I have prepared a chitosan nanoparticle using ionic gelation method. Then, I measured the particle size using DLS (the measurement around 300 nm with PDI index below 0.2) and looked for nanoparticle structure using SEM. The SEM image didn't agree with the DLS measurement. From SEM, I only see a network of chitosan that formed webbed structure, and fail to see the structure of the nanoparticle. I prepared the powder for SEM using freeze drying directly from suspension of nanoparticles. What analysis must I believe? Is it possible that the SEM image failed because of improper sample preparation? What is the best possible way to prepare chitosan nanoparticle for SEM?
While I am not familiar with chitosan, I would guess that particles may have agglomerated during the drying process, with 'free' nanoparticles available in solution explaining the DLS result.
If your light scattering data shows a good fit with theory, it seems that both analyses are accurate for what you are measuring, but that the preparation method for SEM has caused a change in the sample, resulting in the apparent contradiction.
Perhaps the addition of a surfactant before freeze drying would prevent this.
Thanks.., after searching I would try 3% Tween 80 for stabilizer and 1% Mannitol for Cryoprotectant. Hope it wont aggregate again during lyophilization
We also faced same problem......SEM gives a particular field image but in DLS it will consider entire particles in solution and During sample preparation in SEM, most of the times we lost exact structure.........So DLS results are most appropriate than SEM...........We tried different method for SEm sample prepation, finally we got good results by drying samples directly on the SEM stubs( put 1 to 2 drops) under the 60 watt bulb in a closed chamber or laminar flow.........
it seems SEM has given you the agglomerated image of your nano particles.
it gives you an important information about the stability of nano particles. Either you have kept the nanoparticles at higher temperature for long or the nano particles have unstable because of the absence of stabilizer or capping agents.
Before performing SEM, you must do two steps.
Dilute the sample
and sonicate the diluted samples.
it will break the agglomerated particles. and will give you uniform size.
do the same while performing DLS, PSA, and AFM
Dear All,
Some of our publications that may help you all in synthesis and characterization of chitosan based nanomaterials.
You may see our publication where we did sonication DLS,AAS,TEM SEM and ESD analysis..of chitosan NPs
Article Synthesis of chitosan based nanoparticles and their in vitro...
Article Synthesis and in vitro antifungal efficacy of Cu–chitosan na...
Chapter Synthesis of Chitosan-Based Nanomaterials
Data 2016 Cu-chitosan NP mediated sustainable approach .....maize - JAFC
Book Chitosan Based Nanomaterials in Plant Growth and Protection
vinod sir, thank you so much for sharing your articles
I am also having queries regarding SEM for chitosan based nanoparticles. i got needle like structures in SEM anlysis when i used lyophilized product. whereas when i used solution i got clear spherical shaped particles. It clearly indicates during lyophilization the chitosan becomes flakes, because of that the shape is changing. It is better to take particle size , SEM to the freshly prepared ( diluted) solution.
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