Simulations Show a Hexatic Phase in Porous Media
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approaches are used, based on the formation of the metal NPs in the DNA-NP conjugate. In this research, the ex situ method was employed because the researchers discovered that negatively charged THPAuNPs can bind densely to the negatively charged calf thymus DNA. During the metallization procedure, DNA was first immobilized on a silicon substrate by O2 plasma treatment to enhance immobilization and spin-coating to elongate the molecules. Before the THP-AuNP sol was applied to the substrate, the particles were precipitated in ethanol, then dissolved in an ethanol–water solution. Optimum results with respect to density of particle templating, avoidance of excess particles on the substrate, and lack of defects in the resultant wires were obtained at an ethanol:water ratio of 95:5. After rinsing and drying, the samples were treated with an electroless gold plating solution in order to form conductive nanowires for further characterization. Atomic force microscopy revealed that after calf thymus DNA molecules on a silicon substrate were treated with THP-AuNPs in 95% ethanol, the DNA molecules were decorated with particles, with some excess particles (0.7 nm to 2 nm in size) also on the substrate. Scanning electron microscopy images showed that the electroless gold plating of the resulting DNAAuNP conjugates provides nanowires ~30–40 nm in width and longer than 2 µm. The good contrast against the silicon surface indicates high conductivity and the metallization was restricted almost entirely to the DNA. The results of the electrical transport capabilities of the DNA nanowires showed that their electrical conductivities were about one-thousandth that of bulk gold. To determine what kind of mechanism controls the binding between THP-AuNPs and DNA, several hypotheses were considered, based on the interactions between THP-AuNPs and DNA, such as adsorption of THP-AuNPs to hydrophilic DNA molecules on the silicon oxide surface, hydrogen-bonding interactions in between, ligand replacement by groups on DNA that can coordinate to the AuNP surface, and the covalent bonding between THP and amino groups of the DNA base. The process can be finished in ~10 min, but the in situ approaches that employ metal salts or complexes as precursors take longer than 1 h. The technique reported here by O. Harnack and coworkers could be used for future electronic circuits because it can lower the fabrication cost and is suitable for feature sizes below the current limit of optical lithography. However, issues about the binding mechanism between the 736
THP-AuNPs and DNA, and how the solvent and substrate influence the process, need to be further studied. YUE HU
Direct Ink-Jet Printing Assembles ZrO2 Powder into 3D Shape Three-dimensional shapes can be created from ceramic powders by forcing droplets of “ink” containing the powder through an ink-jet nozzle, layering the deposition to generate height. Xinglong Zhao and colleagues from the University of London in conjunction with Jin-Hua Song from Brunel University report their work on the creation
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