Lambert Instruments

For ion imaging, several (fluorescent) indicators are available that have a change in quantum yield upon ion binding. This can mean that they can emit photons with different energy, thus different emission wavelength. Also it can mean that they can have a change in fluorescence lifetime. Therefore, there are two ways in which ion imaging can be done by use of indicators: the ratiometric method and the FLIM method.
Another way in which ion imaging is done, is by using FRET-based indicators that change their conformation upon ion binding. Upon the conformationl change the FRET efficiency changes, which is used as indicator for the ion concentration. E.g., cameleons are genetically-encoded fluorescent indicators for Ca2+ based on green fluorescent protein variants and calmodulin (CaM):

Calcium (Ca2+) imaging
Calcium is important for signal transduction pathways.

Proton (H+) (pH) imaging
The intracellular proton concentration (pH), as well as intracellular calcium, is important in the regulation of cellular functions including growth, differentiation, motility, exocytosis and endocytosis. To learn more about this, measurements of the intracellular pH of resting cells can be done and the pH fluctuations inside cells after environmental perturbations can be followed. An example:

Zinc (Zn2+) imaging
Zinc is involved in enzyme catalysis, protein structure, protein-protein interactions, and protein-oligonucleotide interactions. Zinc interacts with extracellular binding sites, which are likely to include binding sites involved in the subsequent translocation of this ion to the cell interior. Inside the cell, Zinc binds to cytosolic and organelle binding sites or is taken up by intracellular organelles.

Sodium (Na+) imaging
Sodium is important in the signal transduction in the central nerve system.

Magnesium (Mg2+) imaging
Many enzymes (like kinases) require the presence of magnesium ions for their catalytic action, especially enzymes utilising ATP.

Chloride (Cl-) imaging
Chloride plays a role in the central nervous system.

Potassium (K+)
Potassium plays a role in cell growth and cell viability.

Indicators for ion imaging by FLIM:
BCECF (pH)
Bis-BTC (heavy metals)
Calcium-crimson (Calcium, orange excitation)
Calcium-green (Calcium, blue excitation)
Carboxyfluorescein (pH)
Carboxy-SNAFL-1 (pH)
Carboxy-SNAFL-2 (cytosol pH)
DM-NERF dextrans (lysosoml pH)
Fluo-3 (Calcium)
Fura-2 (Calcium)
LysoSensor DND-160 (lysosomal pH)
LysoSensor probe (pH)
Magnesium-green (Magnesium)
Mag-quin-1 (Magnesium)
Mag-quin-2 (Magnesium)
MQAE (Chloride)
Newport Green DCF (Zinc)
OG-514 carboxylic acid dextrans (lysosoml pH)
PBFI (Potassium)
Quin-2 (Calcium, blue excitation)
SPQ (Chloride)