I synthesized Gold-coated iron oxide nanoparticle using citrate reduction method. I measured the DLS before coating (6 nm) and after coating (7nm). I also measured TEM. Is my TEM images (attached) right for gold coated iron oxide nanoparticles? If so, why is the size of the nanoparticles differs from DLS (I got 3 nm core, 1.5 thickness shell)? Thanks!
Hi Christian,
DLS and TEM are measuring different things, so it should not be a surprise that the size measured is different. TEM measures the physical size of dry materials whereas DLS measures the hydrodynamic size in dispersion. It is therefore possible for the size of the particle to be fractionally different when dry and in dispersion, but additionally DLS is measuring size based on how the material diffuses, and typically DLS analysis assumes spherical particles.
Lastly, DLS is an ensemble technique and reports the average size from a large number of particles, whereas TEM is a number based technique where the number of particles measured is typically far fewer than in DLS.
This has come up a number of times before on ResearchGate and there have been some indepth discussions on the pros and cons of each method.
https://www.researchgate.net/post/Why_does_the_particle_size_differ_in_TEM_and_DLS_measurements
https://www.researchgate.net/post/Why_was_there_size_difference_measured_by_TEM_and_DLS
https://www.researchgate.net/post/Why_the_pattern_of_particles_size_different_between_DLS_and_TEM_analysis
DLS is an ensemble technique and reports the average size from a large number of particles, whereas TEM is a number based technique where the number of particles measured is typically far fewer than in DLS.
From your Fig. it is not clear how you have determined the size of the core3 nm and shell 1.5 nm. Gold in a picture should be darker than iron oxide. You need to investigate the dispersion method SAXS. You compare the size of the three methods and then answer the question for yourself. You will be useful to see my discussion with experts Malvern.
https://www.researchgate.net/post/Highly_reliably_data_DLS
https://www.researchgate.net/post/While_measuring_particle_size_with_DLS_it_never_says_good_sample_quality_What_may_be_the_probable_reason_for_this#view=58a1e158404854d9bf02e3f5
Best regards.
To Alexander and Zaid : Thank you a lot!
To Yuri Migorod : Thank you, I analyzed the figure with ImageJ software, assuming they are spherical, and compared the results with TEM images of iron oxide only. Why should the gold be darker than iron oxide? I read several publication and it's always said that iron oxide should be darker.
Dear Christian,
You do not write the structure of the oxide: magnetite, goethite, hematite. They all have residual hydroxyl groups. Oxides are less dense, they must be loose, if you do not calcined. It turns out that the background of translucent particles is gold? A lot of aggregates. How did you process the aggregates of particles?
Уou can not reply. The answers are not for me, but for you.
Best regards.
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