Re: Cellular Astronomy

Mark Coles wrote:

>	  I have become interested in the low cost high sensitivity 
> integrating video cameras for the detection of fluorescent signals 
> (approaching 0.00005 lux).  For those interested in the stars see Sky and 
> Telescope December 2003 (Deep-sky Imaging with Integrating Video 
> Cameras).  My interest is due to their price aprox $250-800 depending on 
> the model, and very low noise levels.  My question for anyone is have 
> they tried them to analyze fluorescent signals on a microscope and is 
> there an inexpensive method of acquiring the images onto a PC or Mac.

The article lists five relatively inexpensive CCD cameras. The Astrovid 
StellaCam-EX (www.astrovid.com), ITE DeepSkyPro EX (www.iteastronomy.com), 
Mintron MTV-12V1-EX  and
Watec WAT-120N (www.mintron.co.uk) are all in the US$600 to $900 range, and 
most use a Sony ICX248AL monochrome image sensor. None have options for 
either electronic (Peltier) or water cooling, and most appear to have only 
analog video output, requiring a frame grabber and software to be used with 
a telescope (or microscope). The Polaris DX-8263SL (www.polarisusa.com) is 
only $295, but has a color CCD. Color CCDs are monochrome CCDs with an 
array of microfilters over the elements; one line is green-red-green and 
the next is green-blue-green, etc.; they are less sensitive than CCDs 
without the filters and, more to the point, it is difficult if not 
impossible to use them for quantitative measurements.

I and a number of other people I know have settled on the Model ST-7XMEI 
camera from Santa Barbara Instrument Group (SBIG) (Santa Barbara, CA, 
www.sbig.com), which costs $1495. It uses a Kodak microlensed KAF-0402ME 
CCD chip. The chip has approximately the same number of pixels as the Sony 
chip (actually a few more, 768 x 512), and the wells (pixels) are about the 
same size, 9 µm square. However, the Kodak chip has an array of microlenses 
over the chip, which improve illumination, and can achieve a peak quantum 
efficiency of 77%, substantially higher than that of the Sony chip. used in 
the  The Kodak chip has a capacity of 100,000 electrons/well, allowing a 
measurement dynamic range of just under 4 decades for each pixel in a 
single exposure. The SBIG camera includes Peltier cooling circuitry, 
transmits digital data to a PC via a USB cable, and comes with image 
capture software that allows for some image manipulation and also can store 
files in standard formats such as TIFF.

The SBIG camera has substantially lower noise levels than the cameras 
mentioned in the Sky and Telescope article. Unger et al (Unger M, Kartalov 
E, Chiu CS, Lester HA, Quake SR: Single-molecule fluorescence observed with 
mercury lamp illumination. Biotechniques. 1999; 27:1008-14) used an earlier 
version of the SBIG ST-7 camera, with a less sensitive CCD (and a price 
twice that of the current version), to detect fluorescence from single 
molecules of FITC, rhodamine dyes, and GFP, so sensitivity is not an issue 
here; The samples were examined on cleaned glass coverslips; background 
fluorescence from glass slides would prevent detection of fewer than a few 
thousand molecules of dye or GFP (you may want to use quartz slides or 
black polycarbonate or aluminum oxide membranes as substrates for your cells).

To use the SBIG camera with a microscope, you need to order it with a C 
mount rather than the customary T mount. Video couplers, i.e., adapters 
that allow mounting the camera on various fluorescence microscopes, are 
available from Thales Optem (www.thales-optem.com) for $400-$500, but you 
might be able to get away without one if your microscope has an appropriate 
camera port.

Yes, this may cost you closer to US$2000 than US$800, but you will be on 
the air collecting data within an hour or two of receiving the parts, and 
you can't beat that. And the $800 will quickly creep up by several hundred 
dollars because you will still need a frame grabber, software, and a video 
coupler, so you're really taking about $2000 vs. $1500. The decision is a 
no-brainer.

There isn't Mac acquisition software for the SBIG camera, as far as I know, 
but there's nothing stopping you from processing the images on a Mac after 
you acquire them on a PC.

I'll supply the details about using LED illumination elsewhere, perhaps in 
the First Edition of "Practical Cellular Astronomy", but probably sooner 
than that.

-Howard