Elaine, Consider side scatter as a selection parameter . . . the AU particles should have a high SS signal to start, and the addition of material may increase (hopefully) in a proportional manner. I can't predict what the distribution will look like, and a (very) quick search revealed no references. But I can recall this type of analysis being done (in the "early days" of flow . . .). Certainly, it parallels the development/analysis of the beads we run all the time. Regarding their size . . . 100 nm approaches the threshold of resolution for most flow cytometers. I've run 50 nm particles, but had to rely on fluorescence to detect these initially. I found 100 nm particles with -out fluorescence, but it's not easy. Uniformity is key . . . if your particles vary dramatically, you'll have a harder time making sense of the data. Also, smaller particles behave erratically in a fluid stream, not as predictably as do "larger" particles, like cells. This makes sorting even more difficult, but I'd worry about that later. Going back to the reference of bead development . . . can you modify the layering material to include a fluorescent dye? You could then monitor the accumulation be fluorescence increase. Finally, considering your need to separate these by size . . . in my very cursory search, I did see a reference for electrophoretic separation of microparticles - - perhaps that's a way to go. MAK. -- Mark A. KuKuruga, Managing Director University of Michigan Flow Core 7416 CCGC 0946 (734) 647-3216, fax (734) 936-7376 kukuru@umich.edu >>> Elaine Kunze <mek4@psu.edu> 03/26/01 03:43PM >>> I am sending this again because the replies I have gotten are all talking about LARGE particles. These are tiny, little 100 nanometer particles. Now, are there any suggestions? What I sent originally: One of my reseachers is having difficulty separating a mixture of glass spheres and glass-coated, colloidal Au, core-shell particles. The free glass spheres nucleate and grow under the reaction conditions for the growth of the core-shell particle. The typical ratio of the free glass spheres to core-shell structures is ~100:1. The size of the core-shell particles is between 100-115 nm in diameter. The free silica particles are only slightly smaller in diameter (by about 5-10 nm). He has tried gradient separation and gradient centrifugation with a high MW dextran and low MW PEG, but has not come across appropriate conditions for separation. He is currently exploring the use of flow cytometry. Any suggestions are greatly appreciated? **************************************************************************** Elaine Kunze Flow Cytometry.....Image Analysis... Life Sciences Consortium 8B Althouse Laboratory (814-863-2762) Penn State University University Park, PA 16802
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