Figure 6.

Probes for sensing ion fluctuations. a) Reporter Fura‐2 binds Ca²⁺, thereby changing its excitation properties for live‐cell Ca²⁺ imaging. b) Fluo‐4, AM and Rhod‐2 are shown for live‐cell Ca²⁺ imaging. Acetoxymethoxy (AM) esters can be used to mask the charged carboxylates for intracellular delivery, where esterase liberated the Ca²⁺ sensing unit (cf. Fluo‐4). c) Example of intensiometric behaviour. Upon increasing Ca²⁺ concentration, an increase in fluorescence can be detected by a single emission band. d) Example for a ratiometric behaviour. Two emission bands change diametrically upon pH changes. e) SNARF‐1 is a ratiometric pH sensor.