filters vs gratings

David C.Fritzinger dfritzin at nospam.hotmail.nospam.com
Mon Apr 1 23:03:27 EST 2002


In article <a8aajr$rol$1 at mercury.hgmp.mrc.ac.uk>, MES
<walkmori at sover.net> wrote:

> Thank you for your input.
>
> A few more questions if you don't mind.
>
> 1. Is there a rule of thumb on minimum dye-stokes-shift a grating-based
> instrument can handle?

I'm afraid I don't know the answer to this one. However, I would guess
that a grating based machine would be better with two dyes that overlap
alot in their spectra, since you have infinite adjustability in the
cutoff points, though the slope of the cutoff curve may or may not be
as steep.
>
> 2. Is there a rule of thumb on minimum sample volume a grating based
> instrument can handle?

This question doesn't really make sense. For a gel based machine, it is
the amount of DNA/lane that is important, not the sample volume. You
generally load ~5 microliters/lane IIRC (it has been a while since I've
used a 377). For a capillary based sequencer, such as the ABI 3700 or a
MegaBace, you need ~10 microliters of sample volume (or more), but
again the important factor is the amount of DNA in your samples, since
signal is proportional to quantity of DNA sequenced.
>
> 3. Is there a drop off in demand for sequencers?

Again, I don't really know. I would suspect the demand is dropping, but
there is still plenty of sequencing to be done. And, if someone came up
with a real advance in sequencing technology, making it cheaper or
faster, their machine would still sell well.

Hope this helps,

Dave Fritzinger
>
>
>
> "David C. Fritzinger" <dfritzin at nospam.hotmail.nospam.com> wrote in message
> news:a898qp$5rl$1 at mercury.hgmp.mrc.ac.uk...
> > In article <a87bvg$hmo$1 at mercury.hgmp.mrc.ac.uk>, MES
> > <walkmori at sover.net> wrote:
> >
> > > Recently I have been told that companies like Applied Biosystems are
> moving
> > > from optical filters to gratings for spectral filtering.
> > >
> > > Is it possible to sequence with a grating based instrument?
> > >
> > > Is the near band rejection high enough?
> > >
> > > Is the optical energy throughput high enough?
> >
> > Actually, I believe that, ever since the 377, ABI has been using
> > gratings for spectral filtering. That's why they call their instruments
> > "Prism". It is also why it is so simple to use a number of different
> > dye sets in ABI insturments.
> >
> > I believe the answer to all your questions are yes. Both types of
> > insturments have advantages. I believe the MD machines, which use
> > filters and a confocal microscope for detection are more sensitive,
> > while ABIs insturments are easier to set up for different dye sets, and
> > easier to use for more than 4 dyes.
> >
> > Hope this helps.
> >
> > Dave Fritzinger
> > >
> > >
> > > ---
> >
> > ---
> >
>
>
> ---

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