Ion flux assays are cell-based functional assays. They trace ionic flux through channels by radioisotopes, or detect ionic flux using highly sensitive flame atomic absorption spectrometers (AAS) or using fluorescence ion-specific probes/biosensors. Ion flux assays use a radioactive species in combination with a scintillation counter or use a tracer ion measured by atomic absorption/emission spectrometry.

In the 1980’s the development of ion-selective fluorescent dye-based indicators revolutionized the measurement of ion flux. These indicators improved the ease of use, as well as spatial and temporal resolution of ion flux measurements. More recently, the use of automated flame photometry-based ion flux assays has been proven effective as an alternative to fluorescent and radionuclide-based techniques for some ion channel assays.