Indo-1 is a popular dye that is used as a ratiometric calcium indicator similar to

Fura-2 Fura-2, an aminopolycarboxylic acid, is a ratiometric fluorescent dye which binds to free intracellular calcium. It was the first widely used dye for calcium imaging, and remains very popular. Fura-2 is excited at 340 nm and 380 nm of ...

. In contrast to Fura-2, Indo-1 has a dual emissions peak and a single excitation. The main emission peak in calcium-free solution is 475 nm while in the presence of

calcium Calcium is a chemical element; it has symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to it ...

the emission is shifted to 400 nm. It is widely used in

flow cytometry Flow cytometry (FC) is a technique used to detect and measure the physical and chemical characteristics of a population of cells or particles. In this process, a sample containing cells or particles is suspended in a fluid and injected into the ...

and laser scanning microscopy, due to its single excitation property. However, its use for

confocal microscopy Confocal microscopy, most frequently confocal laser scanning microscopy (CLSM) or laser scanning confocal microscopy (LSCM), is an optical imaging technique for increasing optical resolution and contrast (vision), contrast of a micrograph by me ...

is limited due to its photo-instability caused by

photobleaching In optics, photobleaching (sometimes termed fading) is the photochemical alteration of a dye or a fluorophore molecule such that it is permanently unable to fluoresce. This is caused by cleaving of covalent bonds or non-specific reactions between ...

. Indo-1 is also able to keep possession of its ratiometric emission, dissimilar to Fura-2. The penta potassium salt is commercially available and preferred to the free acid because of its higher solubility in water. While Indo-1 is not cell permeable the penta acetoxymethyl ester Indo-1 AM enters the cell where it is cleaved by intracellular esterases to Indo-1. The synthesis and properties of Indo-1 were presented in 1985 by the group of Roger Y Tsien. In intact heart muscle, Indo-1, in combination with bioluminescent protein aequorin, can be utilized as a tool to distinguish between the internal and exterior inotropic regulation processes.{{Cite journal , last=Endoh , first=Masao , date=2006 , title=Signal Transduction and Ca2+ Signaling in Intact Myocardium , url=http://www.jstage.jst.go.jp/article/jphs/100/5/100_5_525/_article , journal=Journal of Pharmacological Sciences , language=en , volume=100 , issue=5 , pages=525–537 , doi=10.1254/jphs.CPJ06009X , issn=1347-8613

References

Biochemistry methods Cell imaging Chelating agents Fluorescent dyes Glycol ethers Indoles