'Viropore-Membranes' - Talk I: Solid state membrane pores as base for electrochemically driven insertion of bio-nanorings – a “pore-in-pore” membrane preparation approach

Nanoporous membranes are of increasing interest for many applications such as molecular filters, biosensors, nanofluidic logic, and energy conversion devices. To meet highest standards e.g. in molecular separation processes, membranes with pores well defined in terms of pore diameter and chemical properties are coercively required. However, the preparation of membranes with narrow pore diameter distributions is still challenging. In the work presented here, we demonstrate a novel “pore-in-pore” approach. The conical pores of a solid state membrane (SSM) template, produced by a multi-step top-down lithography procedure, are used to insert precisely formed bionanorings with exactly defined inner and outer diameters and protein surfaces. The RNA-stabilized porous 'disks' are prepared from natural building blocks of tobacco mosaic virus (TMV) particles and are tailored for the intended insertion and immobilization in the solid pores, to be achieved by means of silica serving as 'bionic glue' (see 'Viropore-Membranes' project talk II, Wege et al. ). The disks consist of a defined number of TMV coat proteins (CPs), have an outer diameter of 18 nm and a central pore with a diameter of 4 nm in the case of natural wild type CPs. ... mehrWe demonstrate that the insertion of the disks into the pores can be driven either by diffusion due to a concentration gradient, or by applying an electric field along the cross section of the solid state membrane. During the insertion process, the disks diffuse through the bigger apertures of the funnel-like pores until they are trapped inside the “bottle neck”. It is shown that electrophoresis-driven insertion is significantly more effective than insertion via a concentration gradient only. The insertion of the nanodisks into the SSM during the electrophoresis is followed online by recording the current flow across the membrane cross section over time, which is decreasing with an increasing number of disks occupying the membrane pores.