I got smaller particle size in TEM (Transmission Electron Microscope) images as compared to DLS (Differential Light Scattering) measurements of my organic sample in THF/water mixture(60% water).
Several techniques have been used to measure the size of the particles. Each technique has its own advantage and limitation; you might need to read this article for further details Domingos et al., Environ. Sci. Technol. 2009, 43, 7277–7284
In your case, you have to consider the tendency of your particle to agglomerate in an aqueous solution, the surface charge and functional groups of your particles might have an essential role to preserve its monodispersity.
If your particles agglomerate, the values obtained from DLS will be larger than TEM. You might need to measure the particle size with DLS in different aqueous media related to the intended application.
Article Characterizing Manufactured Nanoparticles in the Environment...
As Dr Hardy rightly said, TEM tells you the primary particle size of your particles. But DLS measurements are often done in order to determine the true state of particles in media (especially if they will be applied/studied in media).
DLS data needs to be properly interpreted though by not just taking the "average hydrodynamic size" data by face value. You need to also look size distribution, PDI, and the primary peak % in order to tease out what is going on (e.g. aggregation?).
Best wishes.
TEM gives the size of nanoparticles in dried form while DLS tells the hydrodynamic diameter that includes core plus any molecule attached or adsorbed on surface.. if ur application is for biomedical field then considering DLS is more appropriate
@Hhiraj
A molecular layer corresponds to a few tenths of a nanometer and thus does not significantly change the size of a particle in a solvent
Yes offcourse, DLS will have large size than TEM analysis. Because of principle involves for the analysis in both techniques is different one. DLS shows results including big particle size too as its hydrodynamic diameter therefore has large size than TEM which results due to an scattering of electrons in sample irradiation
Prasad
Please explain why DLS shows big particles or do you mean what mr Hassan already mentioned above?
DLS is an intensity based technique, and this puts higher emphasis on the larger particle sizes. It can be transformed to a number based distribution provided the data quality is sufficient.
TEM is a number based technique, and will thus show stronger emphasis of the smallest components in the size distribution.
http://www.materials-talks.com/blog/2014/01/23/intensity-volume-number-which-size-is-correct/
http://www.materials-talks.com/blog/2014/11/17/tips-tricks-for-nanoparticle-characterization/
Just leave it here.
1. In DLS you measure hydration sphere diameter. The higher charge density (not charge it self!), the bigger deviation. That's why you should use 1-10 mM LiClO4 to suppress the Debay length. In TEM you measure naked particles.
2. Shape. In DLS you measure effective sphere diameter. This, for plates you diameter will be between size of the plate and its thickness. In TEM you may measure both parameters precisely.
3. DLS is a cumulative analysis, it works on hundred thousands of particles in solution, you have very good statistics in the end. TEM is local analysis and, for example, some part of particles tend to aggregate more than another one.
4. in DLS there several modes such as intensity, volume and number, in a broad meaning you have 3 different mean diameters.
I did comparison for various gold nanoparticles between DLS, TEM and UV-Vis size methods to determine this distribution. The results can be found in the thesis (link is attached). The diameters are comparable only for middle range of nanoparticle diameters.
https://infoscience.epfl.ch/record/224442
I guess the answer in this article:
Particle Size Determination Using TEM: A Discussion of Image Acquisition and Analysis for the Novice Microscopist
Langmuir 2008, 24, 11350-11360
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