fM
femtomole per liter
Molar concentrationexact by definition
The femtomolar is 10⁻¹⁵ mol/L, the detection floor of the most sensitive immunoassays and of single-molecule counting techniques. At 1 fM a microlitre contains fewer than a thousand molecules, which is where concentration starts to be a statistical rather than a bulk statement.
Watch out: Below about a picomolar, adsorption onto the walls of the tube removes a meaningful fraction of the analyte. A femtomolar standard is only femtomolar if the vessel has been passivated.
| 1 fM | 1.0000000e-15 M |
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