The use of fluorescent dyes is the most popular tool for measuring ion properties in living cells. Calcium, magnesium, sodium, and similar species that do not naturally fluoresce can be measured indirectly by complexing them with fluorescent molecules. The use of probes, which fluoresce at one wavelength when unbound, and at a different wavelength when bound to an ion, allows the quantification of the ion level.

Fluorescence has also become popular as an alternative to radiolabeling of peptides. Whereas labeling of peptides with a radioactive compound relies on the introduction of a radio-labeled amino acid as part of the natural structure of the peptide, fluorescent tags are introduced as an additional group to the molecule.

The use of fluorescent dyes allows the detection of minute amounts of the target molecule within a mixture of many other molecules. In combination with light microscopic techniques like confocal laser...