Read this article which is freely accessable:

High throughput synthesis of ethyl pyruvate by employing superparamagnetic iron nanoparticles-bound esterase

May 2018

DOI: 10.1016/j.procbio.2018.05.004

I am interested in this topic! I am performing ab initio calculations in Fe3O4 nanoparticles with diameters from 1 to 3 nm (It has been reported in the literature ultra-small nanoparticles with these diameters). Do you know if there are reports of these core-shell systems with ultra small sizes?

First prepare Fe3O4 NPs with suitable capping ligand which stabilize the MNPs in dispersion and facilitate to anchor the Au or Ar ions from the solution during coating. After washing, disperse MNPs in aqueous media, add Au or Ag precursor salt solution, then dropwise add reducing agent to form metal particles on the surface of MNPs and remove unreacted reagents, and impurities by repeated washing. For silica coating, disperse the MNPs in dry ethanol and add TEOS, AMPS, base (NH4OH), and catalytic amount of water. Run the reaction with magnetic stirring for 24 h at ambient , inert, and dark conditions. You can follow our recent article:

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Thank you Md. Abdur Rahman.