Membrane channels as a tool to control nanoreactors.

We present an example of the use of self-assembly of biomolecules to create nanostructured building blocks. The resulting individual compartments can be tailored to fulfil specific functions: catalysis of a chemical reaction in a confined environment, detection on a molecular level and feedback with the outside. For example, such individually designed components can be assembled to build up macroscopic chemically active filters. The main component is membrane channels acting as molecular sieves, able to control the permeation across the capsule wall. We introduce briefly a new microdevice to characterise membrane channels with a future potential for high-throughput screening of channel properties based on automation, parallelisation and the use of microfluidics. Subsequently, we outline a possible application for channel-forming proteins: encapsulation of charged polymers or proteins into liposomes and restriction of diffusion through transmembrane channels to small ions, creating a Donnan potential. This Donnan potential can be used for external manipulation of nanocontainers by coupling of the capsule to an external electric field, or for the selective uptake of small charged molecules into the capsule.