A confluence in the advancement of the science associated with molecular biology and nanofabrication technology now offer for the first time the potential of engineering functional hybrid organic/inorganic nanomechanical systems. Scientists have been studying a wide range of organic molecular motors for some time. Also during recent years inorganic, largely silicon based, micromechanical devices have been pursued as useful devices. Only very recently has the size scale of nanofabricated inorganic mechanical devices approached a size scale that could conceivably be compatible with the forces and dimensions of molecular motors. We will present the results of our efforts to take advantage of the best attributes associated with both the inorganic and organic worlds to create and study new types of functional mechanical nanostructures powered by molecular motors and chemical energy sources.
In March, 1997 Noji et al. demonstrated conclusively that the subunit of the membrane protein F1-ATPase rotated in response to the synthesis/hydrolysis of ATP. Not only was this the first rotary motor enzyme ever found, the force generated by this motor protein (>100 pN) is among the greatest of any known molecular motor. With a calculated no-load rotational velocity of 17 r.p.s. and a diameter of less than 12 nm, the F1-ATPase protein is a tailor made nano-motor. These properties coupled with the fact that F1-ATPase is automatically synthesized using the machinery of life, opens the door to the potential of creating chemically powered nanomechanical devices.Integration of the nanoscale bio-compatible lithographic processes pioneered within our group with biological molecular motors may provide the means for creating a transparent interface between the organic/inorganic world. Because both the F1-ATPase biomolecular motor is produced by cellular physiology and the scale of Nano-Electro-Mechanical (NEMS) is considerably smaller than that of a single cell, it may be possible to insert the NEMS into a cell where the motor and NEMS could be self-assembled by the host cell's physiology. The host cell's physiology could also provide power for the device in the form of ATP and maintain the system by replacing the molecular motors when they cease to function. Our goal is to design, build and demonstrate nanoscale engineered systems that harness the mechanical motion of the biological motor protein F1-ATPase. We envision that F1-ATPase motors will be used to pump fluids and open and close valves in microfluidic devices and, provide mechanical drives for a new class of nanomechanical devices
Two scientific obstacles had to be overcome before it was possible to consider powering engineered silicon devices with motor proteins. First a system for modifying and producing F1-ATPase motor protein in a stable form suitable for harnessing the power generated by this enzyme had to be developed. We have successfully developed a system to express an engineered form of the thermophilic Bacilus PS3 F1-ATPase protein in E. coli. This protein expression system provides a flexible platform from which we can engineer different "chemical" handles on the protein, thus establishing a means to integrate the molecular motor with NEMS.. The second challenge was the development of a methodology to precisely attach proteins to NEMS. Our group has pioneered the development of electron beam lithography with organic monolayers. This surface chemistry modification process is compatible with both biological molecules and semiconductor manufacturing processes. It facilitates the placement of either single groups or designed patterns of molecules with a precision approaching 15 nm. This technology has been used to place "hands" on the NEMS that are used to grab the "handles" engineered into the F1-ATPase motor protein thus providing a mechanism for appropriately uniting the organic and inorganic components of the hybrid systems. Optical instruments have also been developed in our laboratory to both manipulate nanometer scale objects and observe nanometer scale motion. We thus now have the capability to create and observe the motion of inorganic-organic mechanical devices with nanometer resolution.
Despite the superb performance of the F1-ATPase motor protein, little is truly known about how this enzyme generates rotary motion. Neither the useful life of the motor nor the impact of local environmental variables on the protein has been explored. The impact of motor generated waste products (i.e. protons and heat) and the effects of load on the performance and life of the motor need to be identified. A rigorous evaluation of the engineering properties of the F1-ATPase motor protein necessitates the development of assays that provide consistent measurements of the performance of the F1-ATPase motor protein under different operating conditions. Our energies are now focused on integrating the F1-ATPase motor protein with NEMS specifically designed to evaluate motor performance. We will present the results of this effort to construct a hybrid organic/inorganic nanoscale system that both provides insight into the basic mechanics of motor protein motion and establishes a technological foundation for functionally integrating these molecules with manufactured devices.
Noji, H., Yasuda, R., Yoshida, M., and Kinosita, K., Jr. (1997). Nature386, 299-302.
This work was performed in part at the Cornell Nanofabrication Facility (a member of the National Nanofabrication Users Network) which is supported by the National Science Foundation under Grant ECS-9319005, Cornell University and industrial affiliates.
Carlo D. Montemagno
304 Riley-Robb Hall, Dept. of Agricultural and Biological Engineering
Cornell University, Ithaca, NY 14853