Placement and orientation of individual DNA shapes on lithographically patterned surfaces

Artificial DNA nanostructures show promise for the organization of functional materials to create nanoelectronic or nano-optical devices. DNA origami, in which a long single strand of DNA is folded into a shape using shorter 'staple strands', 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 ±10° (on diamond-like carbon) or ±20° (on SiO_2)

Biomechanical analysis of the cephalomedullary nail versus the trochanteric stabilizing plate for unstable intertrochanteric femur fractures

© IMechE 2016. Unstable intertrochanteric fractures are commonly treated with a cephalomedullary nail due to high failure rates with a sliding hip screw. The Omega3 Trochanteric Stabilizing Plate is a relatively new device that functions like a modified sliding hip screw with a proximal extension; however, its mechanical properties have not been evaluated. This study biomechanically compared a cephalomedullary nail, that is, Gamma3 Nail against the Omega3 plate. Unstable intertrochanteric fractures were created in 24 artificial femurs. Experimental groups were as follows: Nail (i.e. Gamma3 Nail) (n = 8), Plate A (i.e. Omega3 plate with four distal non-locking screws and no proximal locking screws) (n = 8), Plate B (i.e. Plate A plus five proximal locking screws) (n = 8), Plate C (i.e. Omega3 plate with three distal locking screws and no proximal locking screws) (n = 8), and Plate D (i.e. Plate C plus five proximal locking screws) (n = 8). All specimens were stiffness tested, while the Nail and Plate D groups were also strength tested. For lateral bending, Plate B was less stiff than the Nail (p = 0.001) and Plate A (p = 0.009). For torsion, Plate A was less stiff than Plate D (p = 0.020). For axial compression, the Nail was less stiff than Plate A (p = 0.036) and Plate B (p = 0.008). Axial strength for the Nail (5014 ± 308 N) was 66% higher than the Plate D construct (2940 ± 411 N) (p \u3c 0.001). All Nails failed by partial or complete cutout through the femoral head and neck, but Plate D failed by varus collapse and deformation of the lag screw. When the cephalomedullary nail is clinically contra-indicated, this study supports the use of the Omega3 plate, since it had similar stiffness in three test modes to the Gamma3 Nail, but had lower strength. Stability of Omega3 plate constructs was not improved with locked fixation proximally or distally

Combining Very Large Quadratic and Cubic Nonlinear Optical Responses in Extended, Tris-Chelate Metallochromophores with Six π-Conjugated Pyridinium Substituents

We describe a series of nine new complex salts in which electron-rich Ru" or Fe" centers are connected via jr-conjugated bridges to six electron-accepting N-methyl-/N-arylpyridinium groups. This work builds upon our previous preliminary studies (Coe, B. J. J. Am. Chem. Soc. 2005, 127, 13399-13410; J. Phys. Chem. A 2007, 111, 472-478), with the aims of achieving greatly enhanced NLO properties and also combining large quadratic and cubic effects in potentially redox-switchable molecules. Characterization has involved various techniques, including electronic absorption spectroscopy and cyclic voltammetry. The complexes display intense, visible d -→.π * metal-to-ligand charge-transfer (MLCT) bands, and their π →.π* intraligand charge-transfer (ILCT) absorptions in the near-UV region show molar extinction coefficients as high as ca. 3.5 × 103M-1 cm1. Molecular quadratic nonlinear optical (NLO) responses ß have been determined by using hyper-Rayleigh scattering at 800 and 1064 nm and also via Stark (electroabsorption) spectroscopic studies. The directly and indirectly derived ß values are very large, with the Stark-based static first hyperpolarizabilities ß0 reaching as high as ca. 10 -27 esu, and generally increase on extending the π-conjugation and enhancing the electron-accepting strength of the ligands. Cubic NLO properties have also been measured by using the Z-scan technique, revealing relatively high two-photon absorption cross sections of up to 2500 GM at 750 nm