Just like underground explorers finding their way with head torches, gangs of molecular robots can roam the surfaces of materials, avoiding obstacles and jumping crevices. These roaming nanobots are able to chart surface structure. Researchers at the University of Washington in Seattle have used such nanobots by stacking cylinders of the protein tubulin together to form molecular machines called microtubules. These normally act as scaffolding inside cells, providing a route along which materials are transported by proteins called kinesins.
The Washington team has turned this effect on its head, synthesizing self-propelled nanoscale robots by fixing kinesin molecules all over a surface. The microtubules then propel themselves randomly across the surface. A fluorescent dye added to the microtubules acts as their "head torches", permitting the researchers to track their paths as long as the surface being investigated is transparent to the light emitted.
Microtubule nanobots can probe holes, cavities and pores that cannot be normally seen with a microscope. Their only limitation is steep walls, where they are too rigid for kinesin molecules to guide them. According to the Washington team, custom robots could be designed to study specific aspects of a surface, such as mapping out regions that are hygroscopic. This could help in understanding the structure of porous materials.
The resolution of the Washington nanobots is expected to be around 50 nm. The number and speed (typically 200-250 nm/s) of the robots determines the time taken to explore an accessible surface completely. Superposition of several hundred images enables mapping of the entire surface.
Reference
H Hess, J Clemmens, J Howard and V Vogel 2002 "Surface imaging by self-propelled nanoscale probes" Nano Letters 2 113-116.