the steps involved in the construction of metal-DNA triangles and DNA nanotubes using these methods.

Self-assembly of three-dimensional DNA nanostructures and potential biological applications

A current challenge in nanoscience is to achieve controlled organization in three-dimensions, to provide tools for biophysics, molecular sensors, enzymatic cascades, drug delivery, tissue engineering, and device fabrication. DNA displays some of the most predictable and programmable interactions of any molecule, natural or synthetic. As a result, 3D-DNA nanostructures have emerged as promising tools for biology and materials science. In this review, strategies for 3D-DNA assembly are discussed. DNA cages, nanotubes, dendritic networks, and crystals are formed, with deliberate variation of their size, shape, persistence length, and porosities. They can exhibit dynamic character, allowing their selective switching with external stimuli. They can encapsulate and position materials into arbitrarily designed patterns, and show promise for numerous biological and materials applications.