Dear Sir. Concerning your issue about how to synthesis silica coated magnetite nanoparticles . Magnetic Fe3O4 nanoparticles were prepared by coprecipitation and then coated with silica. These Fe3O4/SiO2nanoparticles consisted of a 10–15 nm magnetic core and a silica shell of 2–5 nm thickness. The superparamagnetic property of the Fe3O4/SiO2 particles with the magnetization of 42.5 emu/g was confirmed by vibrating sample magnetometer (VSM). We further optimized buffers with these Fe3O4/SiO2 nanoparticles to isolate genomic DNA of hepatitis virus type B (HBV) and of Epstein-Barr virus (EBV) for detection of the viruses based on polymerase chain reaction (PCR) amplification of a 434 bp fragment of gene specific for HBV and 250 bp fragment of nuclear antigen encoding gene specific for EBV. The purification efficiency of DNA of both HBV and EBV using obtained Fe3O4/SiO2 nanoparticles was superior to that obtained with commercialized Fe3O4/SiO2 microparticles, as indicated by (i) brighter PCR-amplified bands for both HBV and EBV and (ii) higher sensitivity in PCR-based detection of EBV load (copies/mL). The time required for DNA isolation using Fe3O4/SiO2 nanoparticles was significantly reduced as the particles were attracted to magnets more quickly (15–20 s) than the commercialized microparticles (2-3 min). I think the following below links may help you in your analysis:

https://www.hindawi.com/journals/jnm/2013/603940/

https://pubs.acs.org/doi/abs/10.1021/la0008636

https://www.sciencedirect.com/science/article/pii/S0921883111001488

http://www.ingentaconnect.com/contentone/asp/jnn/2018/00000018/00000002/art00111

Thanks

This could be useful

I also suggest the works of Wagner et al.. He works with well defined core shell particles.

Joachim Wagner

In this case there are two types of processes Soft template and hard template technique. Silica is a slimy type of material so that sometimes if you synthesize little bigger size magnetite nanoparticle then also it get encapsulated in silica using some appropriate surfactants as a driving force in it.