femtomole

A femtomole (fmol) is an SI unit of amount of substance equal to 10^-15 moles. The symbol is fmol. The femto- prefix denotes a factor of 10^-15. One femtomole contains about 6.022×10^8 molecules, using Avogadro's number.

Femtomoles are used to express very small quantities in chemistry, biochemistry, molecular biology, and analytical science. They are common in measurements of tiny amounts of DNA, RNA, peptides, enzymes, or reagents in micro-scale experiments and sensitive detection methods.

Relation to other units: 1 femtomole equals 10^-15 moles. The next larger and smaller common submultiples are 1 picomole (10^-12 moles) and 1 attomole (10^-18 moles).

Mass correspondence: The actual mass corresponding to 1 fmole depends on the substance's molar mass. Mass = molar mass (g/mol) × 1×10^-15. For example, a 50,000 g/mol protein would have a mass of about 5×10^-11 g (0.05 ng) per femtomole, illustrating how femtomoles relate to detectable masses in assay workflows.

In summary, a femtomole is a useful unit for describing extremely small amounts of substance, bridging the scale between nanomoles and even smaller quantities frequently encountered in modern biochemical and analytical techniques.