Posted by
Christian Wilms on
URL: http://confocal-microscopy-list.275.s1.nabble.com/Ratiometric-measurements-for-multiphoton-microscopy-tp7585091p7585102.html
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Hi Mark,
>Any idea what is the cause of the difference between the measurements you cite and the
conclusions of Szmacinski et al (Photochem Photobiol. 1993 Sep;58(3):341-5): "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. “?
I can only hazard a guess, as it is surprising that the two reported values are so different.
Reading the Szmacinski paper, they seem to have estimated the cross-section by
comparison with a standard. In constrast Xu and Webb
(
http://www.pnas.org/content/93/20/10763.long) seem to have measured it directly. But, as
the former estimation is common methodology, I doubt that alone can explain the
difference.
Best, Chris