You can also use zetasizer for size measurements as an additioanl tool to that of TEM. Zetasizer measures particle size as hydrodynamic diameter which is usually based on differential light scattering measurements. If your zetasizer measurements agree with TEM results, it is more accurate and precise measurements for size analysis. Then size which you will measure from zetasizer that will be your (as in most cases in literature) hydrodynamic diameter in your research report. Further i will suggest you to fo malvern zetasizer website. Thoroghly study it, you will get a lot of information. Hope this will help you.

http://www.malvern.com/en/products/product-range/zetasizer-range/zetasizer-nano-range/zetasizer-nano-zs/

Hello,

The answer is depends on the goal. Usually for description of non-spherical particles this simple form is used: "there are rod-shaped and pyramidal particles with characteristic size 30-50 nm" with few TEM pictures. It's enough for a lot of cases.

It is possible to use the simple spherical approximation with average R for estimation of surface area (obviously, if the particles are not plates or long rods): the geometrical error will be not more than effect of the inhomogeneity of shape and size of particles. 

Good luck! 

Thanks, Muhammad Imran Khan,

I will do this. Actually I am to do this analysis very soon. I waited for the in vivo results...You are wright, I have to report the zeta potential too.

I agree with Denis Korneev too. I know that I have to approximate the volume to a sphere. In this case I receive much "smaler" average diameter than the reported in other articles. Anyway, your suggestion is correct.

Dear Dr. Maria Traykova,

Most of authors when they report particles size from SEM or TEM, they assume that particles have spherical or almost spherical shape (so it becomes easier to report the diameter(d=2 r) and calculate the surface area). If your particles do not have spherical shape (ex: pyramidal, triangle), then it would be better to report the surface diameter (more easier and you need only to measure two variables h and b, if you want to report the volume you need to measure the 3 variables (l,h,w), remember that TEM image is 2D, so you need 2 or 3 images of the same sample from different angle to be able to measure the 3 variables correctly). The zetasizer will be helpful to use only for spherical particles, you can use the zetasizer to measure the zeta-potential of your Ag NP, but I do not think it will be good idea to use it to measure the pyramidal particles average size.  There is a software that can help you measure the average surface area of your pyramidal particle and it is free (ImageJ).

Dear Maria,

did you already try metal shadowing of particles attached to the support film? You could obtain information such as shadow length (for hight if you carefully control the angle of shadowing and the amount of metal for shadowing), and you could detect possibly existing  preferential orientations of the particles attached to the support film distributed over the field of view. This would allow you to get additional information on any preferred particle shape(s). By the way: you can, most probably, mount the particles on the support film by a diffusion technique (floating the support film on top of the particle suspension, wait until sufficient numbers of particles are attached) and then lift the support film off from the suspension from underneath by a copper grid). - Note that such a diffusion technique will, within the first few seconds, collect the smallest particles,; later, bigger ones will follow. -

 Good luck!

Frank Mayer.

 Dear Maria,

You can use Dynamic light scattering characterization of  size distribution and percentage of nanoparticles. please see the supporting information in our work "Dual-Cargo Selectively Controlled Release Based on a pH-Responsive Mesoporous Silica System".

Good luck!

Wanyuan Gui