Dear Mohamed G. M. Kordy ,

Plasmonic metallic nanoparticles are indeed non-trivial to measure with DLS. It seems that diffusion is in some way biased leading to oversizing these particles. Next, at sizes from 5-25 nm the presence of a double-layer (which is part of the hydrodynamic diameter measured by DLS) of up-to 5 nm can easily lead to a sizes larger than those measured by TEM or XRD which only gives the hard-sphere diameter. You could try lowering the concentration used in DLS to see if this leads to lower sizes but I would expect DLS and TEM/XRD always to differ.

To answer your question, I know that UV-VIS has been used to size gold nanoparticles, where spectral data were used with Mie scattering theory for spherical particles.

Please check these links for more details:

https://www.researchgate.net/profile/Michael-Nazarkovsky/post/I_got_a_peak_at_422_423_nm_in_UV_spectra_What_is_the_size_of_my_Ag_nanoparticle/attachment/59d62c97c49f478072e9e138/AS%3A273548038344705%401442230343226/download/Au+particles.pdf

https://www.researchgate.net/profile/Rafik-Karaman/post/How_can_I_calculate_the_average_size_for_Au_NPs_fro_UV_Vis_spectroscopy_only_without_TEM/attachment/59d6249479197b8077982e81/AS%3A313834647031809%401451835418167/download/UV-vis+Au.pdf

These papers are readily accessible and should give you an idea how to use your UV-VIS data to obtain a particle size.

Kind regards, Leo

Thank you, Dr Leo Vleugels

I think it's the best answer that I searching for.

Mohamed G. M. Kordy

You say nothing about your metallic nanoparticles, what they are, the route of preparation, or even a simple picture to show that your system is transparent (may be colored e.g. a gold sol) free from turbidity or settling (if so then the system is not nano - < 100 nm)

My translation of 'I think the DLS is not correct' is 'I do not like the (larger) DLS results'. But your question is confused. I read it that you have UV data and want to obtain DLS data from these. You can't convert UV data to DLS data.

Have you actually obtained measurements with DLS? If so you're getting much more information complementary to electron microscopy but you can't compare apples with turnips. What is being measured in both cases is totally different:

• Number distributions versus intensity (proportional to [volume]2) distributions. One expects number distributions to be considerably smaller than intensity (or volume) distributions. If you have a headache and take an aspirin, do you take 4.5 billion particles or 500 mg? There are billions of small particles but they may not make a significant mass (= value/$) for the total system
• Many millions or billions of particles are measured simultaneously in the ensemble DLS measurement. Microscopy may examine only a few (selected) particles
• Incorporation of the protective layer around the metal colloidal particles in the hydrodynamic diameter measured by DLS. With electron microscopy you only measure the electron rich core of the particle ignoring the important surface layer (which governs the stability and the interaction with the environment). The core and the shell are vital properties of the system and useful information (but different) is obtained by comparing the electron microscopy with DLS data
• Agglomerates and aggregates plus contaminating larger material will be seen in the DLS data. If you have small quantities of these larger 'contaminants' then DLS will see them but you may (conveniently) ignore these with electron microscopy
• Further, XRD (line broadening) does not measure particle size, but crystallite size, so again you're making comparisons that are not valid

I have a bunch of questions for you:

• Have you measured your system with DLS? If so did you filter all your liquids to 0.02 μm or better? Please provide some results so we can see the magnitude of the difference
• If yes, then I assume you've verified the performance of the system with the appropriate standard. This removes the instrument from the equation and then you're into an understanding of the techniques issue plus sample preparation
• How many particles did you examine for electron microscopy? To get a standard error of 1% on the mean you will have needed to examined 10000 particles

Dear Dr Alan F Rawle

I have read your comment. There are many questions, you asked and those I want to ask about them. So I suggest contacting you by WhatsApp or Zoom conference because I want to answer them and show you the data and my comments.

My WhatsApp number is 00201062151619

Thank you, sir.

Mohamed G. M. Kordy

Thank you for your reply. I am semi-retired and do not use applications such as WhatsApp or Zoom. I think the questions can be answered on the RG forum and all may benefit from the dialogue. Best regards. Alan

Ok. sir

Hello Mohamed G. M. Kordy

Light scattering is very sensitive to the presence of aggregates, and these might be the reason for your "wrong" result. If you are just off by a few nanometers then the above post by Leo Vleugels should help. For a larger difference you could take a look at https://www.materials-talks.com/blog/2017/01/23/intensity-volume-number-which-size-is-correct/ and https://www.materials-talks.com/blog/2014/07/10/faq-peak-size-or-z-average-size-which-one-to-pick-in-dls/

• UV provides a volume distribution.
• DLS provides an intensity distribution.
• TEM/SEM provide a number distribution

That's great Dr Ulf Nobbmann I checked them and I will conclude them for interpreting the wrong result for the editor, the reason arises this problem.

Thank you for helping me

What are your particles dispersed in for DLS? What particle concentration?

If you don't have some electrolyte present (e.g, 0.1mM KCl) and the particles are moderately/highly charged, you can get electrohydrodynamic retardation which slows diffusion and gives an artificially higher calculated hydrodynamic diameter.

Hi Mohamed G. M. Kordy ,

To answer your question:

UV-Vis spectroscopy and DLS, both measure optical intensities. So a relationship can be drawn. but only to an extent.

UV-Vis and DLS can indeed be combined to get more insight into the particle size distribution. It is common that in DLS, one gets particle sizes significantly higher than TEM or SEM data, this is due to the inherent working principle. The DLS peak shifts to larger sizes as the particle size distribution broadens (shown in the article below and in the attached Figure).

Also, the ligands play a big role in measuring a size much larger than the real size due to variation in the hydrodynamic radius.

In this article, Article Effect of Size Distribution, Skewness and Roughness on the O...

It is shown that the plasmon peak of the UV-Vis spectra of plasmonic nanoparticles can certainly indicate the average size. While the DLS can give the polydispersity (or standard deviation). This is a combined approach of UV-Vis and DLS only applicable to plasmonic nanoparticles.

Hello Mohamed G. M. Kordy

you might like this poster comparing the size of gold nanoparticles, NIST reference material RM8011. It lists the results from AFM, TEM, SEM, DMA, DLS, and SAXS. This should give you a good indication of how different the numbers are for a reference material.

Poster Investigation of Size and Polydispersity of a Nanoparticle R...

Hi Ulf Nobbmann ,

Thank you for the Interesting poster. Indeed a clear comparison of different methods. And even for small sizes, DLS seems to be quite off. But SAXS gives a good estimate from a large population.

Rituraj Borah The DLS results for RM8011 are correct (they are not 'off'). All the mentioned techniques are measuring different things. The SAXS data ignores the protective surface layers and only measures the Au core. The DLS data reflects the total size of the particle including (essential) protective layer. See the NIST certificate for RM8011 (attached).

Hi Alan F Rawle, Thanks for the comment and that's a valid point. Indeed, it was shown in our work that the effect of the polydispersity in the optical spectra becomes increasingly weaker with decreasing particle size. Already for a mean of 20 nm, even a standard deviation of 6 nm did not result in significant band broadening or any band shift. So at 10 nm, the difference between the measurement by light scattering techniques (dependent on the collective optical response) and electron microscopic techniques will be quite small.