Hello Namita,

Remember that mostly suspensions in water of nanoparticles are used for carrying out DLS analysis as the diameter of the particles is called as hydro (water) dynamic diameter. For Fe3O4 (magnetite) particles de-ionized water is used. Although in some cases you can use mixture of other solvents with water and the instrument will calculate automatically the parameters of the solvent mixture to determine the hydrodynamic diameter of the particles. In your case de-ionized water will be a fine disperdent (and not solvent). Once you measure size and zeta potential of your bare and citric capped particles in water at pH 7 then you can prepare buffers to get the standard Zp values profile at different pH to know iso-electric point for your particles.

Good luck.

Hello Sushil, thanks for your answer. I have already used de-ionized water but could not get good results.The results are confusing as with some samples I am getting good Zeta but poor PDI ( polydispersity index ) but for others I am getting both poor, zeta as well as PDI.

On the contrary I got very good particle size with Acetone. I am unable to comprehend the results. Could you pl suggest some thing ?

Hi,

Yes you need a experienced DLS user to the analysis smartly with proper dilution of suspensions with sonication prior to the measurements and import only the good and reasonably reproducible results.

If you are dealing with bare (not stabilized or functionalized ) nanoparticles then your observation is obvious. Magnetites or in general all metal oxide nanoparticles aggregate very fast during the DLS measurements and it makes the sample non homogenous and the PDI is always high (app. 1). The size distribution you obtain is broad or with multiple peaks. PDI value/s indicate stability of the suspension and it should stay below 0.3 . With iron oxides Zp values are reproducible even for bare nanoparticles. You can use citric acid as well known stabilizer for magnetites and then try to determine the size distribution of the citrate stabilized particles. As anyway bare nanoparticles are never used in applications.

In acetone you get good results only because being strongly hydrphillic particles iron oxides tend to aggregate less in non aqueous solvents, but for DLS measurements it is suggested to use water or mixture of water with miscible solvents. Choice of solvent here also depend upon what applications you are targeting.

I hope this helps.

Good luck.

Thanks for your valuable suggestions, it is really helpful.