Nanotechnology, nanotech for short, is the field of microscale engineering that deals with dimensions and tolerances of less than 100 nanometres, especially the manipulation of individual atoms and molecules.
Devices called Nanites were originally conceived of as microscopic machines that could assemble anything with atomic precision, first proposed by Eric Drexler in his 1986 popular book Engines of Creation, followed in 1992 by the more technical Nanosystems and by books by others. Drexler and co-worker’s ideas and writings became an incredibly influential trope in Hard SF in the 90s, replacing the cyberpunk craze of the 80s and early 90s with a new Transhumanist science fiction.
There have been practical suggestions, for example microscopic machines travelling through the bloodstream, curing illness and targetting cancer cells.
But in the end, especially in science fiction, it became equivalent to handwavium and Clarke’s Third Law (any sufficiently advanced technology is indistinguishable from magic; magic here meaning “wave a magic wand”, not actual applied occultism and hermeticism), which created a reaction against excessively nano-heavy SF.
More than 30 years on, no progress has been made with Drexler’s molecular assemblers. Certainly it is possible to move individual atoms, that’s what an atomic force microscope (itself a scifi-like gizmo!) does. But instead nanotech has become commercialised in the form of fancy new materials and enhancements to toothpaste, sunblock and non-stain paint.
And whereas “wet” or enzyme- and solvent-based nano is obviously technologically viable (after all, life is a form of wet nano – consider the astonishing machinery within a single cell!), there is some debate over whether a mechanistic and industrial “dry” nanotech (inanimate machines built from individual atoms on a sub-microscopic level) is possible. Richard Smaley, the Nobel-prize winning chemist who discovered Carbon 60, the third state of carbon and ironically therefore a foundation-stone of nanotech, argues that real world chemistry simply doesn’t conform to Drexler’s drytech engineering and computer design premises. Drexler argues that using ultra-rigid materials it is possible to engineer around this problem. The whole thing apparently degenerated into a slanging match with each shouting over the other. If you like dry nano and idea of self-replicating assemblers (this is the premise for example in the Orion’s Arm universe, at the time I was very pro-Drexler), you’ll totally accept Drexler and co-worker’s rebuttals of Smaley and traditional Transhumanist memes. If you feel that chemistry trumps macro-scale industrialisation on the atomic scale, you’ll go for Smaley and a bionano-based technology (at present I am tend to this position).
It is perhaps likely that both arguments have some viability, but that dry nano will never be a Clarke’s 3rd Law magic wand, wet nano will evolve to have dry aspects, and the two will meet at some point.