nM
Meaning of nM: A smaller number means a stronger compound, since less of it is needed to produce the same effect.
Definition of nM
nM is the abbreviation for nanomolar, a measure of how concentrated a substance is in a solution. One nanomolar means one billionth of a mole of that substance dissolved in each liter. It is a very dilute concentration, and it is the scale on which laboratories describe how tightly a drug or other molecule binds its target.
How does it fit with the other units?
| Unit | Fraction of one molar | Typical use |
|---|---|---|
| Molar | One | Laboratory stock solutions |
| Millimolar | One thousandth | Blood sugar, sodium, potassium |
| Micromolar | One millionth | Many drug levels in blood |
| Nanomolar | One billionth | Binding strength, several hormones |
| Picomolar | One trillionth | The most potent hormones and binding agents |
Each step down the list divides by a thousand. Molar itself means moles per liter, and a mole is a fixed count of particles, the standard chemists use so that quantities of different substances can be compared on equal footing rather than by weight.
Why is potency reported this way?
Describing a compound by how much of it is present says nothing on its own. What matters is how little is needed. A laboratory measures the concentration at which a substance occupies half its target sites, or halves the activity of an enzyme, and quotes that concentration as the measure of strength. A compound active in the low nanomolar range is far more potent than one needing micromolar concentrations, because a thousandfold less molecule achieves the same result. Reported this way, potency can be compared across compounds that have completely different weights and structures.
How is nanomolar different from nanomole?
They measure different things and are easily confused. A nanomole is an absolute amount of substance, a count of particles, with no reference to volume. Nanomolar is a concentration, an amount within a volume. One nanomole dissolved in one liter gives a one nanomolar solution; the same nanomole in a thousandth of a liter gives a solution a thousand times more concentrated. The abbreviations sit close together as nmol and nM, which is why the distinction is worth holding onto when reading a laboratory report or a research paper.
Also known as
Used in a sentence
The assay reported the compound's activity at a concentration in the low nanomolar range.
Good to know
Nanomolar describes a concentration, an amount within a volume, while a nanomole describes an absolute quantity of substance, a distinction often blurred in casual use even though the two measure different things.
Word origin
Where “nM” comes from
Formed from nano-, from Greek nanos, meaning dwarf, denoting one billionth, combined with molar, referring to a unit of concentration.