Advances in micro- and nanoscale engineering have led to various mobile devices that either can move on solids or swim in fluids. Researchers are applying various strategies to designing nanoscale propulsion systems by either using or copying biological systems such as the flagellar motors of bacteria or by employing various chemical reactions. Many of these approaches are fairly complex and not necessarily suited for large-scale deployment in practical applications. Scientists have theorized about simpler designs for mechanical swimmers that avoid the complexities of biological mechanisms and use very few degrees of freedom.
Researchers in Spain have now demonstrated the experimental realization of a simple device made by microscopic colloidal particles which can be externally controlled and propelled at low Reynolds number condition, i.e. when the viscosity of the fluid dominates over the inertia of the object. This is the same condition that governs the motion of bacteria such as E. Coli or other micro- or nanoscale objects that move in a fluid.
Nanotechnology researchers are actively working on the beginnings of various nanorobotic systems that one day could lead to automated, assembly-line type nanofabrication processes. Last year we reported on a nanogripper, a kind of a robotic 'hand' some ten thousand times smaller than a human hand. This 'pick-and-place' device used a silicon gripper which was controlled by a nanorobotic arm and was capable of picking up a carbon nanofiber and fix it onto the tip of an atomic force microscope cantilever. One of the problems that is vexing researchers is that the nanoscale miniaturization of these grippers comes at the cost of reduced strength - the smaller the gripper, the weaker it becomes. Therefore what is needed is a gripper design that is strong enough yet sufficient flexible and small to handle tough materials like carbon nanotubes.
A major issue for using self-contained nanodevices, for instance as implantable nanosensors or environmental monitoring devices, is the question of how to power these tiny machines with an independent power source. Options include nanobatteries and nanogenerators that harvest energy from their environment. By converting mechanical energy from body movement, engine vibrations, or water or air flow into electricity, these nanoscale power plants could make possible a new class of self-powered medical devices, sensors and portable electronics. Probably the leading team that is driving forward the work on nanogenerators for converting mechanical energy into electricity is Zhong Lin Wang's group at Georgia Tech. Wang's team has now designed and demonstrated an innovative approach to fabricating a nanogenerator by integrating nanowires and pyramid-shaped nanobrushes into a multilayer power generator. By demonstrating an effective way for raising the output current, voltage and power, this work provides the technological platform for scaling up the performance of nanogenerators to a level that some day might be able to independently power devices like pacemakers or iPods.
The concept of a 'machine' - a mechanical or electrical device that transmits or modifies energy to perform a certain task - can be extended to the nano-world. On the nanoscale, the nanomachine components would be atomic or molecular structures each designed to perform a specific task which, all taken together, would result in a complex function. However, these nanomachines can not be built by just further miniaturizing machine blueprints from the macro-world. Functional nanomachinery will need to take into account the quantum effects that dominate the behavior of matter at the nanoscale, affecting the optical, electrical and magnetic behavior of materials. Scientists in The Netherlands are now reporting how an atomic scale mechanical device consisting of two moving parts, each composed of only two atoms can be controlled by an external electrical signal, while being stable and providing a variety of functional modes. They jokingly refer to it as playing atomic pinball, since the two moving parts resemble the flippers in a pinball machine - unfortunately they haven't got a ball yet to play with.
For nanoelectronics applications like single-electron devices to become practical, everyday items, they need to move from the highly individual and customized fabrication process typically found in laboratories to an automated, high-throughput and industrial-scale production environment. The reason this hasn't happened yet is that the various nanoscale pattern definition techniques used today - such as e-beam lithography, mechanically controllable break junctions, electromigration, electrodeposition, nanoscale oxidation, and scanning tunneling microscopy - generally are not suitable for large-scale parallel processing. The fabrication of single-electron devices requires nanoscale geometrical arrangement of device components, that is, source and drain electrodes and Coulomb islands. Developing methods to fabricate nanoscale devices in large numbers at a time has been one of the major efforts of the nanotechnology community. A new study now demonstrates that this can be done with complete parallel processing using CMOS-compatible processes and materials. Furthermore, these single-electron devices can operate at room temperature, an essential requirement for practical implementations.
Borrowing from nature's micro- and nanoscale propulsion systems, nanotechnology researchers have successfully used motor proteins to transport nanosized cargo in molecular sorting and nano-assembly devices. In so-called gliding assays, surface-attached motors propel cytoskeletal filaments, which in turn transport a cargo. However, cargo and motors both attach to the filament lattice and will affect each other. While an effect of cargo loading on transport speed has been described before, it has never been explained very well. To study this effect, scientists in Germany have observed single kinesin-1 molecules on streptavidin coated microtubules. They found that individual kinesin-1 motors frequently stopped upon encounters with attached streptavidin molecules. This work helps to understand the interactions of kinesin-1 and obstacles on the microtubule surface. An interesting, possibly even more important side result is that this understanding will not only help to optimize transport assays, balancing speed and cargo-loading, but can be used as a novel method for the detection of proteins as well.
The motor proteins of the cytoskeleton accomplish nanotransport tasks by moving 'cargo' along microtubules that are about 25 nm wide but can grow up to 1,000 times as long. Nanotechnology engineers are fascinated by this transport mechanism and several efforts are underway in various labs to unravel and, researchers hope, eventually copy nature's engineering feat. A particularly promising setup consists of surface-attached linear motor proteins that drive the motion of cytoskeletal filaments. Some researchers expect that artificial molecular transport systems which utilize microtubules motility will be an alternative to pressure-driven or electrokinetic flow-based microfluidic devices. Researchers in Germany describe a novel method to characterize the rotational movement of cytoskeletal filaments gliding over motor-coated substrate surfaces. This technique allows exploring the detailed paths that motors take on cytoskeletal filaments. This is also important in understanding situations of heavy intracellular traffic, where motors might have to switch lanes.
A fast-growing body of nanotechnology research is dedicated to nanoscale motors and molecular machinery. The results of these studies are spectacular: well-designed molecules or supramolecules show various movements upon exposure to various stimuli, such as molecular shuttles, molecular elevators and molecular motors. So far, however, nobody has been able to directly observe the movements of these molecular machines and utilize the mechanical work done by them. Now, an international group of researchers have succeeded in amplifying the minuscule change in structures at a molecular level caused by an external stimulus (light) to a macroscopic change through a cooperative effect of liquid crystals. Using liquid-crystalline elastomers (LCEs) ? unique materials having both properties of liquid crystals (LCs) and elastomers ? the scientists have successfully developed new photomechanical devices, including the first light-driven plastic motor. In other words, with this novel material the energy from light can be directly converted into mechanical work without the aid of batteries, electric wires, or gears.