Nanotechnology—inspired by biology—can use catalytic motors to convert chemical to mechanical energy, using fuels that are chemically simpler than ATP—the energy currency of biology—and catalysts that are simpler than enzymes. In a Nanowerk Spotlight, Michael Berger describes nanotech catalytic motors for transporting micron-scale cargo. Excerpts from “Catalytic nanotransporters for nanotechnology applications outside biological systems“:
The catalytic conversion of chemical to mechanical energy is ubiquitous in biology, powering such important and diverse processes as cell division, skeletal muscle movement, protein synthesis, and transport of cargo within cells. Catalytic ‘engines’ will be key components of active micron- and sub-micron scale systems for controlled movement, particle assembly, and separations. …we show an example where catalytic nanomotors can, in principle, be tethered or coupled to other objects to act as the engines of nanoscale assemblies. Additionally, an object that moves by generating a continuous surface force in a fluid can, in principle, be used to pump the fluid by the same catalytic mechanism. Thus, by immobilizing these nanomotors, a group of scientists have developed micro/nanofluidic pumps that transduce energy catalytically.
“Until recently, catalytic micro- and nanomotors have been more or less unknown outside biology” Dr. Ayusman Sen explains to Nanowerk. “For nanotechnology researchers, catalyzed movement on the nanoscale is a fairly new phenomenon and there is much to be learned from nature’s motor systems. There is a good possibility that unexpected applications will arise from exploratory research.”
…”By analogy to biological systems” he says, “we can project some obvious applications of catalytic nanomotors, including: (a) engines for micro/nanoscopic machines, (b) chemotactic roving sensors, (c) delivery vehicles for molecules and nanoparticles, and (d) formation of patterns or arrays by autonomous local deposition of materials.”
Sen’s group has demonstrated that one can build nanomotors ‘from scratch’ that mimic biological motors by using catalytic reactions to create forces based on chemical gradients. These motors are autonomous in that they do not require external electric, magnetic, or optical fields as energy sources. Instead, the input energy is supplied locally and chemically.
…The motor function is not disrupted due to the presence of passive cargo although a decrease in speed was observed. In addition, motors with nickel segments can overcome both Brownian orientational fluctuations and biased rotation of the rod-sphere doublet to enable persistent steerable uniaxial motion in an external magnetic field. The scientists are thus able to control even Brownian motion, at the microscopic level.
…Sen’s work, which is the first examples of nano/microscale objects outside biological systems that move through catalysis, also reveals that chemotaxis (i.e. the movement by a cell or organism in reaction to a chemical stimulus) does not require a sophisticated ‘temporal sensing’ mechanism commonly attributed to bacteria. Rather, the nanoparticles move up a fuel gradient through catalysis; a straightforward extension is movement towards or away from a signaling molecule — a promoter or an inhibitor of the catalytic reaction.
This behavior provides a novel way to direct particle movement towards specific targets, even while allowing them to sample a large region of fluid by apparently diffusive motion. Sen says this discovery is potentially important in the design of ‘smart’ autonomous nano-robots, which could move independently in the direction they are needed, perhaps by harvesting energy from glucose or other abundant fuels in biological or organic systems.
—Jim
