Membrane processes for purification are of great industrial interest as they are easy to scale up and may be tailored to individual requirements. Indeed, membranes for highly specific applications are commercial standard, including those with pore sizes in the lower nanometer range. However, to enable filtration with considerable flux, operating nanofiltration membranes usually requires high transmembrane pressures. Current industrial nanofiltration is thus an energy- and cost-intensive process. To overcome this limitation, a new generation of ultrathin, bioinspired nanofiltration membranes is being investigated at Fraunhofer IAP. The new membranes are less than 10 nm thick, which allows for low-pressure nanofiltration and moreover makes our membranes interesting candidates to be applied in biomedical microdevices. The membranes consist of modified variants of the ß‑barrel-shaped channel protein FhuA acting as monodisperse filter pores. FhuA appears in nature as an iron transport protein in bacterial membranes of Escherischia coli (E. coli). In addition to its robust channel structure, the interior of the nanopores may be engineered to fullfil various separation requirements, e.g. size and chirality.

We pursue several approaches for the integration of FhuA into membranes...