Nanopore Fabrication

A new nanopore sequencing approach is currently under development by IBM based on nanometer artificial nanopores fabricated by e-beam drilling in 10-nm-thick membranes made of titanium nitride, separated by insulating layers of silica (3). As the DNA strand is driven through the nanopore, the... 

Hozumi A., Sugimura H., Hiraku K., Kameyama T., Takai O. Micropatterned silica films with ordered nanopores fabricated through photocalcination. Nano Lett. 2001 1 395-399 Hozumi A., Yokogawa Y., Kameyama T., Hiraku K., Sugimura H., Takai O., Okido M. Photocalcination of mesoporous silica films using vacuum ultraviolet light. Adv. Mater. 2000 12 985-987... 

This is an order of magnitude less than the limit set by the noise of the nanopore, showing the key role of the electronic instrumentation. Careful design of the nanopore device is therefore required to avoid a dramatic reduction of the useful bandwidth due to a large pore capacitance. In particular, in the case of a solid-state nanopore fabricated on a silicon substrate it is necessary to take into account the stray capacitance added by the conductive substrate. To clarify this aspect, let us consider the simplified device sketched in Fig. 11a based on a free-standing 50 pm x 50 pm membrane in silicon nitride (thickness t = 20 nm) grown on a silicon substrate. 

Fig. 11 (a) Simplified scheme of a solid-state nanopore fabricated onto a silicon substrate. The top electrolyte reservoir is defined using a gasket, the bottom electrolyte reservoir is assumed in contact with the full silicon chip. The main parasitic capacitances are sketched in part (b) of the figure. 

The authors thank Kevin Ewsuk, Chris DiAntonio, Terry Garino, Dale Zschiesche and Denise Bencoe of Sandia National Laboratories for fabricating the ceramics and performing the N2 adsorption measurements.a. F.M. and D. O. K. thank Dr. Doug Smith of Nanopore Inc. for fabrication of the fumed silica samples, and S. D. B. thanks Dr. Eiichi Fukushima of New Mexico Resonance and Dr. Mark... 

Horvath, R. Pedersen, H. C. Skivesen, N. Svanberg, C. Larsen, N. B., Fabrication of reverse symmetry polymer waveguide sensor chips on nanoporous substrates using dip floating,... 

The Russell group has applied the template synthesis approach to nanoporous films generated from UV-treated PS-fo-PMMA copolymers [43, 147,233,235,241], which were pre-aligned perpendicular to the substrate by an electric field. Through direct current electrodeposition, they fabricated high-density vertical arrays of ferromagnetic cobalt nanowires (Fig. 10a) [43]. Through subsequent work, they also demonstrated the successful replication... 

Metal oxide nanotubes have been synthesized by a diverse variety of fabrication routes. For example titania nanotubes, and nanotube arrays, have been produced by deposition into a nanoporous alumina template [48-51], sol-gel transcription using organo-gelators as templates [52,53], seeded growth [54], hydrothermal processes [55-57] and anodic oxidation [58-65]. 

It should be mentioned that alternative possibilities to prepare similar membranes include the use of a porous alumina membrane as matrix, with the titania nanotubes grown in the channels. Nanoporous alumina membranes are commercial products, also synthesized by anodic oxidation. The commercial Whatman Corporation anodic membrane has holes of about 20-nm diameter at the top of the membrane and about 200-nm diameter at the bottom of membrane. Within these pores Ti02 nanotubes fabricated by template synthesis and water vapour hydrolysis could be grown, but non-uniform membrane characteristics are obtained due to the non-uniform pores of the commercial alumina... 

To avoid penetration and filament formation via static and randomly scattered pinholes, one approach is to diminish the area of the junction until statistically the presence of a pinhole defect is near vanishing, as might be calculated by a Poisson distribution. An example of this strategy is the use of a nanopore junction of 50 nm diameter, though in this case the device fabrication yields were still reported to be quite low, down to a few percent [16]. 

The beauty of organic chemistry is that practitioners can easily make hundreds of different molecules by changing the structure of one partner in a multi-step synthesis. The problem is that the pace of synthesis can easily overrun the ability of the device engineers to test the molecules in the appropriate testbeds. Nanopores are not easy to fabricate and the yield of working devices is not very high. The development of testbeds that can be fabricated reproducibly in high yields is work that in ongoing in many labs. 

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