How calcium indicators work

In the last two decades, imaging of fluorescent indicators specific for Ca(2+) has revealed its often spectacular spatial dynamics, such as rhythmic oscillations or standing gradients, within single groups or individual cells, in unprecedented detail. This short review describes how the more widely used indicators work. The currently used Ca(2+) indicators have a modular design consisting of a metal-binding site (or sensor) coupled in some way to a fluorescent dye. Combining different sensors with different dyes results in numerous indicators suited to a wide range of experiments and equipment.