you can be worried about some particles grinding down the shear valves employed in some instruments and we had that problem when measuring sewage (in the original skatron prototype) causing leakage's. Some iron particles are sharp crystals, so I would expect similar problems Regarding magnetic sorting I had my best successes with the Miltenyi beads as the dynabeads we tried shedded their load with the antibody. Regards Gerhard -----Original Message----- From: Steve G. Hilliard [SMTP:steve@habanero.cb.uga.edu] Sent: Wednesday, November 15, 2000 8:09 PM To: Cytometry Mailing List Subject: magnetic beads and valves? Hi folks, I just recieved a question regarding work we published using immunomagnetic beads for detection of E. coli (Journal of Food Protection (1998) V61, No. 7, pp812-816.) Our approach was to incubate food samples with ~5u magnetic beads bearing an Ab against E. coli, and then to sandwich label w/ another fluorescent Ab, also against E. coli. The machine then analyzes beads, not cells, like the bead assays in vogue today. The reader would like to employ the same technique, but concerns have been raised regarding the effect of magnetic beads accumulating in and damaging the "magnetic valves" (?) in their flow cytometer. I don't expect it to be a problem, since there [should] be little or no sample carryover or bead retention, but I'll admit that I never considered it before. Has anyone had any bad experiences, or heard of problems of this type? Aren't most of these beads paramagnetic, ie attracted to magnetic fields, but not intrinsically magnetic? Even if all the pinch valves were controlled by electromagnetic actuators, and the beads were attracted to them, how would they damage the valves? Anyone ever heard of such a thing? Steve +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Steve G. Hilliard (706) 542-9474 University of Georgia Cell Analysis Facility flowman@uga.edu http://floweb.cb.uga.edu/
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