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

[DocDave50 at aol.com]

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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