As T2 MRI are contrast agents, superparamagnetic ironoxide nanoparticles are heavily studied, but I cannot see any studies on Fe nanoparticles. Is it because of the challenge in chemical synthesis or something else?
Mr. Kai, thanks for the reply however I realized my question needs a clarification. Let e put it this way: `Why would a Fe core particle with a biocompatible shell layer such as Au or SiO2 is not used in medical applications?`. In this case, Fe core will be not in direct contact with the environment.
Fe core Fe oxide NPs are potentially highly complex objects. Their magnetic properties are not necessarily favorable for MRI properties. (I actually author a JAP paper (and two further small papers) one one specific such kind of NPs. I don't think these would be very useful at ambient temperature).
Also commissions dealing with authorizing NP materials for clinical applications would have to assess the risk associated with the metal core. I can't tell how potentially harmful these particles are. But as far as I know most kinds of encapsulation of inorganic materials is considered not relieble enough. (This statement probably was fairly accurate some 5 yrs ago. What the situation is today, I don't know).
Mr. Kai, I see that you missed what I asked. I am not asking about iron-ironoxide particles, instead, I am referring to iron core and silica or gold shell particles where metal is encapsulated by a biocompatible layer. My point is also not related to biocompatibity issues because several metal particles with a biocompatible shell are commonly used in bio applications. For MRI t2 signal, volume effect of the magnetic material is utilized which is proportional to the Ms of the material, so, I cannot see why Fe core particles would not be used for MRI. What do you think? Thanks.
The question remains whether the encapsulation is reliable enough so that it would be acceptable to risk assessment agencies. Also, in terms of signal - what will be the figure of merit? Depending on what you plan to do, there will be an upper acceptable particle diameter, may be of order of 500nm or so? Now compare the signal you get with magnetite of that size and the signal you get from Au coated Fe, considering a safety margin for the encapsulation thickness (the encapsulation is not so easy to do (my knowledge on this may be outdated, though)).
Mr. Kai, if encapsulation-wise, there are no issues, would there be a reason why Fe being not used but Fe3O4? I cannot see any reason for Fe not to be used instead of Fe3O4, considering the superior magnetic properties.
I don't know. I have only met people who have sort of given up on looking for different NP materials for clinical applications due to the little hope that these would ever be admitted for diagnostic or therapeutic purposes on humans. i reiterate that this information is already a couple of years old, though.
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