Designing, building, and running molecule-sized nanocars has become an active field of research among nanotechnology scientists. Based on research to reinvent the wheel for nanotechnology, efforts range from the original nano car developed by James Tour at Rice University in 2005 - which had buckyball wheels and flexible axles, and served as a proof-of-concept for the manufacture of machines at the nanoscale - to 'nanodragsters', and a nano car with molecular 4-wheel drive. A new Perspective article in ACS Nano describes how this field began, its growth, and list problems to be solved.
A look at what is happening in the field of artificial nanoscale motors and molecular machinery. These nanomachines could one day perform functions similar to the biological molecular motors found in living cells, things like transporting and assembling molecules, or facilitating chemical reactions by pumping protons through membranes. Researchers have reported a light-powered DNA locomotion device that is capable of autonomous and reversible motion along an oligonucleotide track. The direction of motion can be switched using different wavelengths of light. Compared with other reported DNA walkers, this new strategy not only preserves the autonomous and controllable movement but also provides a reusable track, making it feasible to reset the device after the complete trip, as observed in nature for kinesin and myosin.
Man-made micro- and nanoscale motors have received a tremendous recent interest owing to their great potential for diverse potential applications, ranging from targeted drug delivery, microchip diagnostics or environmental remediation. Particular attention has been given to self-propelled chemically-powered micro/nanoscale motors, such as catalytic nanowires, microtube engines, or spherical Janus microparticles. Although significant progress over the past 10 years has greatly advanced the capabilities of these tiny man-made machines, such catalytic motors have predominantly relied on an external hydrogen peroxide fuel that impedes many practical applications. Researchers have now demonstrated the first example of a water-driven bubble-propelled micromotor that eliminates the requirement for the common hydrogen peroxide fuel.
The catalytic conversion of chemical to mechanical energy, which is ubiquitous in biological systems, also is the basis for many of the engine systems that nanotechnology researchers are developing. Catalytic 'engines' will be key components of active micron- and sub-micron scale systems for controlled movement, particle assembly, and separations. So far, most of these catalytic micro- and nanomotors use hydrogen peroxide as the fuel. The major problem associated with this is that the produced oxygen bubbles make the observation and detailed study of these motors difficult. Researchers at the Pennsylvania State University have now introduced a new bubble-free, high efficient nanomotor system that involves the operation of a miniaturized copper-platinum nanobattery.
Self-propelled motion of engineered nanomaterials can be useful in applications such as bottom-up assembly of structures, pattern formation, microfluidic diagnostic systems, or drug delivery at specific locations. While nature has perfected nano- and microscale motor systems, movement at the nanoscale is still a massively challenging problem for nanotechnology researchers. There are various approaches to creating self-powered micro- and nanosized motors and many researchers have focused on catalytic conversion of chemical to mechanical energy. Whereas the catalytic reactions of small molecules have been the focus of recent nanomotor research efforts, polymerization has not attracted any interest; until now. Researchers describe a new type of micromotor that is powered by a polymerization reaction and deposits tiny threads along its trail like a microspider.
Off-targeting remains a key challenge of researchers working on nanoparticle drug delivery - the majority of intravenously administered therapeutic nanoparticles are also reaching normal tissues, resulting in considerable adverse side effects. Another challenge of nanoparticle drug delivery includes the limited penetration depth of particles into the tumors. While extensive efforts have been devoted for designing therapeutic nanoparticles, a new study - echoing the journey through the human body in Fantastic Voyage - represents the first example of coupling such drug nanocarriers with self-propelled nanoshuttles. The ability of synthetic nanomotors to carry 'cargo' has already been demonstrated; but not in connection to common drug-loaded particles. In a new study, researchers demonstrate that catalytic nanoshuttles can readily pickup common biocompatible and biodegradable drug-loaded particles and liposomes and transport them over predefined routes towards predetermined destination.
For the visionary goals of nanotechnology, functional and perhaps autonomous molecular motors will play an essential part, just like electric motors can be found in many appliances today. These nanomachines could perform functions similar to the biological molecular motors found in living cells, things like transporting and assembling molecules, or facilitating chemical reactions by pumping protons through membranes. Although applications of molecular motors are still in the future, the results of early-day studies are already spectacular: well-designed molecules or supramolecules show different kinds of motion - fueled by different driving forces such as light, heat, or chemical reactions - resulting in molecular shuttles, molecular elevators and rotating motors. A team of researchers is now proposing a conceptually new design of molecular motor based on electric field actuation and electric current detection of the rotational motion of a molecular dipole embedded in a three-terminal single-molecule device.
One of the (many) major challenges in getting closer to realizing visions of skillful nanomachines and ubiquitous nanofactories is the construction of synthetic nanomotors and other nanoscale propulsion systems that power these devices. At issue is not only the small scale of these systems but also the ability to precisely control their motion. Complicating the issue is that navigation principles used in the macroscale world are not applicable for nanoscale propulsion. The precise navigation of nanoscale objects is extremely challenging because of the combination of Brownian motion (random movement of particles) and low Reynolds number (where viscous forces dominate). Researchers in Germany have now demonstrated artificial water-walking devices in the form of self-powered microstriders at the air-liquid interface made of rolled-up catalytic microtubes.