I prepared some samples of chitosan (CS) nanoparticles cross-linked with sodium tripolyphosphate (TPP) by using the ionotropic gelation method. The particles are used as scaffold for some magnetite nanoparticles (size around 10 nm).
I am trying to narrow the size distribution of CS NPs around 200 nm. TEM imaging showed that the samples were usually highly monodisperse, even when DLS data were promising. I tried to narrow down the size distribution by centrifugating, but I usually obtain an agregated precipitate and a suspension composed by small CS NPs (10-100 nm). This is particularly evident when the CS NPs are loaded with magnetite nanoparticles.
I also tried by filtering through a membrane, but the CS NPs are not stable enough and they are filtered away.
Do you have any suggestions? What's the key in narrowing the size of chitosan nanoparticles? Do you think it's impossible to narrow distribution of chitosan NPs with the TPP cross-linking procedure? Thanks.
You need to remove the magnetite from the system. The long range magnetic forces will overcome any short range charge stabilization you may have put on the system. You may alternatively consider a steric stabilization scenario - e.g. 50 kDa PEG or PEI.
This comment doesn't make sense: ' size distribution around 10 nm'. A distribution provides a range not a single value...
Hi Lorenzo Marsili,
Sometimes the nanoparticles (NPs) formed during cross-linking with TPP can aggregate and can give a false results in DLS/SEM/TEM. I would recommend sonication of the re-suspended NPs at a small pulse and amplitude. Ultrasonic cavitation can help to separate the aggregates to individual NPs.
What was the molecular weight of the chitosan you used? It can be an important parameter. Moreover, you need to synthesize the magnetic nanoparticles utilizing the methods which make a shield around the nanoparticles inhibiting self aggregation.
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