Nanomachines are machines of dimensions in the range of nanometers. They include micro scale replicas of present day machines like the nanogears,nanoarms or the nanorobots as well as futuristic machines which have no present day analogs, like the assembler which can assemble atoms to produce further machines or assembler themselves.

Though there can be analogous of today's mechanical components, the way in which both these categories are manufactured will be entirely in contrast to each other with regard to what we an call as the direction of manufacturing While today's machines are manufactured by the top-bottom approach in which they are machined down from larger components or bulk of the component materials , nanomachines will be manufactured by the bottom-top approach where they are built atom by atom, placing the individual atoms precisely at the required positions.

No nanomachines in the true sense have yet been manufactured, although feasibility of producing several of them is confirmed by various means. The main difficulty lies in the inability of today's handling facilities to account for manipulating such sub atomic particles. Producing them by means of chemical reactions is the most apt one for controlling atomic positions. Scientists have been able to obtain virtual machines by means of computer simulated chemical reactions and this proves their feasibility. The distance from actually making them will be bridged by finding way to control and predict the outcome of chemical reactions more quickly and precisely.

Synthesis Of Nanomachines

The present generation micromachines which fall in the category of nanomachnes in the sense that they are made by molecular technology are currently synthesized by means of chemical reactions. As of now, chemical synthesis is conducted almost exclusively in solution, where reagent molecules move by diffusion and encounter one another in random positions and orientations.

The prominent synthesizing techniques can be classified as follows-

•  Solution-phase synthesis

•  Enzymatic synthesis

•  Mechanosynthesis

•  Biosynthesis

Solution-phase synthesis poses familiar problems of reaction specificity. Although many small-molecule reactions proceed cleanly and have high yields, large molecules with many functional groups present multiple potential reaction sites and hence, can be converted into multiple products.

Although a spectrum of intermediate cases can be identified, enzymatic synthesis differs significantly from the standard solution-phase model. Enzymatic reactions begin with reagent binding, which places molecules in well-controlled positions and orientations. The resulting high effective concentrations resulting high reaction rates.

Mechanosynthesis differs from enzymatic catalysis, yet many of the same principles apply. One can perform mechanosynthesis by using macroscopic devices, such as scanning tunneling and atomic force microscope (STM and AFM) mechanisms. The first clear example of a mechanically controlled synthesis was the arrangement of 35 Xenon atoms on a nickel crystal to spell ‘IBM'.

Biosynthesis involves synthesize of biological materials.