Microion

Microion is a term used in some scientific contexts to refer to a small ion or to ions within a micro-scale ionic environment. It is not a standard, universally defined term with a single fixed meaning, and its precise interpretation varies by discipline and source. In general, microions are the ions involved in processes or devices that operate at microscopic scales, such as microfabricated systems, microfluidic channels, or microelectrode applications.

In neuroscience and pharmacology, the related technique of microiontophoresis employs tiny currents to eject charged molecules from a glass or micropipette. In discussions of this method, the ions delivered from the pipette—often including neurotransmitters or drug ions—are sometimes referred to as microions. The amount delivered is controlled by the applied current and duration of application.

In electrochemistry and colloidal science, microions can denote the small counterions and co-ions that populate electrolyte solutions within confined or microstructured environments. In microfluidic devices or close-to-surface interfaces, the behavior of microions can differ from bulk due to strong confinement, high surface-to-volume ratios, and interfacial effects, influencing screening, transport, and electrostatic interactions.

Terminology notes: microion is not a universally standardized term across all literature. When encountered, it is best interpreted from the surrounding context, particularly whether the discussion concerns microelectrode techniques, microfluidics, or microscopic electrolyte behavior.

See also: ion, electrolyte, microiontophoresis, microfluidics, electrical double layer.