Advice on video of Ethidium Bromide gels needed.
rosswhet at forbt2.nrrc.ncsu.edu
Thu Dec 10 16:17:15 EST 1992
In response to several requests for further information about my experiences with various
video imaging systems, I am posting a more detailed description of the systems I have seen.
First, the usual disclaimers:
This represents a summary of my personal experiences with demonstrations of various imaging
systems, and should not be taken as any reflection on the suitability of these systems for
purposes other than that of imaging ethidium-bromide stained DNA in agarose gels on a
UV transilluminator. This is not an exhaustive list of manufacturers or distributors of
imaging systems, and failure to mention a system should not be interpreted as anything but
a complete lack of information in my hands about that system.
I have no connection with any of the companies mentioned nor with any
other company that manufactures or distributes such imaging systems; my only relationship
with these companies is that of potential customer. The order in which the imaging systems
are mentioned below reflects only the order in which the sales literature is stacked in a
pile on my desk, not any ranking of suitability or lack thereof. The prices listed are
approximations, largely given from memory, and should not be taken too literally. They are
listed only to give some feeling for the relative expense of different ways of approaching
the imaging problem.
GelPrint 2000i unit, cost about $10,000
includes camera with Peltier cooling to reduce noise, lens and bandpass filter, dedicated
digitizer with 3.5" floppy disk drive, monitor and thermal printer. The system includes an
integrator with the ability to vary the exposure time from .1 to 99 seconds to improve
sensitivity. I have not seen a demo of this unit, but of the precursor to it which was
less advanced and not entirely satisfactory to me. The current version has been improved
to deal with all the issues that were problems in the original. One nice feature of this one
is the disk drive; the images can be saved directly to floppies for later analysis by any
program (including BioPhotonics') that can work with TIFF, PCX, or HP LaserJet files on either
a Mac or PC.
Eagle Eye unit, cost about $9,000
includes camera, lens and bandpass filter, integrator, monitor, printer, and a big wood box
to put it all in so it doesn't need to be in a darkroom. No provision for saving the files
(long term) in the basic system; an optional storage device costs a few thousand more. This
system has the integrator to give higher sensitivity, and it works fine. Integrating 10
frames is usually enough for a normal gel, but if you want to look at very very faint signals,
you can turn it up to 99 frames and see the DNA that is left in a gel after it has been
blotted by capillary transfer overnight. No software included or (as far as I know) available;
the system is entirely analog-based and does not give a digitized image file at any point.
"The Imager", quoted price $12,900
Similar to BioPhotonics unit in that it includes a 3.5" floppy drive and can save TIFF files
of the digitized image for later analysis. Price also includes Peltier-cooled camera, lens
and filter, controller/digitizer, monitor and printer. I have not seen a demo of this one,
and don't know if it includes a digitizer or not, nor how suitable the sensitivity is for
imaging DNA in gels.
Gel Documentation System GDS 2000, quoted price $6,000
includes cooled camera, lens and filter, printer and monitor. No mention of integrator in
sales literature, no demo to verify sensitivity. Accompanying software available for PCs
to analyze digitized images.
There are some other systems that are intended for high-end image analysis applications that
include image acquisition hardware as well, but prices for those units start at about $20,000
and go up. This is a lot more than I want to pay for an alternative to Polaroid film.
Imaging systems can also be assembled from components purchased independently, which is the
approach I am working toward now. High-sensitivity cameras are available from several
manufacturers and distributors; the two I have checked on are Dage-MTI and Motion Analysis
Inc. They both use the same chip (the Sony XC-77 for hardware buffs) and build on
additional goodies to improve the sensitivity and control over image quality. As I understand
it, Dage actually builds their camera, while Motion Analysis modifies a camera made by Pulnix.
In any event, the price of the Dage camera is about $4000, while the Motion Analysis unit is
about $2700; the two cameras seem to be very similar in capabilities and functions.
A zoom lens for either of these cameras costs about $250, available from the camera vendors.
The zoom feature is nice because it means the camera need not be moved in order to have the
gel image fill the field of view.
A 595nm bandpass filter (required to eliminate the UV and IR output of the transilluminator) is
about $200 to $250, available from Corion or Dell Optics.
A 9" or 10" black and white monitor can be had for about $250, and a thermal printer is $1000
to $1500 depending on what size print you like. Both are available from local video suppliers.
A system consisting of the Motion Analysis camera, Fujinon 12.5-75 zoom lens, bandpass filter,
9" monitor and 3"x4" printer could be assembled for about $4500, even allowing for some differences
in pricing. This should be a self-sufficient system for imaging gels, with adequate but not
spectacular sensitivity. The camera is only just able to image gels with the gain turned up
all the way, so any deficiency in the gel for any reason would means problems with the imaging
system. The pulnix camera has integration circuitry built into the camera unit, but taking
advantage of that option requires building a trigger circuit to cue a frame grabber to capture
the output of the integration circuit. We are looking into having this circuitry built to
interact with our DataTranslation Quick Capture card in a Mac IIci running the Image
software package from NIH. This should give us a complete system, with ample sensitivity
for all but the most demanding applications.
In the final analysis, the system that is right for any particular laboratory really depends
on the kinds of things that laboratory does, and every lab has slightly different requirements.
If you don't need computer analysis of image files, one of the systems that works entirely
with analog images will probably give you the best price to performance ratio. If you do need
computer analysis, look at the free NIH software before you pay $2000 to $3000 for a commercial
package, especially if you prefer the Mac interface. The latest version of Image is available
from alw.nih.gov, in directory pub/image.
Research Assistant Professor
Forest Biotechnology Group
North Carolina State University
Raleigh, North Carolina 27695-8008 USA
telephone or fax (919)515-7801
e-mail rosswhet at unity.ncsu.edu
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