Artificial DNA nanostructures 1,2 show promise for the organization of functional materials 3,4 to create nanoelectronic 5 or nano-optical devices. DNA origami, in which a long single strand of DNA is folded into a shape using shorter 'staple strands' 6 , can display 6-nm-resolution patterns of binding sites, in principle allowing complex arrangements of carbon nanotubes, silicon nanowires, or quantum dots. However, DNA origami are synthesized in solution and uncontrolled deposition results in random arrangements; this makes it difficult to measure the properties of attached nanodevices or to integrate them with conventionally fabricated microcircuitry. Here we describe the use of electron-beam lithography and dry oxidative etching to create DNA origami-shaped binding sites on technologically useful materials, such as SiO 2 and diamond-like carbon. In buffer with 100 mM MgCl 2 , DNA origami bind with high selectivity and good orientation: 70-95% of sites have individual origami aligned with an angular dispersion (+ + + + +1 s.d.) as low as + + + + +108 8 8 8 8 (on diamond-like carbon) or + + + + +208 8 8 8 8 (on SiO 2 ).The semiconductor industry is currently faced with the challenges of developing lithographic technology for feature sizes below 22 nm (ref. 7) and exploring new classes of transistors that use carbon nanotubes 8 or silicon nanowires 9 . A major goal of nanotechnology is therefore to couple the self-assembly of molecular nanostructures with conventional microfabrication. A marriage of these so-called bottom-up and top-down fabrication methods would enable us to register individual molecular nanostructures, to electronically address them, and to integrate them into functional devices. One strategy is to use lithography to make templates onto which discrete components can self-assemble. Examples include the assembly of nanoparticles 10,11 , carbon nanotubes 12,13 and nanowires 14 . Lithographic templates can also be used to create hierarchical order: the nanostructures they organize can themselves have internal features with dimensions significantly smaller than those of the original template 15 and can serve as scaffolds for the assembly of still smaller components.Artificial DNA nanostructures are well suited to this approach. They can be synthesized with attachment groups (such as biotin or single-stranded DNA hooks) at defined locations, which can bind objects such as gold nanoparticles 4,16 . Easily designed in arbitrary shapes, DNA origami typically carry 200 such independently addressable sites at a resolution of 6 nm. Figure 1a depicts the self-assembly of triangular DNA origami in solution (see Supplementary Methods 1) and shows an atomic force micrograph (AFM) of their random deposition on mica, a technique ill-suited for integration with microfabrication. Previous lithographically patterned deposition of organic compounds 17 , single-and doublestranded DNA molecules [18][19][20] or DNA nanostructures 21 has achieved highly selective adsorption, but the molecules were smaller than the lith...

The zeta potential of planar sapphire substrates for three different crystallographic orientations was measured by a streaming potential technique in the presence of KCl and (CH3)4NCl electrolytes. The streaming potential was measured for large single crystalline C-plane (0001), A-plane (1120), and R-plane (1102) wafers over a full pH range at three or more ionic strengths ranging from 1 to 100 mM. The roughness of the epi-polished wafers was verified using atomic force microscopy to be on the order of atomic scale, and X-ray photoelectron spectroscopy (XPS) was used to ensure that the samples were free of silica and other contaminants. The results reveal a shift in the isoelectric point (iep) of the three samples by as much as two pH units, with the R-plane surface exhibiting the most acidic behavior and the C-plane samples having the highest iep. The iep at all ionic strengths was tightly centered around a single pH for each wafer. These values of iep are substantially different from the range of pH 8-10 consistently reported in the literature for alpha-Al2O3 particles. Particle zeta potential measurements were performed on a model powder using phase analysis light scattering, and the iep was confirmed to occur at pH 8. Modified Auger parameters (MAP) were calculated from XPS spectra of a monolayer of iridium metal deposited on the sapphire by electron beam deposition. A shift in MAP consistent with the observed differences in iep of the surfaces confirms the effect of surface structure on the transfer of charge between the Ir and sapphire, hence accounting for the changes in acidity as a function of crystallographic orientation.

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An optical tweezers directed parallel DNA oligonucleotide synthesis methodology is described in which controlled pore glass (CPG) beads act as solid substrates in a two-stream microfluidic reactor. The reactor contains two parallel sets of physical confinement features that retain beads in the reagent stream for synthetic reaction but allow the beads to be optically trapped and transferred between the reagent and the inert streams for sequence programming. As a demonstration, we synthesized oligonucleotides of target sequence 25-nt, one deletion and one substitution using dimethoxytrityl (DMT) nucleoside phosphoramidite chemistry. In detecting single-nucleotide mismatches, fluorescence in situ hybridization of the bead-conjugated probes showed high specificity and signal-to-noise ratios. These preliminary results suggest further possibilities of creating a novel type of versatile, sensitive and multifunctional reconfigurable one-bead one-compound (OBOC) bead array.

We demonstrate the use of holographic optical tweezers for trapping and manipulating silicon nanomembranes. These macroscopic free-standing sheets of single-crystalline silicon are attractive for use in next-generation flexible electronics. We achieve three-dimensional control by attaching a functionalized silica bead to the silicon surface, enabling non-contact trapping and manipulation of planar structures with high aspect ratios (high lateral size to thickness). Using as few as one trap and trapping powers as low as several hundred milliwatts, silicon nanomembranes can be rotated and translated in a solution over large distances.

Single crystal sapphire substrates were lithographically patterned with a system of parallel platinum electrodes, which were used to manipulate 1.58μm silica particles inplane, in the presence of an aqueous solution. Observation of the motion of these particles revealed the adhesion of some of them to the sapphire surface near the platinum working electrode, even in the range of pH where the zeta potentials of silica and sapphire are of the same sign. This phenomenon suggests the existence of localized differences in pH, attributable to the presence of potential determining ions produced in the faradaic processes occurring at the electrodes during the electrophoretic manipulation of silica particles. Atomic force microscopy (AFM) was used to corroborate this hypothesis, measuring the forces between a silica particle and a sapphire substrate in the presence of an applied field. The resultant force-distance curves demonstrate a change in the interaction forces between particle and substrate as a function of distance from the electrode. Variations in this interaction correspond to localized differences in the zeta potential of the substrate, which, in turn, are related to localized differences in pH. Quantification of these spatial variations in pH as a function of time yields further information about the diffusion of these faradaically produced potential determining ions across the substrate.

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is the Director of Wendt Commons, which provides teaching, learning, information and media services in the College of Engineering at the University of Wisconsin-Madison. Prior to assuming responsibility for this new organization, she led the staff of the CoE's Wendt Library in providing engineering library services.