Synthesis and characterization of functionalized silica-coated Fe₃O₄superparamagnetic nanocrystals for biological applications

Abstract

Superparamagnetic Fe3O4 nanocrystals were prepared by a chemical coprecipitation method with a thin thickness-adjustable silica layer coated on the surface by hydrolysis of tetraethyl orthosilicate. The silica-coated Fe3O4 nanocrystals were well dispersed and consisted of a 6–7 nm diameter magnetic core and a silica shell about 2 nm thick, according to transmission electron microscopy observations. Fourier transform infrared spectra revealed that amino (–NH2) groups were successfully covalently bonded to the silica-coated Fe3O4 and then carboxyl (–COOH) groups were functionalized to the surface through the reaction of –NH2 and glutaric anhydride. The synthesized nanocrystals have a cubic spinel structure as characterized by x-ray diffraction, electron diffraction and high-resolution transmission electron microscopy. Their magnetic properties were carefully investigated by a SQUID magnetometer. The results showed that the nanocrystals were superparamagnetic and the blocking temperature TB shifted from 131 K down to 92 K after they were coated with a thin nonmagnetic layer, since this layer can effectively suppress the magnetic dipolar interaction between particles; the chemically inert silica layer can limit the outside environment effect on the Fe3O4 cores quite well due to the excellent magnetic reproducibility of the coated nanocrystals after ageing for 7 months at room temperature. In addition, the dependence of their high-field specific magnetization on temperature has a T2 relationship. These functionalized silica-coated Fe3O4 superparamagnetic nanocrystals have great potential in biomagnetic applications.

The cell labeling efficacy, cytotoxicity and relaxivity of copper-activated MRI/PET imaging contrast agents

“…The lowering of T B was observed in the literature when the nanocrystals are chemically coated with a thin layer of nonmagnetic material. The T B of the nanoparticles was suppressed to a lower temperature compared to that of the approximately similar sized uncoated nanoparticles [63]. The (MnO)7-L samples showed the antiferromagnetic behavior at 2 K [64] and [36].…”

Superparamagnetic Iron Oxide Nanoparticle Probes for Molecular Imaging

“…114 The degree of silica-coating can be controlled, 11 resulting in coverage thickness between 2 and 100 nm. 85 The hydroxyl surface groups can be modified to display functional amines and carboxyls, relevant for further bioconjugation 56 and the silica itself can be dyedoped. 85,114 As mentioned earlier, SPIO can also be formed directly in the presence of a coating polymer, usually dextran, 93,156 although a variety of coating systems are available (Table 2).…”

Preparation of silica coated cobalt ferrite magnetic nanoparticles for the purification of histidine-tagged proteins

“…Furthermore, the hydrophilic surfaces of silica-coated magnetic nanoparticles can be modified with the functional groups. In addition, magnetic nanoparticles should be coated with silica layer before they were used in a biological application because silica was a nontoxic material (He, Wang, Li, Miao, Wu, & Zou, 2005). …”

“…After silica shell was coated on the cobalt ferrite nanoparticle, the surfaces of these nanoparticles were modified with amine groups by APTES (He, Wang, Li, Miao, Wu, & Zou, 2005). At this process 12 ml DMF and 8 ml toluene were vortexed in a 50 ml tube and this solution was put in a 50 ml beaker.…”