Nanocage-Confined Synthesis of Fluorescent Polycyclic Aromatic Hydrocarbons in Zeolite.

Polycyclic aromatic hydrocarbons (PAHs) attract much attention for applications to organic light-emitting diodes, field-effect transistors, and photovoltaic cells. The current synthetic approaches to PAHs involve high-temperature flash pyrolysis or complicated step-by-step organic reactions, which lead to low yields of PAHs. Herein, we report a facile and scalable synthesis of PAHs, which is carried out simply by flowing acetylene gas into zeolite under mild heating, typically at 400 °C and generates the products of 0.30 g g-1 zeolite. PAHs are synthesized via acetylene polymerization inside Ca2+-ion-exchanged Linde type A (LTA) zeolite, of which the α-cage puts a limit on the product molecular size as a confined-space nanoreactor. The resultant product after the removal of the zeolite framework exhibits brilliant white fluorescence emission in N-methylpyrrolidone solution. The product is separated into four different color emitters (violet, blue, green, and orange) by column chromatography. Detailed characterizations of the products by means of various spectroscopic methods and mainly mass spectrometric analyses indicate that coronene (C24H12) is the main component of the blue emitter, while the green emitter is a mixture of planar and curved PAHs. The orange can be attributed to curved PAHs larger than ovalene, and the violet to smaller molecules than coronene. The PAH growth mechanism inside Ca2+-exchanged LTA zeolite is proposed on the basis of mass spectral analyses and density functional theory calculations.

High-speed, high-purity separation of gold nanoparticle-DNA origami constructs using centrifugation.

DNA origami is a powerful platform for assembling gold nanoparticle constructs, an important class of nanostructure with numerous applications. Such constructs are assembled by the association of complementary DNA oligomers. These association reactions have yields of <100%, requiring the development of methods to purify the desired product. We study the performance of centrifugation as a separation approach by combining optical and hydrodynamic measurements and computations. We demonstrate that bench-top microcentrifugation is a simple and efficient method of separating the reaction products, readily achieving purities of >90%. The gold nanoparticles play a number of critical roles in our system, functioning not only as integral components of the purified products, but also as hydrodynamic separators and optical indicators of the reaction products during the purification process. We find that separation resolution is ultimately limited by the polydispersity in the mass of the gold nanoparticles and by structural distortions of DNA origami induced by the gold nanoparticles. Our study establishes a methodology for determining the design rules for nanomanufacturing DNA origami-nanoparticle constructs.

Electrodeposited reduced graphene oxide-PEDOT:PSS/Nafion hybrid interface for the simultaneous determination of dopamine and serotonin.

The electrochemically deposited reduced graphene oxide-PEDOT:PSS/Nafion (rGO-PP/NF) hybrid material has provided a favorable interface for the simultaneous detection of dopamine (DA) and serotonin (5-HT). The rGO-PP/NF onto the Au seed layer of the flexible substrate was simple, and it was followed by the sequential electrophoretic deposition of GO, reduction at the optimal pH buffer media, electropolymerization of EDOT:PSS, and Nafion coating. The strong electron-transport capacity between rGO-PEDOT:PSS and the negatively charged Nafion matrix might allow the highly sensitive, simultaneous, and selective detection of DA and 5-HT due to its high affinity for cations. In the results of the electrochemical response, well-separated oxidation peaks were observed in a mixture that contained various concentrations of DA and 5-HT. It showed the dynamic sensing of DA and 5-HT in the ranges of 0.5-75 µM and 0.05-50 µM, respectively, and the detection limits of 0.17 and 0.16 µM, respectively. In the mixture of DA and 5-HT, the sensor had a detection limit of 0.1 µM for 5-HT and DA, and its sensitivities of DA and 5-HT were 99.3 and 86 µA/µMcm2. Furthermore, it demonstrated high selectivity, reproducibility, stability, and a recovery property in the human serum spike test that was good enough for the practical use.

Flexible sensor with electrophoretic polymerized graphene oxide/PEDOT:PSS composite for voltammetric determination of dopamine concentration.

We demonstrate a novel, flexible sensor with graphene oxide/PEDOT:PSS (GO/PEDOT:PSS) composite for voltammetric determination of selective low levels of dopamine. The well-distributed GO and EDOT:PSS suspension in water were deposited simply and polymerized. Consequently, the EDOT:PSS provided a strong interaction between GO and PEDOT:PSS, and it also had well-tailored interfacial properties that allowed the highly selective and sensitive determination of DA. Since the interfacial net charge is well-constructed, the sensor satisfies both the requirements of selectivity and the highly sensitive detection of low amounts of DA. In the results, the sensor with the GO/PEDOT:PSS composite exhibited a low interfacial impedance of about 281.46 ± 30.95 Ω at 100 Hz and a high charge storage capacity (53.94 ± 1.08 µC/cm2) for the detection of dopamine. In addition, the interference from ascorbic acid was reduced effectively to a minimum by electrostatic charge repelling of the AA and the distinct difference for the oxidation peak of the UA. Due to the fact that the GO/PEDOT:PSS composite had a net negative charge and, enhanced interfacial properties, the sensor showed a dopamine detection limit of 0.008 µM and a sensitivity of 69.3 µA/µMcm2.

Highly dispersed Pt nanoclusters supported on zeolite-templated carbon for the oxygen reduction reaction.

The formation of highly dispersed Pt nanoclusters supported on zeolite-templated carbon (PtNC/ZTC) by a facile electrochemical method as an electrocatalyst for the oxygen reduction reaction (ORR) is reported. The uniform micropores of ZTC serve as nanocages to stabilize the PtNCs with a sharp size distribution of 0.8-1.5 nm. The resultant PtNC/ZTC exhibits excellent catalytic activity for the ORR due to the small size of the Pt clusters and high accessibility of the active sites through the abundant micropores in ZTC.

Symmetry controls the face geometry of DNA polyhedra.

Two complementary strategies have been developed to control the face geometry during the self-assembly of DNA polyhedra from branched DNA nanomotifs (tiles). In these approaches, any two interacting tiles are not equivalent in terms of either sequence or orientation; thus, each face must contain an even number of tiles. As a demonstration, DNA cubes, whose each face contains four tiles, have been assembled through these approaches.

Reversible switching of pRNA activity on the DNA packaging motor of bacteriophage phi29.

This paper reports a reversible switching of the biological activity of an RNA molecule, packaging RNA (pRNA), which is a central component of the DNA packaging motor of bacteriophage phi29. The switching mechanism contains two components: (1) inhibition of pRNA by a short antisense DNA (asDNA) that can bind to the 3' end of the pRNA and inactivate the packaging motor; and (2) reactivation of pRNA by isothermal removal of asDNA from pRNA through a strand displacement strategy. The switching process can be repeated for multiple cycles and has been demonstrated by gel electrophoresis and a virion assembly assay.

DNA-based nanofabrications.

Beyond its biological importance, short DNA sequences are of increasing interest as excellent and versatile building blocks, in material science and nanotechnology. DNA nanotechnology has been rapidly developed and has branched into several significantly different directions. Controlling DNA nanostructures is one of the most important branches, in which well-defined static nanostructures are constructed from rationally designed DNA motifs. The diversity and complexity of such DNA nanostructures also endow them with promising applications in nanofabrications, nanoelectronics, biodiagnostics, and DNA computations. In this review, we will summarize our recent efforts in this direction.

Large-scale fabrication of commercially available, nonpolar linear polymer film with a highly ordered honeycomb pattern.

Highly ordered, hexagonally patterned poly(methyl methacrylate) (PMMA) thin film is successfully fabricated using an improved phase separation method. A mixture of chloroform and methanol, which is used as a volatile solvent/nonsolvent pair, effectively controls the surface morphology and sensitively determines the ordered pattern. In particular, the methanol accumulation, which induces the formation of a gel-like protective layer and enhances the lateral capillary force, is crucial in the formation of the highly ordered hexagonal pattern even when using a nonpolar polymer such as PMMA. The convergence of cost-effective and large-scale production of highly ordered micropatterned film has wide potential for application, and it can enable new prospects for the commercialization of future high-tech devices that require specific multifunctionality.

Super-amphiphilic surface of nano silica/polyurethane hybrid coated PET film via a plasma treatment.

This study first reports the fabrication of a super-amphiphilic surface using PET films with a silica-polyurethane hybrid top-coat layer through a non-thermal, one-atmospheric-pressure plasma treatment. This surface displays contact angle close to zero with both aqueous and oily liquids, which has attracted enormous attention for a wide-range of practical applications. We systematically investigated the influence of the plasma treatment time on the wetting behavior of the silica-polyurethane coated PET surface. The changes in morphology and chemical composition of PET surfaces before and after a plasma treatment were analyzed. In order to gain an insight into the formation of a super-amphiphilic PET surface and optimize the conditions under which super-amphiphilicity can be realized, we used a hemi-wicking action as a theoretical model and experimentally verified it through determining the critical angle. We also proposed a guide for designing a nano-sphere patterned PDMS surface which can generate super-wetting properties after a plasma treatment.

A surfactant-free bio-compatible film with a highly ordered honeycomb pattern fabricated via an improved phase separation method.

Thin films of bio-compatible poly(lactic acid) with highly ordered hexagonal patterns were successfully fabricated under normal ambient conditions without using any surfactant via an improved phase separation method. The patterned surface was successfully applied to fabricate silicon/copper dome-patterned electrodes for high-performance hybrid capacitors.

RNA-DNA hybrid origami: folding of a long RNA single strand into complex nanostructures using short DNA helper strands.

Quick folding of a long RNA strand using short DNA staple strands (at a 1 : 1 ratio) into various pre-designed nanostructures in high yields has been demonstrated.

Quantum dot-DNA origami binding: a single particle, 3D, real-time tracking study.

The binding process of quantum dots and DNA origami was monitored using a 3D, real-time, single-particle tracking system. Single-molecule binding events were directly observed and precise measurements of the diffusion coefficient and second-order photon correlation function, g(2)(τ), were combined to distinguish free quantum dots from different conjugates of nQdot-origami.

Synergistic self-assembly of RNA and DNA molecules.

DNA has recently been used as a programmable 'smart' building block for the assembly of a wide range of nanostructures. It remains difficult, however, to construct DNA assemblies that are also functional. Incorporating RNA is a promising strategy to circumvent this issue as RNA is structurally related to DNA but exhibits rich chemical, structural and functional diversities. However, only a few examples of rationally designed RNA structures have been reported. Herein, we describe a simple, general strategy for the de novo design of nanostructures in which the self-assembly of RNA strands is programmed by DNA strands. To demonstrate the versatility of this approach, we have designed and constructed three different RNA-DNA hybrid branched nanomotifs (tiles), which readily assemble into one-dimensional nanofibres, extended two-dimensional arrays and a discrete three-dimensional object. The current strategy could enable the integration of the precise programmability of DNA with the rich functionality of RNA.

DNA self-assembly: from 2D to 3D.

This paper describes our recent efforts on the self-assembly of three-dimensional (3D) DNA nanostructures from DNA star motifs (tiles). DNA star motifs are a family of DNA nanostructures with 3, 4, 5, or 6 branches; they are named as 3-, 4-, 5-, 6-point-star motifs, respectively. Such motifs are programmed to further assemble into nanocages (regular polyhedra or irregular nanocapsules) with diameters ranging from 20 nm to 2 microm. Among them, DNA nanocages derived from 3-point-star motif consists of a group of regular polyhedra: tetrahedra, hexahedra (or cubes), dodecahedra and buckyballs (containing 4, 8, 20, and 60 units of the 3-point-star motif, respectively). An icosahedron consists of twelve 5-point-star motifs and is similar to the shapes of spherical viruses. 6-point-star motifs can not assemble into regular polyhedra; instead, some sphere-like or irregular cages with diameters about 1-2 microm will form. Similar large cages can also assemble from the 5-point-star motif when the DNA concentrations are higher than those for assembling regular icosahedra. In our study, we have identified several important factors for assembly of well-defined 3D nanostructures, including the concentration, the flexibility, and the arm length of the DNA tiles and the association strength between the DNA tiles.