Does it require dispersion of ZnO in some solvent or a colloidal medium? because it is told that ZnO starts precipitating during the measurements of Dynamic Light Scattering
Hi. We are actually working with ZnO NPs. They effectively precipitate and aggregate depending on several experimental conditions including concentration, ionic strenght, pH. Be careful using buffers as ZnO becomes soluble at high and low pH. The range of pH within which it does not dissolve significantly is rather narrow. The way to prepare your solution should take into account the objective of the measurements. Some molecules from the buffer can be involved in the NPs coating and increase their hydrodynamic size. For the stimation of the average size and size distribution of particles of a ZnO NPs dispersion at specific pH and concentration, it could be necessary to do it after sedimentation of the precipitate if any. The impact of the dilution of the dispersion on the size and distribution of size could also be pertinent. If you are making your dispersions from powders, the protocole should be carefully controlled to ensure reproducibility.
Hi Prashanth, I haven't worked with ZnO nanoparticles but I overcame this issue with silicon oxide particles by using a buffered solvent (HEPES) and by measuring very small concentrations (as close to the limit of detection as possible). Also, instead of using intensity PSD or volume PSD based read-outs, try looking for a number PSD result. This will exclude the intensity derived from larger clumps and will generally return average sizes comparable to electron-microscope measurments of nanoparticles. Best of luck!
Hi. We are actually working with ZnO NPs. They effectively precipitate and aggregate depending on several experimental conditions including concentration, ionic strenght, pH. Be careful using buffers as ZnO becomes soluble at high and low pH. The range of pH within which it does not dissolve significantly is rather narrow. The way to prepare your solution should take into account the objective of the measurements. Some molecules from the buffer can be involved in the NPs coating and increase their hydrodynamic size. For the stimation of the average size and size distribution of particles of a ZnO NPs dispersion at specific pH and concentration, it could be necessary to do it after sedimentation of the precipitate if any. The impact of the dilution of the dispersion on the size and distribution of size could also be pertinent. If you are making your dispersions from powders, the protocole should be carefully controlled to ensure reproducibility.
Hi Prashanth,
ZnO nanoparticles are not very soluble in water. SO, the best thing for you to do is to contact the manufacturer of your DLS instrument and get their experience in working with water insoluble or slightly soluble materials. More than anyone else, they will have the best solution and criteria regarding the capabilities of their instrument. They may even want to test the ZnO at thier won facility.
Hi Prashanth,
Louise is absolutely correct. I've worked with TiO2 NPs and the conditions are very similar. Very small nanoparticles have a greater average (ensemble) velocity and tend to incur a greater number of collisions; therefore, larger particles generally have a lower rate of aggregation. Now in regards to the pH, what is very important in dispersing nanoparticles is that you prepare a solution with a pH that is not near the isoelectric point of the material. This parameter can change with size so you need to look up specifics if you want to be accurate. The reason that this is important is simply due to the interaction dynamics on the molecular scale. If the particles are without surface charge, attractive forces dominate and aggregation occurs. Finally, what I found most useful is to prepare a solution with the appropriate pH prior to adding any particles. This will stall the initial aggregation kinetics which seem to be the most crucial. Of course, finding the appropriate pH for your system will take a bit of research, but once you've isolated the appropriate conditions I'm sure you will see a great difference. I've attached a paper that describes these criteria for TiO2. Hopefully this will help you with ZnO. Best of luck!
Hi, I don’t work with ZnO powder in our lab but i share my experience with you (it maybe helpful). We prepare a transparent solution containing ZnO nanoparticle from a Zn precursor by sol gel method. Then we can easily measure its size by DLS.
Hello
A nice method could be found in the following protocol.
http://www.nanotechia.org/sites/default/files/files/PROSPECT_Dispersion_Protocol.pdf
and the other
https://www.researchgate.net/profile/S_Milne/publication/267225845_Measuring_the_dispersion_of_ZnO_nanoparticles_in_solutions_for_cell_viability_assays/links/54f5d5d70cf27d8ed71ccb00/Measuring-the-dispersion-of-ZnO-nanoparticles-in-solutions-for-cell-viability-assays.pdf?origin=publication_list
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