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Fluo-4, pentapotassium salt

Fluo-4, pentapotassium is membrane-impermeant calcium indicator. It can be loaded into cells via microinjection or scrape loading.

Product Attributes


Calcium indicators

Cell permeability

Membrane impermeant

Indicator type



494/516 nm

Catalog #
0.5 mg
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Product Description

Fluo-4 is an analog of Fluo-3 with the two chlorine substituents replaced by fluorines, which results in increased fluorescence excitation at 488 nm that gives higher fluorescence signal. Fluo-4 has its absorption maximum at 494 nm, thus making it excitable by the argon-ion laser. Fluo-4 is essentially nonfluorescent without Ca2+ present, but the fluorescence increases at least 100 times on Ca2+ binding. Also, because Fluo-4 binds Ca2+ more weakly (higher Kd) than do fura-2 and indo-1, it is more useful for measuring high transient Ca2+ concentration during Ca2+ spikes.

Fluo-4, pentapotassium is membrane-impermeant, but can be loaded into cells via microinjection or scrape loading. We also offer a membrane-permeant version, Fluo-4 AM Ester (catalog number 50018).

  • Kd: ~335 nM
  • λExEm (low or high [Ca2+]) = 494/516 nm
  • ε (494 nm) = 82,000 M-1 cm-1
  • Orange solid soluble in DMSO and water (pH >6)
  • Store at 4°C. Protect from light, especially when in solution
  • C36H25F2K5N2O13
  • MW: 927.09



1. Gee, K.R., et al. Cell Calcium. 27, 97(2000).


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