  Purple membranes from the archaeon Halobacterium salinarum consist of
two-dimensional crystals of the light-driven proton pump bacteriorhodopsin,
which convert photons into a proton gradient across the cell membrane. This
functional feature and the structural rigidity make them appealing candidates
for integration into biomimetic devices. To this end, and in order to carry out
their function, purple membranes must be positioned in the correct orientation
at the position of interest. Precise placement and control over the orientation
of nanoscale objects still constitutes a formidable challenge. Here we show
that isolated purple membrane patches can be transported and positioned at
predefined locations in nanofluidic confinement, with control over their
orientation at the target sites. The transport is achieved through a rocking
Brownian motor scheme, while the controlled deposition of the membranes is
realized by engineering the surface potential of a fluid-filled nanofluidic
slit. This controlled manipulation of purple membrane patches outlines a new
pathway towards the integration of biological or other delicate supramolecular
structures into top-down-fabricated patterns, for the assembly of nanoscale
hybrid devices that serve as a light-driven source of (chemical) energy.
