Nanotechnology is a broad range of technologies and products whose characteristic dimensions are less than about 1,000 nanometers. In short, nanotechnology is the engineering of individual molecules and atoms.

How small is nano? A dime is 1,000 microns thick, a human egg cell about 100 microns, a red blood cell about 5 microns, a nerve axon about 1 micron, and a virus about 0.1 micron, or 100 nanometers. DNA molecules are less than 3 nanometers in diameter. Many common proteins are only a few nanometers across. An atom is about 0.1 nanometer.

This is the ultimate version of 3D printing. Atomic force microscopes (AFMs) dip tiny probes with tips a few atoms wide into wells of organic molecules (including carbon and DNA). The probes can 'engrave' or 'write' on a scale of a few nanometers.

Nanofabricators use robot-controlled arrays of thousands or millions of parallel probes to build components for larger microelectromechanical systems, and to create complex nanostructures consisting of a different type of molecules. These include molecular computers, self-assembling 'smart ink' used by 3D printers, and various types of nanomachines.

Molecule-sized assembler robots, made out of diamond, that rearrange atoms to build just about anything are still a holy grail, but smart pseudobiological nanomachines exist. These devices are a fusion of microelectromechanics and biomechanics. For example, light-harvesting mechanisms derived from photosynthesis can create the cellular fuel ATP (adenosine triphosphate), the same molecule that powers our own cells. ATP powers various types of nanomachines optimized for different activities. A simple example is a rotor formed out of proteins and metals nestled in a ring of ATPase proteins (an enzyme used to assemble ATP-based nanomachines). These tiny nanomotors perform various tasks, such as powering tiny pharmaceutical factories that manufacture drugs and pump them to tissues requiring them.

Tiny mobile nanobots perform cellular surgery or protect the body against toxins, disease, and other conditions. They recognize cells via their distinct antigens, much the way the immune system does. Their tasks include cell repair, waste product removal, toxin neutralization, and chemical delivery. A patient is injected with a few cubic centimeters of fluid containing millions of nanobots. Those designed to travel the blood are small (2-3 microns), while those intended to traverse tissue, or intestinal or air passages, are several times larger. A typical device has a protein-based frame and is propelled by bacteria-like cilia or flagella. It possesses tiny rotors for molecular sorting and, in some cases, miniature gas or chemical transport vessels. Depending on its designed function, it will use these nanoscale tools to scrub arteries clear of plaque, eradicate cancers or perform on-site repairs to fix cellular damage, ro deliver chemical signals. Nanobots designed to operate in the body are usually configured to a particular patient to avoid triggering the body's immune system. Other models are either small or fast-acting enough to be ignored, or have 'stealth' coatings that can reconfigure their surface texture to pass as the body's native cells. Nanobots are mostly powered by ATP metabolized from local oxygen and glucose, and do not replicate.