Calcium-dependent fluorescence lifetimes of Indo-1 for one- and two-photon excitation of fluorescence

Photochem Photobiol. 1993 Sep;58(3):341-5. doi: 10.1111/j.1751-1097.1993.tb09571.x.


We characterized the fluorescence intensity decays of Indo-1, which is commonly used as an emission wavelength-ratiometric calcium probe. The apparent lifetime of the long-wavelength side of the emission of Indo-1 is dependent on Ca2+. This long-wavelength emission displays the characteristics of an excited-state reaction, that is, a negative preexponential component in the multiexponential analysis. The emission spectra and lifetime of Indo-1 appear to be identical for one-photon and two-photon excitation at 351 and 702 mn, respectively, suggesting that the relative one- and two-photon cross sections are similar for the calcium-free and calcium-bound forms of Indo-1. Also, the two-photon cross section of Indo-1 is relatively high, about 4 x 10(-49) cm4 s/photon molecule at 690 nm for both the calcium-free and calcium-bound forms. Hence, Indo-1 can be used for calcium imaging based on one- or two-photon excitation, using either emission wavelength ratios or lifetime imaging methods.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Calcium / chemistry*
  • Fluorescence*
  • Fluorescent Dyes / chemistry*
  • Indoles / chemistry*
  • Photons


  • Fluorescent Dyes
  • Indoles
  • indo-1
  • Calcium