Hello everyone,
I am researching three silver sulphide QDs that a collaborating group have synthesised - the cores are all the same size (around 3nm). One is coated in 2MPA, another coated in 2MPA and a targeting peptide, and the last one is conjugated to 2MPA and cetuximab on a PEG linker (probably 1 or 2 antibodies per QD). Hydrodynamic size from DLS suggests that the QD-2MPA is 4.2nm (which makes sense), the QD-2MPA-peptide is 4.8nm (still makes sense) but the QD-2MPA-cetuximab comes back as 5.9nm. On the presumption that an antibody is around 10nm, this must be an underestimate. The first two particles will be spherical, whereas two antibodies on a QD (or even one) will make a non-spherical object, that should be at least 10nm in size. However, I can't find a reference/paper online that explains why DLS might be underestimating the hydrodynamic diameter of a QD-antibody nanoconjugate. I presumed it was shape related, but cannot find published evidence confirming this. Can anyone explain this result, and ideally provide a reference?
Many thanks in advance.
Hello Dr. Peter Labib,
You are correct, with the conjugation you have an increase in the total volume surround your nanocrystal. But, probably you have a non totally spherical coverage for the 3rd system "conjugated to 2MPA and cetuximab on a PEG linker". But before examine de geometry its important check the pH. Do all samples have the same pH? The chemical environment change with pH.
You can try to modify the expected geometry for your nanocrystal in the equipment (from spherical to elongated) and repeat the measurement, this modified the parameters to acquisition of data. Another important parameter is the effective refractive index of your conjugated.
" In comparison, polymer coating employs large molecules to encapsulate the nanocrystals, and the result is a substantial increase in the overall hydrodynamic size of the resulting QDs. However, these ligands are not rigid, and their contributions cannot be treated as simple geometric increases to the radius. (Pons et al., 2006)"
Pons et al., Hydrodynamic Dimensions, Electrophoretic Mobility, and Stability of Hydrophilic Quantum Dots. J. Phys. Chem. B 2006, 110, 20308-20316 (doi: 10.1021/jp065041h)
Hope this helps,
Best regards,
Felipe LN Sousa
Dear Felipe LN Sousa ,
Many thanks for your prompt reply. The pH looks to have been similar for all tests (pH 7.3-7.4). Thank you for suggesting the equipment parameters modification , I will ask my collaborators if this was changed. I'll have a read of the reference too.
Thanks again
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