SV: [3dem] Re: 3dem Digest, Vol 50, Issue 13

Kimberley Cheng Kimberley.Cheng at
Tue Nov 1 01:29:49 PDT 2011

Thank you everyone for responding to my e-mail! Your answers have been very, very helpful!

All the best,

Från: 3dem-bounces at [3dem-bounces at] för DocDave50 at [DocDave50 at]
Skickat: den 31 oktober 2011 23:33
Till: 3dem at
Ämne: [3dem] Re: 3dem Digest, Vol 50, Issue 13

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 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!
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