Ultramicroscopic objects, sometimes called sub-microscopic or nanoscopic, are objects too small to be usefully observed with a conventional microscope. This typically refers to objects smaller than about a micron in size, but may refer to bacteria as large as a few microns across. A micron, or micrometer, is a millionth of a meter, followed by the nanometer, which is a billionth of a meter.
The most common means of observing ultramicroscopic objects is the electron microscope, invented in 1931. A couple others include the ultramicroscope, which observes objects smaller than the wavelength of light by observing their diffraction rings against a black body, and the scanning tunneling microscope, which uses quantum effects to image individual atoms.
Some ultramicroscopic lengths and objects include:
- Hydrogen atom - 0.05 nm.
- Sulfur atom - 0.1 nm.
- Diameter of carbon nanotube - 1 nm.
- Diameter of DNA helix - 2 nm.
- 10 base pairs in a typical DNA strand - 3.4 nm.
- Thickness of typical cell membrane - 6-10 nm.
- Smallest viruses - 20 nm.
- Wavelength of extreme ultraviolet light - 40 nm.
- Smallest feature size of present-day microchips - 65 nm.
- Size of typical smoke particles - 100 nm.
- Largest known virus,
- Visible light spectrum (violet) begins - 380 nm.
- Capsid diameter of largest known virus, Mimivirus - 400 nm.
- Diameter of smallest known bacterium, Haemophilus influenzae - 500 nm.
- Informal upper limit of ultramicroscopic regime - 1000 nm.
When the electron microscope first began to be used commercially in the 1940s, one of its first applications was the characterization and description of viruses, which were considered relatively mysterious up until that time. Much of the pioneering research took place in Germany, Canada, and the United States. It was discovered that viruses, along with most other ultramicroscopic objects, do not change in relation to their environments, which is thought to have precluded them from inclusion in the tree of life.
Other uses for ultramicroscopes include the observation of fog particles, and the tracking of ions in cloud chambers, and the study of Brownian motion, which was one of the first topics addressed by Einstein at the start of his physics career.