do you plan to build your own DLS setup or to use a commercial system?
yes, in principle you can use DLS, if the particles are not very large (more than a few hundred nanometers) or very small (less than a few nanometers), so that the answer "yes" or "not" depends on the molecular weight of your dextran.
Only you have to be aware are that the "size " you obtain from DLS is the hydrodynamic radius, i.e, something that depends on the drag force that particles experience traveling through the viscous liquid in which they are dispersed (water in this case? ). This force, for a macromolecule depends on its conformation, and the radius isthat of an "equivalent sphere " that feels the same drag force, so that its relation to the "real size" of the macromolecules is different if the molecules is a short rod-like oligomer, a random coil, a compact globular protein etc.
A good book on this is the Berne and Pecora classic "Dynamic light scattering: with applications to chemistry, biology, and physics"
Hi Alessia,
I agree with Prof. Bordi. you will get the diameter of an equivalent sphere.
this "size" value may be quite meaningless depending on the shape of your particles. therefore it may be useful to do a reference measurement of a small sample with SEM or TEM in order to see the actual shape and to allow an evaluation of the DLS results
well, this was my idea! I got a distribution of a sample which I studied by FESEM and now I wanted to compare it with the results of DLS.
that's the right approach. should your commercial DLS give strange results, you're welcome to send a sample and we can test it with a more sophisticated (custom made) setup.
With DLS you get a diffusion coefficient. There are literature results lining D to molecular weight using calibrated materials, so you can get out a molecular weight. The problem you face is that typical dextrans are polydisperse so the transition is challenging. I seem to recalll, however, that people have fractionated material and then did DLS on fractions. For example, iirc from 40 years ago, Kunitake and research advisor at UCLA did ultracentrifuge, transported the transparent tube to a DLS unit, and did DLS at a series of heights. One might also imagine doing this on electrophoresis (not dextran,clearly) or column output, perhaps with some need to reconcentrate at the output of the fractionation column.
With DLS you get a diffusion coefficient. There are literature results lining D to molecular weight using calibrated materials, so you can get out a molecular weight. The problem you face is that typical dextrans are polydisperse so the transition is challenging. I seem to recall, however, that people have fractionated material and then did DLS on fractions. For example, iirc from 40 years ago, Kunitake and research advisor at UCLA did ultracentrifuge, transported the transparent tube to a DLS unit, and did DLS at a series of heights. One might also imagine doing this on electrophoresis (not dextran, clearly) or column output, perhaps with some need to reconcentrate at the output of the fractionation column.
With DLS you get a diffusion coefficient. There are literature results lining D to molecular weight using calibrated materials, so you can get out a molecular weight. The problem you face is that typical dextrans are polydisperse so the transition is challenging. I seem to recall, however, that people have fractionated material and then did DLS on fractions. For example, iirc from 40 years ago, Kunitake and research advisor at UCLA did ultracentrifuge, transported the transparent tube to a DLS unit, and did DLS at a series of heights. One might also imagine doing this on electrophoresis (not dextran, clearly) or column output, perhaps with some need to reconcentrate at the output of the fractionation column.
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