Surface functionalization for tailoring the aggregation and magnetic behaviour of silica-coated iron oxide nanostructures

Abstract

We report here a detailed structural and magnetic study of different silica nanocapsules containing uniform and highly crystalline maghemite nanoparticles. The magnetic phase consists of 5 nm triethylene glycol (TREG)- or dimercaptosuccinic acid (DMSA)-coated maghemite particles. TREG-coated nanoparticles were synthesized by thermal decomposition. In a second step, TREG ligands were exchanged by DMSA. After the ligand exchange, the ζ potential of the particles changed from -10 to -40 mV, whereas the hydrodynamic size remained constant at around 15 nm. Particles coated by TREG and DMSA were encapsulated in silica following a sol-gel procedure. The encapsulation of TREG-coated nanoparticles led to large magnetic aggregates, which were embedded in coalesced silica structures. However, DMSA-coated nanoparticles led to small magnetic clusters inserted in silica spheres of around 100 nm. The final nanostructures can be described as the result of several competing factors at play. Magnetic measurements indicate that in the TREG-coated nanoparticles the interparticle magnetic interaction scenario has not dramatically changed after the silica encapsulation, whereas in the DMSA-coated nanoparticles, the magnetic interactions were screened due to the function of the silica template. Moreover, the analysis of the AC susceptibility suggests that our systems essentially behave as cluster spin glass systems.

Iron oxide nanoparticles fabricated by electric explosion of wire: focus on magnetic nanofluids

“…3,5 Nowadays, MNPs of the iron oxides have become important components in biosensing, magnetic separation, advanced medical screening and therapies, including bio-assays, magnetic resonance imaging (MRI), magnetically guided drug delivery, and hyperthermia, etc. [5][6][7][8][9] Thanks to a variety of excellent properties, magnetite MNPs were also used in many non-biological applications such a Author to whom correspondence should be addressed. Electronic mail: galina@we.lc.ehu.es.…”

Fe3O4/SiO2 Core/Shell Nanocubes: Novel Coating Approach with Tunable Silica Thickness and Enhancement in Stability and Biocompatibility

“…The saturation magnetization value, extracted from the corresponding Reverse Microemulsion method > 16 h [8] General method > 16 h [9] Reverse Microemulsion method 48 h [7] Sol-gel method 6-48 h [1] Microemulsion method 24 h [6] Microemulsion method 20 h [5] Modified Sol-gel method (Our method) 4 h - hysteresis loop, for the uncoated magnetite sample at 300 K is 80 emu/g, and it decreased for the coated samples as expected to be 50.7, 46.1, 43.8, and 42 emu/g, respectively with increasing the thickness of silica shell. The decrement in magnetization value after coating with silica in all the samples may be attributed to the incorporation of nonmagnetic silica shell around the core magnetite nanocubes.…”

“…Even though there are many kinds of materials available for coating of the magnetic nanoparticles, like metal oxide, noble metals and polymer material, the silica is still considered to be the best candidate for surface functionalization because it is highly stable against degradation. Furthermore, silica act to improve the biocompatibility, hydrophilicity as well as the surface functionality due to the availability of abundant silanol groups (-SiOH) on the surface [1], which makes it as a promising materials for different kinds of bio-applications.…”

Pros and Cons on Magnetic Nanoparticles Use in Biomedicine and Biotechnologies Applications

“…• Cover of magnetic nanoparticles with organic compounds, including surfactants [84][85][86][87] and polymers [88][89][90][91]; • Coating of magnetic nanoparticles with inorganic compounds, including silica gel [92][93][94], carbon [95,96], and precious metals (Au [97,98], Ag [99]). …”

“…Many studies described the role of functional groups, which control reactivity and colloidal properties of magnetic suspension, as well as the influence of alkaline reagents, concentration of coated nanoparticles, water/alcohol ratio, or concentration of TEOS on final morphological aspect of these nanostructures [92,93,112,113].…”