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Mark, your analysis of FACScalibur vs. XL is not completely accurate. The XL
can use Cy5PE together with PE and FITC. Cy5PE is actually even more sensitive
than PE for low density antigens. Thus, both machines can do 2 colors of high
sensitivity. The FACScalibur can't do Cy5PE and APC together very well, because
of the substantial cross-excitation. (Yes, I know that applications can be
designed where this "feature" will not hinder the experiment).
By the way, it is not energy transfer which is relevant to the dyes FITC, PE,
PerCP, and APC, but quantum efficiency. Energy transfer refers to tandem dyes
such as Cy5PE. Also, it is not appropriate to compare emission intensity at
"equivalent excitation" intensity for APC and the other dyes, since they are
different lasers. The real comparison is how bright a reagent is compared to
autofluorescence--a ratio which varies with excitation intensity but can be
optimized for some of the dyes.
And while the FACScalibur can sort, this capability is designed primarily for
rare-cell applications and is not suitable for most sorting applications; this
advantage over the XL may not be significant to may laboratories.
Please note that I am not addressing the relative merits of the two
instruments.
mr
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