Re: fluorochromes and x-rays

From:"J. A. Kiernan"

John Baker wrote:
> 1. How, if at all, do x-rays affect fluorochome labels?
> 2. What is the mechanism that causes fluorochromes to lose their
>    excitability when exposed to normal spectrum light?

I don't know the answer to the 1st question, but for the
second it is surely that pretty well all fluorochromes
absorb visible light. Some have their maxima in the blue
(eg fluorescein) or green (eg rhodamines). For those that
are excited optimally by UV, the absorption peak is commonly
in the near UV - not far from visible violet - and within the
spectrum of regular daylight. Some UV-excited ones are yellow,
indicating that a significant chunk of the absorption spectrum
is in violet-blue range.  If a fluorochrome were to absorb only
in the far UV, and not absorb any ordinary light, it wouldn't
lose its excitability in daylight. To undergo a photochemical
reaction, a substance must first absorb some light.

Good luick with the X-ray question.

John A. Kiernan
Department of Anatomy and Cell Biology
The University of Western Ontario
London,   Canada   N6A 5C1

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