Abstract— 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 thc 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 × 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.
|Number of pages||5|
|Journal||Photochemistry and Photobiology|
|State||Published - Sep 1993|