Selective transport of molecules through membrane is a prerogative of biological systems that is still far from being matched by nanoscale human manufacturing. Here we report our attempt to define a system based on pored silicon nitride membranes and mobile transporters for the selective recognition and import of nanosized objects (proteins, quantum dots, latex particles) from an external compartment. The system uses paramagnetic beads, modified to recognize specific target molecules, which are delivered to arrays of precisely milled pores. After capture of their target, the loaded transporters are removed from the pore and replaced. Prototypes that make use of electrophoretic or electromagnetic forces to mobilize the beads have been constructed and evaluated.