Ultramicroscopic objects are too small to be seen with a conventional microscope and can be observed with an electron microscope, ultramicroscope, or tunneling microscope. Examples include atoms, viruses, and smoke particles. The electron microscope was first used to study viruses in the 1940s. Ultramicroscopes are also used to study fog particles and Brownian motion.
Ultramicroscopic objects, sometimes called submicroscopic or nanoscopic, are objects that are too small to be usefully observed with a conventional microscope. This typically refers to objects smaller than about a micron in size, but can refer to bacteria as large as a few microns in diameter. A micron, or micrometre, is one-millionth of a metre, followed by the nanometer, which is one-billionth of a metre.
The most common means of observing ultramicroscopic objects is the electron microscope, invented in 1931. A couple of others include the ultramicroscope, which looks at objects smaller than the wavelength of light by looking at their diffraction rings against a blackbody, and the tunneling microscope, which uses quantum effects to represent individual atoms.
Some ultramicroscopic lengths and objects include:
Hydrogen atom – 0.05 nm.
Sulfur atom – 0.1 nm.
Carbon nanotube diameter – 1 nm.
DNA helix diameter – 2 nm.
10 base pairs in a typical DNA strand – 3.4 nm.
Typical cell membrane thickness – 6-10 nm.
Smallest viruses – 20 nm.
Wavelength of extreme ultraviolet light – 40 nm.
The minimum feature size of current microchips: 65 nm.
Typical smoke particle size – 100 nm.
The largest known virus,
Visible (violet) light spectrum begins – 380 nm.
Capsid diameter of the largest known virus, Mimivirus – 400 nm.
Diameter of the smallest known bacterium, Haemophilus influenzae – 500 nm.
Informal upper limit of the ultramicroscopic regime – 1000 nm.
When the electron microscope began to be used commercially in the 1940s, one of its first applications was the characterization and description of viruses, which had hitherto been considered relatively mysterious. Much of the pioneering research took place in Germany, Canada and the United States. Viruses, along with most other ultramicroscopic objects, have been found to not change in relation to their environments, which is thought to have precluded their inclusion in the tree of life.
Other uses for ultramicroscopes include observing fog particles and tracking ions in cloud chambers and studying Brownian motion, which was one of the first topics Einstein addressed early in his career as a physicist.
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