>Dear members,
>
>        I am trying to deliver light (UV and visible) to a limited area of a
>cell prep in order to study rapid responses to this stimulus (eg.
>intracellular calcium levels). The set-up I am imagining is having a laser
>source (the ideal for us is a tunable one, in order to be able to examine
>responses to different wavelengths) and a fiber optic to carry the light to
>the vicinity of the cell (I guess a micromanipulator would be necessary to
>target the cell). Does anybody know which is the smallest spot of
>illumination possible nowadays? Will I be able to stimulate a single cell, a
>group of cells, an area on the surface of a cell? Also, is there an
>alternative to this (to avoid the obvious expense)? (I am sure all these are
>also questions you will like, Johannes...are you there?)
>


Maybe I haven't understood your problem correctly, but couldn't you use an
"ordinary" fluorescence microscope? By closing the iris you would be able
to stimulate single cells dependent on how dense they are grown. With a
confocal laserscanning microscope you should be able to iluminate much
smaller areas. The smallest possible square on the Leica TCS 4D System is
about 5 microns. However I never tested this, it does not make much sense
for microscopy in terms of resolution. If you scan a certain area over and
over again and then change to a lower resolution, you can nicely see that
the fading is limited to a square.

Of course you would be limited in both cases with the available
wavelengths, either by the laser or by the available filter set. Also, you
probably would have stray light to neighboring areas, but you probably
cannot avoid that with any setting.


Hope this helps,

Steffen

-- -------------------------------------------------------------
Dr. Steffen Dietzel
Zentrum fuer molekulare Biologie Heidelberg (ZMBH)
University of Heidelberg
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