[3dem] Re: 3dem Digest, Vol 50, Issue 13
DocDave50 at aol.com
DocDave50 at aol.com
Mon Oct 31 15:33:22 PDT 2011
Hi Kimberley,
This is not unexpected since PCS is providing you with an average size
based on the diffusion coefficient of your vesicles. When you consider that
PCS size determination is based on hard sphere measurements (e.g., latex
bead) and your vesicles are both soft and have a sizeable water of hydration
layer around them, they can "appear" to be larger than what is measured in
the microscope which, assuming all calibrations are correctly done, gives a
correct measure of particle diameter. What I've done with my DLS
measurements of vesicle diameter is to use latex beads with a diameter range similar
to that of my vesicles and modified my parameter set to ensure that they
provide the correct diameter. I appears that this same parameter set best
works for our vesicle work because we have something to correlate the data
to where there is virtually complete size uniformity with the latex beads.
Hope this helps to explain the differences.
David W. Chester, Ph.D.
Department of BioMolecular Science
Imperial College of London
Exhibition Road
South Kensington, London, UK. SW7 2AZ
In a message dated 10/31/2011 10:15:02 A.M. Eastern Daylight Time,
3dem-request at ncmir.ucsd.edu writes:
Dear all,
I recently got the following question "The particle size of our liposome
product determined by cryoEM is about 75 nm, but the particle size
determined by photon correlation spectroscopy (PCS) is about 110 nm. So we were
wondering why the size determined by cryoEM is smaller than by PCS method?".
Does anyone have a good explanation to this?
Many thanks in advance!
/Kimberley
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