George D. Bachand

Biomolecular motors such as F 1 –adenosine triphosphate synthase (F 1 -ATPase) and myosin are similar in size, and they generate forces compatible with currently producible nanoengineered structures. We have engineered individual biomolecular motors and nanoscale inorganic systems, and we describe their integration in a hybrid nanomechanical device powered by a biomolecular motor. The device consisted of three components: an engineered substrate, an F 1 -ATPase biomolecular motor, and fabricated nanopropellers. Rotation of the nanopropeller was initiated with 2 mM adenosine triphosphate and inhibited by sodium azide.

Biomolecular motors, in particular motor proteins, are ideally suited to introduce chemically powered movement of selected components into devices engineered at the micro- and nanoscale level. The design of such hybrid "bio/nano"-devices requires suitable synthetic environments, and the identification of unique applications. We discuss current approaches to utilize active transport and actuation on a molecular scale, and we give an outlook to the future.

A confluence in scientific advancements associated with molecular biology and nanofabrication technology now offers the potential of engineering functional hybrid organic/inorganic nanomechanical systems. Our objectives were to: (i) establish a system for producing a recombinant biomolecular motor; (ii) precisely position and orient biological molecules on nanofabricated substrates; and (iii) acquire baseline performance data on a biomolecular motor in a hybrid system. A recombinant expression system was established for the large-scale production of a thermostable biomolecular motor, F1-ATPase, modified to contain chemically active `handles.' His tags were used to specifically attach, as well as precisely position and orient, biological molecules on nickel, copper and gold substrates created using electron beam lithography. Further, these substrates were used to attach F1-ATPase and acquire baseline performance data on motor rotation through the attachment of fluorescent microspheres to the tip of the γ subunit. Counterclockwise rotation of the γ subunit was measured at approximately 10 Hz (3-4 rev s-1) using a differential interferometer. These data have established several prerequisite technologies that are essential to the integration of biomolecular motors in nano-electro-mechanical systems. The evolution of these technologies will open the door to the seamless integration of the motive power of life with engineered nanofabricated devices.

Nature has evolved dynamic, non-equilibrium mechanisms for assembling hierarchical complexes of nanomaterials. A critical element to many of these assembly mechanisms involves the active and directed transport of materials by biomolecular motor proteins such as kinesin. In the present work, nanocrystal quantum dots (nQDs) were assembled and organized using microtubule (MT) filaments as nanoscale scaffolds. nQD density and localization were systematically evaluated by varying the concentration and distribution of functional groups within the MT structure. Confining nQD attachment to a central region within the MT enabled unaffected interaction with kinesin necessary to support active transport of nQD−MT composites. This active transport system will be further refined to control the optical properties of a surface by regulating the collective organization of nQD−MT composites.

Nuclear pore complexes (NPCs) regulate all cargo traffic across the nuclear envelope. The transport conduit of NPCs is highly enriched in disordered phenylalanine/glycine-rich nucleoporins (FG-Nups), which form a permeability barrier of still elusive and highly debated molecular structure. Here we present a microfluidic device that triggered liquid-to-liquid phase separation of FG-Nups, which yielded droplets that showed typical properties of a liquid state. On the microfluidic chip, droplets were perfused with different transport-competent or -incompetent cargo complexes, and then the permeability barrier properties of the droplets were optically interrogated. We show that the liquid state mimics permeability barrier properties of the physiological nuclear transport pathway in intact NPCs in cells: that is, inert cargoes ranging from small proteins to large capsids were excluded from liquid FG-Nup droplets, but functional import complexes underwent facilitated import into droplets. Collectively, these data provide an experimental model of how NPCs can facilitate fast passage of cargoes across an order of magnitude in cargo size.