Single stranded DNA (ssDNA) binding protein plays an important role in the DNA replication process in a wide range of organisms. It binds to ssDNA to prevent premature re annealing and to protect it from degradation. Current understanding of SSB/ssDNA interaction points to a complex mechanism, including SSB motion along the DNA strand. We report on the first characterization of this interaction at the single molecule level using solid state nanopore sensors, namely without any labelling or surface immobilisation. Our results show that the presence of SSB on the ssDNA can control the speed of nanopore translocation, presumably due to strong interactions between SSB and the nanopore surface. This enables nanopore based detection of ssDNA fragments as short as 37 nt, which is normally very difficult with solid state nanopore sensors, due to constraints in noise and bandwidth.Notably, this fragment is considerably shorter than the 65 nt binding motif, typically required for SSB binding at high salt concentrations. The non specificity of SSB binding to ssDNA further suggests that this approach could be used for fragment sizing of short ssDNA.
Three dimensional (3D) ion beam lithography (IBL) is used to directly pattern 3D photonic crystal (PhC) structures in crystalline titania. The process is maskless and direct write. The slanted pore 3D structures with pore diameters of 100 nm having aspect ratio of 8 were formed. It is shown that chemical enhancement of titania removal up to 5.2 times is possible in XeF2 gas for the closest nozzle-to-sample distance; the enhancement was ∼ 1.5 times for the actual 3D patterning due to a sample tilt. Tolerances of structural parameters and optimization of IBL processing required for the fabrication of PhCs with full photonic bandgap in visible spectral range in rutile are outlined. Application potential of 3D-IBL is discussed.
Fresnel Zone Plates (FZP) are to date very successful focusing optics for X-rays. Established methods of fabrication are rather complex and based on electron beam lithography (EBL). Here, we show that ion beam lithography (IBL) may advantageously simplify their preparation. A FZP operable from the extreme UV to the limit of the hard X-ray was prepared and tested from 450 eV to 1500 eV. The trapezoidal profile of the FZP favorably activates its 2 nd order focus. The FZP with an outermost zone width of 100 nm allows the visualization of features down to 61, 31 and 21 nm in the 1 st , 2 nd and 3 rd order focus respectively. Measured efficiencies in the 1 st and 2 nd order of diffraction reach the theoretical predictions.
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A method for practical area upscaling of nanopatterning for light-harvesting and photocatalytic applications is presented. Large area electron beam lithography is used to design patterns of simple-shape nanoparticles. After evaporation of gold, ion beam lithography is used to slice nanoparticles with grooves as narrow as 17 +/- 3 nm in width for the required spectral performance and light field enhancement. It is demonstrated by systematic numerical simulations that cutting grooves into the Si and SiO(2) substrates up to a similar to 10 nm depth augments the volume where the light-field enhancement occurs. The dominant component of the field enhancement in the groove is vertical bar E(z)vertical bar(2), perpendicular to the substrate's surface. The application potential of 3D-tailored nanoparticles in light harvesting applications is discussed
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