One of the problems facing this technology is the confusion about how to define nanotechnology. Most revolve around the study and control of phenomena and materials at length scales below 100 nm and quite often they make a comparison with a human hair, which is about 50 000 to 100 000 nm wide.
For instance, in zero-dimensional (0D) nanomaterials all the dimensions are measured within the nanoscale (no dimensions are larger than 100 nm); in two-dimensional nanomaterials (2D), two dimensions are outside the nanoscale; and in three-dimensional nanomaterials (3D) are materials that are not confined to the nanoscale in any dimension. This class can contain bulk powders, dispersions of nanoparticles, bundles of nanowires, and nanotubes as well as multi-nanolayers. Check our Frequently Asked Questions to get more details.
Some definitions include a reference to molecular nanotechnology and 'purists' argue that any definition needs to include a reference to "functional systems". The inaugural issue of Nature Nanotechnology asked 13 researchers from different areas what nanotechnology means to them and the responses, from enthusiastic to skeptical, reflect a variety of perspectives.
Another important criteria for the definition is the requirement that the nanostructure is manmade, i.e.a synthetically produced nanoparticle or nanomaterial. Otherwise you would have to include every naturally formed biomolecule and material particle, in effect redefining much of chemistry and molecular biology as 'nanotech.