pikomolar

Pikomolar, abbreviated pM, is a unit of concentration in the metric system equal to one picomole per liter (10^-12 mol/L). The standard term in English is picomolar; pikomolar is a less common variant that may appear in some sources. The prefix pico- denotes 10^-12, and when combined with molarity, it yields picomolar as a measure of solute concentration.

One picomolar corresponds to 1e-12 moles per liter. Equivalently, 1 pM equals 0.001 nanomolar (nM) and 1e-6 micromolar (μM). These relationships reflect the extremely small quantities described by the unit and its use in quantitative chemistry and biochemistry.

In biology and pharmacology, picomolar is commonly used to express very low concentrations of biomolecules, such as ligands, hormones, enzymes, or inhibitors, and to describe high-affinity interactions where dissociation constants (Kd) fall into the picomolar range. Describing biological potency or binding strength at pM levels provides a sense of sensitivity and specificity in experiments.

Measurement at picomolar levels requires sensitive techniques and careful methodology. Methods often employed include fluorescence-based assays, highly sensitive enzyme-linked immunosorbent assays (ELISAs), surface plasmon resonance (SPR), and mass spectrometry, depending on the sample type and required throughput.

See also nanomolar, micromolar, femtomolar, attomolar, molarity, and SI prefixes.

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