I have attached two papers describing mesoporous silica encapsulated nanoparticles as MRI contrast agent. In MRI, we see the realaxation of body water protons. The more the relaxation is the better the contrast becomes. MRI contrast agents help in improving the contrast by increasing the water proton relaxation. Though Mn2+ based nanoparticles can be promising MRI CAs, considering adverse effects of manganese deposition inside the body, they were coated with silica to make them biocompatible. However, it led to the shielding of the core nanoparticles from the surrounding water molecules leading to low value of water proton relaxation. Therefore, the idea of encapsulating the nanoparticles by mesoporous silica evolved.
While using this mesoporous silica coated MRI CA for in vitro or in vivo purposes, one has to make them water soluble. In that case, is not it possible that the core nanoparticles can come out through the pores after getting dissolved in water? Even inside the body, can't the water molecules getting access to the core bring out the nanoparticles out of the core in the form of solution?
Article Mesoporous Silica-Coated Hollow Manganese Oxide Nanoparticle...
Article Structure-property relationships in manganese oxide–mesoporo...
Silica coated iron oxide nanoparticles will eventually dissolve into the solution with time. During your preparation steps what pH solutions do you use? Please see my publication where we have monitored the rate of SPION dissolution at different pHs (7.4 to 4.5) with time.
http://pubs.rsc.org/en/Content/ArticleLanding/2012/CC/c2cc34420c#!divAbstract
I would not say that the MnO nanoparticles "come out through the pores". Instead, what is certainly possible is for the MnO to dissolve one ion at a time, resulting in the nanoparticles leaching from the pores. Subtle difference, but possibly important given the exact application (for example - desired residence time in vivo).
The porous silica and PEGylated surface could slow down the dissolution of the core particles by blocking the physisorption or chemisorption of biomolecules from the body (proteins, peptides, immune cells, etc) that may rapidly degrade bare MnO.
I believe, yes, it should get released from the shell eventually, but the release will be slow and not burst.
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