Nanopore integrated nanogaps for DNA detection.

A high-throughput fabrication of sub-10 nm nanogap electrodes combined with solid-state nanopores is described. These devices should allow concomitant tunneling and ionic current detection of translocating DNA molecules. We report the optimal fabrication parameters in terms of dose, resist thickness, and gap shape that allow easy reproduction of the fabrication process at wafer scale. The device noise and current voltage characterizations performed and the influence of the nanoelectrodes on the ionic current noise is identified. In some cases, ionic current rectification for connected or biased nanogap electrodes is also observed. In order to increase the extremely low translocation rates, several experimental strategies were tested and modeled using finite element analysis. Our findings are useful for future device designs of nanopore integrated electrodes for DNA sequencing.

Nanolithographic templates using diblock copolymer films on chemically heterogeneous substrates.

The orientation of the lamellae formed by the phase separation of symmetric diblock copolymer thin films is strongly affected by the wetting properties of the polymer blocks with respect to the substrate. On bare silicon wafers the lamellae of polystyrene-b-polymethylmethacrylate thin films tend to order parallel to the wafer surface, with the polymethylmethacrylate block preferentially wetting silicon. We have developed a methodology for inducing the arrangement of lamellae perpendicular to the substrate by using chemically modified substrates. This is done by chemisorbing a self-assembled monolayer of thiol-terminated alkane chains on thin gold films deposited on silicon wafers. We also show that it is possible to spatially control the perpendicular orientation of the lamellae at sub-micron length scales by using simple chemical patterns and etch them, in order to produce nanolithographic templates. This method may be of great technological interest for the preparation of well-defined templates using block copolymer thin films.

ssDNA binding reveals the atomic structure of graphene.

We used AFM to investigate the interaction of polyelectrolytes such as ssDNA and dsDNA molecules with graphene as a substrate. Graphene is an appropriate substrate due to its planarity, relatively large surfaces that are detectable via an optical microscope, and straightforward identification of the number of layers. We observe that in the absence of the screening ions deposited ssDNA will bind only to the graphene and not to the SiO(2) substrate, confirming that the binding energy is mainly due to the π-π stacking interaction. Furthermore, deposited ssDNA will map the graphene underlying structure. We also quantify the π-π stacking interaction by correlating the amount of deposited DNA with the graphene layer thickness. Our findings agree with reported electrostatic force microscopy (EFM) measurements. Finally, we inspected the suitability of using a graphene as a substrate for DNA origami-based nanostructures.

Vertical arrays of nanofluidic channels fabricated without nanolithography.

Vertical arrays of sealed nanofluidic channels, in which both cross-sectional dimensions are controllable down to 10 nm, were fabricated by selective side etching of a SiGe heterostructure comprised of layers of alternating Ge fractions. Capillary filling of these nanochannel arrays with fluorescent dye solutions was investigated using a confocal microscope. The feasibility of using nanochannels for size-based separation of biomolecules was demonstrated by imaging aggregates of tagged amyloid-beta peptide. The ability to integrate a large number of nanochannels shows promise for high throughput applications involving lab-on-a-chip systems.