Thursday, October 4, 2007

Using a green laser pointer on a flow cytometer!

Well, the folks at Los Alamos National Labs ( never cease to amaze me.  They outfitted one of their slow flow flow cytometers with an ordinary $160 green laser pointer (2.4mW at 532nm), and it works...well, sort or. 

Don't go throwing away your 200mW DPSS 532nm lasers just yet.  I don't know if you caught this, but the "garage-built" flow cytometer this laser is mounted on is a SLOOOOOOW flow cytometer.  For comparison sake, one of the fastest flow cyotometers, the MoFlo ( has an illumination time frame of about 1.2us, the slow flow instrument has to have an illumination time frame of at least 25us (~20-fold increase).  Most conventional bench-top cytometers are somewhere between 1us and 4us windows.  From a practical standpoint, the larger the illumination window, the slower your event rate has to be in order to avoid having multiple cells in the illumination area at one point.  So, if you typically run at max 20,000 cells/second on a conventional flow cytometer, you're stuck at 1000 cells/second on the slow flow cytometer.  The nice thing about the slow flow instrument is that since there is a longer exposure time to the laser light, fluorochromes can be excited multiple times, and the fluorescence output increases dramatically.  This is why they can report detection threshold values of ~52 MESF in the PE channel on this instrument.  Not bad.  Although marketing materials from commercial vendors publish outrageous values for the detection threshold, I've never really seen any much below 50MESF, so I'd have to say this is probably more sesitive than any instrument around.  The practical implications of such an instrument, as you could imagine, is the low cost of production for such a cytometer.  Lasers on any other instrument are $10K or more, but for a $160 laser and great sensitivity, I'd be willing to run at a slow rate.  Their findings were published in Cytometry Part A. Habbersett, R. C., Evaluation of a Green Laser Pointer for Flow Cytometry., Cytometry Part A, Volume 71A, Issue 10, p809-817.