wmelchior at ntet.nctr.fda.gov
wmelchior at ntet.nctr.fda.gov
Thu Mar 4 17:19:54 EST 1993
In article <1993Mar4.141316.14819 at alw.nih.gov>, jeffs at elsie.nci.nih.gov
(Jeffrey Alan Silverman) writes:
> We are currently considering purchasing either a phosphoimager or a betascope
> from either Molecular Dynamics, Fuji or Betagen. So I would like to know if
> anyone out there has any experience with these instruments and has
> any insight.
> I am particularly interested in comments on sensitivity, resolution and
> reproducibility. Speed and reliability are important. Also does anyone use
> them on a network to port the data to a remote terminal to do their data
> analysis? Any sequence reading? How about lifespan of the screens?
> Thanks for your help
> Jeff Silverman
> Jeffs at elsie.nci.nih.gov
While I haven't personally used these, I'm somewhat familiar with them,
since there are both Molecular Dynamics and Betagen instruments in my
building. The Betagen is in a different group, however, so I don't know
what the experience with it has been.
The MD and Fuji systems work by exposing a ceramic material (very much like
an Xray intensifying screen) to the blot, gel, etc., in a metal cassette.
A number of different exposures can thus be made simultaneously. The
machine is just used for scanning the pattern off of the (reusable)
screens. I think MD claims about a 6-fold increase in sensitivity over
film (without chilling), and results here suggest that that's a reasonable
estimate. Another BIG advantage over film is that results are linear over
many orders of magnitude, so one can expose different levels of
readiocactivity at the same time. The machine can scan at two levels of
resolution, but the workers here use only the coarser setting. I've seen a
35S sequencing gel scanned at "coarse", and I thought it looked pretty good.
There have been no problems yet with the screens; with careful handling,
I think they're supposed to last indefinitely.
The Betagen works by a completely different method: The item to be scanned
is put into the machine and read by detection of ionization in a chamber.
It differs from the old scanners in that each individual decay can be
localized. The Betagen probably has some of the same advantages as the
other machines; for instance, I would expect that the results would be
linear over large ranges. And it has the possible advantage that the
results can be displayed as they are accumulating. However, if one needs
an overnight exposure, for instance, the machine can't be used for anything
else during that time. And one would probably not want to scan items with
quite different levels of readioactivity at the same time. Another
disadvantage is that the machine can be contaminated fairly easily. (It's
happened here.) The MD and Fuji mahines, on the other hand, never see
radioactivity, only the screens.
The analysis program with the MD machine is fairly powerful, allowing
visualization, quantitation of spots, etc; I can't comment at all about the
others, but imagine they're similar. The MD software has a simple sequence
reading utility, allowing rapid entry of data with the mouse; it's not
automatic, however. Data can be transferred here to PCs, but we've not had
the capability long, so we don't have a lot of experience. Once people get
used to the requisite commands, it will probably be routine. The files,
being graphics, are BIG.
Finally, Molecular Dynamics has been helpful over the phone. It's nice to
know that help is usually not far away.
I have no connection with any of the companies. The people in my group use
the PhoshpoImager, perhaps biasing my opinion; but they're happy with it,
and it looks to me like it has important advantages over the Betagen. I
have no information on the Fuji. (Last year, Ambis also had a machine, and
Pharmacia announced one.)
As you're aware, you're talking mucho $$ for any of these.
Views expressed are not necessarily those of NCTR, its sponsoring agencies,
or the United States government.
Bill Melchior || MISSING LINK
National Center for Toxicological Research || Man's a kind
Jefferson, AR 72079 || of Missing Link,
(501) 543-7206 || fondly thinking
|| he can think.
WMELCHIOR at NTET.NCTR.FDA.GOV || from Grooks, by Piet Hein
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