Application of nanopores in polymer foils for gas separation, aerosol collection, and as chemical sensors

Wolfgang Ensinger

Department of Materials Science, Technische Universit?t Darmstadt, Germany

ensinger@ca.tu-darmstadt.de

In order to create nanopores (or nanochannels), foils of polymers such as polyimide or polycarbonate are irradiated with high energy heavy ions such as gold or lead from a linear accelerator. The radiation damage tracks, created by the ions, can preferentially chemically be etched, thus forming nanopores. The areal density of the nanopores can range from one single pore up to 10⁹ pores per cm². The nanopores can be cylindrical or conical, depending on the etching conditions. The length of the nanopores correspond to the thickness of the polymer foil, typically 10 to 40 µm. The cylindrical nanopores have a diameter of typically 20 nm up to several µm. The diameter can freely be chosen and shows a narrow distribution. The conical nanopores have diameters of a few nm of the narrow aperture and open up to several 100 nm at the wide aperture.

Conical nanopores are used as chemical sensors. For this purpose, a biorecognitian element is fixed at the nanopore wall. This is a molecule which reacts with a specific counter molecule. The polymer foil with the modified nanopore is placed inside an electrochemical cell, and the cell current through the nanopore is measured. In the presence of the molecule to be analyzed, the current is changed. Since this happens only with one specific molecule, the nanopore acts as a highly specific and sensitive sensor for it. This concept has been demonstrated with polyallylamine als biorecognitian molecule and streptavidin as analyte molecule. It can be extended to other molecules, which play a role in medicine, such as glucose, thus providing a sensor for biomedical applications.

The cylindrical nanopores can act as nanomembrane filter for various purposes, such as cleaning liquids from bacteria or collecting dust particles from the environment. An example is shown with results from a factory, where it has been evaluated how clean the air is with respect to toxic nanoparticles. Another example is gas separation, where the nanomembrane has been demonstrated to be effective in separating gases from each other, as shown with a model gas mixture system of carbon monoxide and carbon dioxide.

Keywords: Nanopores, nanochannels, aerosol collection, gas separation, chemical sensor

Department of Materials Science, Technische Universit?t Darmstadt, Petersenstr. 23, 64287 Darmstadt, Germany

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