This is a good question. I too would like to hear some insights in the matter. One thing I do know, in general, is the the hydrodynamic size is generally not in agreement with the true TEM-measured size.

Well, in my opinion, both are "true" size. They are just two different things, with TEM you measure the core size and with DLS you have into account the surfactant and the interaction with solvent molecules. Of course TEM is important but for me, working on nanoparticles for bioimaging, is much more important the hydrodynamic size. A nanoparticle with 5 nm size and homogeneous in TEM that once in water is 1000 nm is worthless.

Good question. I'll try and answer your question part by part from what I understand. Firstly, as we already know that by DLS we get the hydrodynamic radius of the particle whereas by TEM we get an estimation of the projected area diameter. So as far as DLS is concerned, the theory states that when a dispersed particle moves through a liquid medium, a thin electric dipole layer of the solvent adheres to its surface. This layer influences the movement of the particle in the medium. Thus the hydrodynamic diameter gives us information of the inorganic core along with any coating material and the solvent layer attached to the particle as it moves under the influence of brownian motion. While estimating size by TEM, this hydration layer is not present hence, we get information only about the inorganic core. The projected area diameter estimated by TEM is theoretically defined as the area of a sphere having the same area as the projected area of the particle resting in a stable positon. Sometimes due to poor contrast in TEM the size measurement of the coating layer if present could be underestimated or missed. Hence, the hydrodynamic diameter is always greater than the size estimated by TEM.

Talking about the importance of the hydrodynamic diameter, many studies suggest that it is an important paramater for understanding and optimizing the nanoparticles' performance in biological assays as well as understanding the in vitro migration of the particles.

As Adam states, there is frequently disparity between electron microscopic measurements and hydrodynamic (DLS, zetasizer) measurements. This is particularly true for 'hard' particles (e.g. metallic, such as iron oxide particles).

From my PhD and recent paper, with references:

http://www.futuremedicine.com/doi/abs/10.2217/nnm.12.145?url_ver=Z39.88-2003&rfr_id=ori:rid:crossref.org&rfr_dat=cr_pub%3dpubmed

"The hydrodynamic diameter of the MPs was found to be in the range 843–961 nm

(Table 1), that is, larger than that measured by scanning electron microscopy analysis (~360 nm). The former values were determined by dynamic light scattering [DLS], a technique that measures the hydrodynamic diameter of the particle including the solvation layers. It should be noted that measurements by dynamic light scattering are more accurate for soft materials, such as proteins, with the size of more dense materials being commonly overestimated [33, 280, 337]; our observations are consistent with the literature relating to MPs, where different methods of size-determination can produce conflicting data. [34, 280]."

[33] De Palma R, Peeters S, Van Bael MJ et al. Silane ligand exchange to make hydrophobic superparamagnetic nanoparticles waterdispersible. Chem. Mater. 19, 1821–1831 (2007).

[34] Olariu CI, Yiu HHP, Bouffier L et al. Multifunctional Fe3O4-PEI-RITC nanoparticles for targeted bi-modal imaging of pancreatic cancer. J. Mater. Chem. 21, 12650–12659 (2011).

[280] Dhawan, A. & Sharma, V. Toxicity assessment of nanomaterials: methods and challenges. Anal. Bioanal. Chem. 398, 589–605 (2010).

[337] De Palma, R. et al. Silane ligand exchange to make hydrophobic superparamagnetic nanoparticles water-dispersible. Chem. Mater. 19, 1821–1831 (2007).

I appreciate your contributions to this forum and they are good ingredients to us young scientist working in nanotechnology. In my current research in lipid nanoparticles I opted to use both Cryo-TEM and DLS, so that I can get well defined sizes of particulates, although I was at junction on reporting the case.

Thanks

in line with the various contributions can i say that for stable nanoparticles such gold NP, TEM AND DLS size should be in agreement while unstable NP that requires surfactant such as iron oxide NP TEM and DLS should not be in agreement.

DLS calculations are based on Stokes–Einstein equation, this is the source of all drawbacks. TEM is more accurate, but tells You nothink about Your particle behaviour in liquids.

Depending on the Nano particle size range, XRD (both SAXS & WAXS), will yield the diffracting domain size which is a better estimate of the true "hydrodynamic size of nanoparticles" in the sample composite. These XRD measurements may be REAL TIME & NON-DESTRUCTIVE in nature. Measurements are in situ. Use of "calibration samples" (of known size distribution) greatly enhances the certitude of the measurements using XRD.

TEM will yield the size range in a highly localized area of the sample. Sample preparation is tedious and destructive. Data must be interpreted with "care".

@RAvi

XRD gives the domain size

Harry! I stand corrected. I need to better familiarize myself with the definition of "hydrodynamic size". I notice a huge controversy in the definition of particle size & grain size already. Adding "hydrodynamic size" to the mix makes it even more interesting :-) Does it mean with the pores or without? I'll read up now. Nano particles themseves may be polycrystalline as well. Thanks!

I'm in agreement that the XRD gives diffracting domain size. It may be possible to determine core size with XRD as well. I know mesoporosity is quantifiable with XRD (SAXS).

So a single crystal XRD rocking curve FWHM may then be used to compute the average dislocation "cell size". What if the profile is distorted from the expected shape of the instrumental profile? How do you interpret the distortion in the reciprocal space in terms of Nano structure (real space)? I'm looking for literature if available in PDF format. Thanks! [email protected]

I would like to know what information we get from Atomic force microscope. Do we get data same as DLS or like TEM for NP+Capping Layer where one is organic and another is inorganic.

Fernando Herranz @ I agree with you sir.

To Ruchira Sarbajna  Question(I would like to know what information we get from Atomic force microscope. Do we get data same as DLS or like TEM for NP+Capping Layer where one is organic and another is inorganic.) 

Both AFM and TEM will give the same partlcles size. DLS gives hydrodynamic size

Dear friends

We know many methods for nanoparticles size measurement, but bear in mind that nano is already a bit like quantum mechanics. If nanoparticle is made of liquid, last layer is not really well attached to the bulk, it is a sort of virtual or cloud like. In the case of “very solid” particles (Ag) in gas or liquid environment we always have adsorbed molecules. Only solid nanoparticles in high vacuum are pure, at list I believe so…

Is this adsorption layer meaningful? In water a single layer of adsorbed surfactant (simple soap) increases diameter of about 3-4nm, and usually we have multiple layer of surfactant and water molecules, which are more and more virtual with increasing distance from the surface. When nanoparticle adsorb water also inside, the diameter change a lot. For example we make nanoparticles for cancer treatment, they are 12nm dry and about 100nm in water. High water content is sometimes helpful in drug delivery, decreases small blood plasma protein adsorption. Such nanoparticle in water is rather a cloud…

There is also another problem, measuring devices… DLS and NTA (nanoparticle tracking analysis) base on the same, Einstein-Stokes equation and should measure the same parameter – diffusion and recalculate it to get hydrodynamic diameter (responsible for diffusion in liquids). They should give the same results but it is not true… This was theory, in practice devices employ very complex deconvolution algorithms, they do a lot of magic and demand a lot of data, and finally we get what we get. Simple update of the software of well-known devices can change measured diameter for 2-10%, and the change depends on the material which build nanoparticles…

SEM and TEM are good for solid metallic NP. In the case of airborne nanoparticles DMA (differential mobility analysis) is also very accurate and relevant, but again, it measures mobility equivalent diameter, not just diameter. You can always make Your nanoparticles airborne by EHDA (electrospray).

Ergo, if You work with nanoparticles:

1. Don’t trust Your measuring device.

2. There are no absolute measurement methods, they are all comparative, especially in nano world.

3. Try to use standards for calibration, best are made by the Principal Engineer (or nature), like proteins, very well defined weight, at list one parameter. (human serum albumin 66.5 kDa)

Thanks for the feedback.  Dear Arunas, I did not really understand your reply. I am clear on TEM and DLS. But does AFM give the information of the localized nanoparticle as a whole? that is the diameter of both the inorganic and organic (capping) material? Then can I say that size obtained by AFM will be similar to that obtained by DLS and always greater than that obtained by TEM?

DLS measures the hydrodynamic size, in other words the size with any solvent molecules attached to the outside of the nanoparticle. The direct observation are the intensity fluctuations due to the diffusion of the particles, and this diffusion coefficient is then interpreted as a hydrodynamic size using the Stokes Einstein equation. (The diffusion coefficient is compared to that of a hypothetical sphere moving with the same diffusion coefficient).

An additional key difference between the techniques is that TEM is a number-based observation whereas DLS is an intensity-based observation. The direct intensity size distribution may therefore inherently be weighted to larger sizes than the number distribution, due the fact that the scattering intensity is proportional to size^6. Under ideal conditions the number distribution transformation of the DLS result should be very close to the TEM size. For polydisperse samples this will be more difficult to observe.

http://www.materials-talks.com/blog/2014/01/23/intensity-volume-number-which-size-is-correct/

http://www.materials-talks.com/blog/2014/07/10/faq-peak-size-or-z-average-size-which-one-to-pick-in-dls/

Please read our newest published paper on this topic:

http://pubs.acs.org/doi/pdf/10.1021/acsami.6b06903

Fernando Herranz

Sir, Can you give me any reference for the comment you have posted. 

I.e actual data where there is a contrast is showed between these 2 values

As an example of a very large difference between hydrodynamic and geometric sizes possible for biological nanoparticles, you may want to look at our paper focused on sizing exomsoes:

https://www.researchgate.net/publication/274254357_Size_and_shape_characterization_of_hydrated_and_desiccated_exosomes

Article Size and shape characterization of hydrated and desiccated exosomes

Well, I think that basically it is the technique that we are adopting to measure the size at nanoscale that determines the particle size. Further hydrodynamic diameter of a nanoparticle depends on the what type of dispersing media (atmosphere) it is sorrounded by...But always it would be greater than that given by TEM.

How much larger?

A single solution layer is a few tenths of a nanometer

As an example just take a look at the certificates provided by NIST for the RM801x gold colloid materials with nominal size 10 (especially), 30, and 60 nm.

https://pubmed.ncbi.nlm.nih.gov/21116952/

https://www.researchgate.net/post/Hydrodynamics-size-of-nanoparticles