Nanopore Filters

The original nanopore (Nuclepore) filters [10,11] are sheets of polycarbonate of 6-11 |im thickness with closely spaced arrays of parallel holes running through the sheet. The filters are available with pore sizes rated from 0.015 Jim - 12.0 |im (15 nm - 12 000nm). The holes are made by exposing the polycarbonate sheets to perpendicular flux of ionizing a particles, which produce linear paths of atomic scale damage in the polycarbonate. Controlled chemical etching is then employed to establish and enlarge the parallel holes to the desired diameter. This scheme is an example of nanotechnology.

The filters are robust and can have a very substantial throughput, with up to 12% of the area being open. The smallest filters will block passage of bacteria and perhaps even some viruses, and are used in many applications including water filters for hikers.

A second class of filters (Anapore) was later established, formed of alumina grown by anodic oxidation of aluminum metal. These filters are more porous, up to 40%, and are stronger and more temperature resistant than the polycarbonate filters. The Anapore filters have been used, for example, to produce dense arrays of nanowires. Nanowires are obtained using a hot press to force a ductile metal into the pores of the nanopore alumina filter.

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