nanometer
Meaning of nanometer: The scale on which molecules, viruses and wavelengths of light are measured, far below anything an ordinary microscope can resolve.
Definition of nanometer
A nanometer is a unit of length equal to one billionth of a meter, written nm. It is the working scale of molecules and viruses: a strand of DNA is about 2 nanometers across, and visible light spans wavelengths of roughly 400 to 700 nanometers. A human hair, by comparison, is tens of thousands of nanometers thick.
How small is it?
A meter divided by a thousand gives a millimeter, the smallest division marked on a ruler. Divide that by a thousand for a micrometer, roughly the width of a bacterium. Divide by a thousand once more and the result is a nanometer. Three steps take the measurement from what the eye can just make out down to the size of individual molecules. The prefix behaves identically wherever it is attached, so a nanogram is a billionth of a gram and a nanosecond a billionth of a second.
What is measured in nanometers?
| Object | Approximate size |
|---|---|
| Water molecule | Under 1 nanometer |
| DNA double helix, across | About 2 nanometers |
| Antibody molecule | About 10 nanometers |
| Virus particle | Tens to hundreds of nanometers |
| Wavelength of visible light | About 400 to 700 nanometers |
| Red blood cell, across | About 7,000 nanometers |
Where does it come up in medicine?
Mostly in imaging and laboratory work. A wavelength stated in nanometers is what a laboratory instrument measures absorbance at, what a laser is selected for, and what a fluorescent stain gives off. Because visible light is itself hundreds of nanometers long, a light microscope cannot separate two objects much closer together than about half a wavelength, so anything smaller has to be viewed with electrons instead. Ultraviolet, visible and infrared light are simply neighboring bands of the same scale, which is why sunscreens and light-based treatments are described by the range of nanometers they cover. Particles built deliberately at this size, called nanoparticles, are used to carry drugs and to change how tissue takes them up.
Also known as
Used in a sentence
The assay measured absorbance at a wavelength of 260 nanometers.
Good to know
The prefix nano always denotes one billionth, so a nanogram and a microgram differ a thousandfold, a distinction that matters wherever laboratory results are reported in either unit.
Word origin
Where “nanometer” comes from
Nano- comes from the Greek nanos, meaning dwarf, and meter from the Greek metron, a measure.