Instrumentation for Dynamic Light Scattering

Andrew, Tel. +39-6-91093434 WALLACE at IRBM.IT
Mon Mar 28 12:44:41 EST 1994

Dear Michael,
There is a US company called Wyatt Instruments (sorry, don't know their
address or phone #) which makes a laser-based device which can measure the
dynamic radius of macromolecules in solution. Their dealer here in Italy
lent a machine to us for a few days last year and we tried it out on a
number of small peptides of <60 residues. Unfortunately the instrument
we saw used a frequency of (red) laser light which made it rather insensitive to
molecules in this molecular weight range, though we had indications that it
could detect something only slightly larger, say from 8 kDa on up.
The higher the MW, the more sensitive the response. Our conclusions were two:

1) The device was not sensitive enough in the MW range we were interested in
   (<8 kDa).  We needed mg quantities to see even a hint of a signal, which 
   rendered it impractical for our purposes. The method is non-destructive,
   though, so you can easily re-use any sample you are working with if 

2) Despite obtaining some interesting-looking data, we had no idea how to
   interpret it and, it seemed, neither did Wyatt's rep. They appeared to be
   aiming the instrument at the industrial polymer chemistry market and 
   apparently didn't have much experience on handling protein data.

In the end we didn't buy the instrument although the demo worked well as far
as it went. I'd certainly consider buying one if I was routinely working with
larger proteins. One other thing - if you are interested in measuring solution
MW by this method, you need to provide the device with an instrument signal
which is proportional to the mass of the sample, say from a refractive index
detector, for example. This is because the light scattering signal does not
give an absolute measure of the MW, it is only proportionally related to it
(assuming that the molecule of interest obeys a given set of properties). 

I'm not sure if this was the kind of information you were looking for, but I
hope it helps.

		Andrew <wallace at>

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