Large-area films of vertically-aligned semiconductor nanorods have the potential to be useful, active materials for optoelectronic devices. We demonstrate here a highly facile thermal annealing approach for reversibly assembling 28 nm long CdSe nanorods into vertically aligned arrays in solution. Using temperature to control solvent strength, aggregated nanorods in a marginally poor solvent mixture were first dispersed at elevated temperatures and then reassembled into freely suspended, ordered sheets of aligned nanorods up to 24 μm in diameter upon slow cooling. The assembly method was tolerant of nanorod polydispersity and was effective over a wide range of solvents and nanorod concentrations. The pre-assembled nanorods could be directly drop-cast from solution onto a substrate and rapidly dried to obtain a film of vertically aligned nanorods.

The development of strategies to couple biomolecules covalently to surfaces is necessary for constructing sensing arrays for biological and biomedical applications. One attractive conjugation reaction is hydrazone formation--the reaction of a hydrazine with an aldehyde or ketone--as both hydrazines and aldehydes/ketones are largely bioorthogonal, which makes this particular reaction suitable for conjugating biomolecules to a variety of substrates. We show that the mild reaction conditions afforded by hydrazone conjugation enable the conjugation of DNA and proteins to the substrate surface in significantly higher yields than can be achieved with traditional bioconjugation techniques, such as maleimide chemistry. Next, we designed and synthesized a photocaged aryl ketone that can be conjugated to a surface and photochemically activated to provide a suitable partner for subsequent hydrazone formation between the surface-anchored ketone and DNA- or protein-hydrazines. Finally, we exploit the latent functionality of the photocaged ketone and pattern multiple biomolecules on the same substrate, effectively demonstrating a strategy for designing substrates with well-defined domains of different biomolecules. We expect that this approach can be extended to the production of multiplexed assays by using an appropriate mask with sequential photoexposure and biomolecule conjugation steps.

The effect of cetyl-trimethylammonium bromide (CTAB) on enhancing the fluorescence resonance energy transfer (FRET) between two dye-conjugated DNA strands was studied using fluorescence emission spectroscopy and dynamic light scattering (DLS). For hybridized DNA where one strand is conjugated with a TAMRA donor and the other with a TexasRed acceptor, increasing the concentration of CTAB changes the fluorescence emission properties and improves the FRET transfer efficiency through changes in the polarity of the solvent, neutralization of the DNA backbone and micelle formation. For the DNA FRET system without CTAB, the DNA hybridization leads to contact quenching between TAMRA donor and TexasRed acceptor producing reduced donor emission and only a small increase in acceptor emission. At 50 µM CTAB, however, the sheathing and neutralization of the dye-conjugated dsDNA structure significantly reduces quenching by DNA bases and dye interactions, producing a large increase in FRET efficiency, which is almost four fold higher than without CTAB.

Using an aqueous single reactor arc discharge process with oil-in-water emulsions allows production of 2D multilayered graphenes (MLGs and 3D graphene-based crumpled/sphere-like particles with low levels of defects). The confinement forces to create 3D particles from 2D MLGs are estimated to be 2.5 μN for crumpled particles and 70 μN for spherical hollow particles.

Dimerization and resultant quenching of donor and acceptor dyes conjugated on DNA causes loss of fluorescent resonant energy transfer (FRET) efficiency. However, when complexed with surfactants and divalent metal ions, sheathing effects insulate and shield the DNA structures, reducing dimerization and quenching which leads to significant enhancement of FRET efficiency.