Читать книгу Magnetic Nanoparticles in Human Health and Medicine - Группа авторов - Страница 50

In this last subsection, some other molecules, not classified in the previous groups, were explored for the clustering of magnetic nanoparticles.

Qiu and coworkers have set a general method for the preparation of nanoparticle clusters in an oil‐in‐water emulsion using cetyltrimethylammonium bromide (CTAB) as an emulsifier (Qiu et al. 2010). To show the general applicability of the method, they prepared clusters of metallic and semiconductor nanocrystals besides magnetic nanoparticles. The obtained clusters were spherical and were composed of densely packed individual nanoparticles, regardless of the type of nanocrystals employed.

Wu et al. started from magneto‐plasmonic nanoparticles (IONPs@Au core‐shell) of 6 nm to prepare nanoclusters, with a diameter of 180 nm, by oil‐in‐water microemulsion method. In detail, hydrophobic nanoparticles obtained by thermal decomposition, in hexane, were mixed with an aqueous solution of sodium dodecyl sulfate. After sonication, the mixture was heated in a water bath at 80 °C for 10 minutes to evaporate the organic solvent. Their superstructure was easily functionalized, by exploiting the gold outer surface of nanoparticles, with thiolated PEG or antibody to ensure a high biocompatibility and a specific target recognition, respectively. The magnetic cluster deserved their superparamagnetic profile, and in addition, the close proximity of the core‐shell particles in the nanocluster led to strong near‐infrared (NIR) plasmon resonances for medical application (Wu et al. 2014).

Smith et al. reported the clustering of 5 nm‐diameter oleic acid‐capped SPIONs in superstructures with very high relaxivity due to control of cluster size coupled with optimization of hydrophilicity at the surface. The authors synthesized different hyperbranched polyglycerol molecules to mimic the properties of glycogen to adsorb water molecules. By emulsification method and subsequent evaporation of the organic phase, regular clusters between 42 and 80 nm were obtained, by tuning the polyglycerol molecular architecture. Interestingly, the r₂ relaxivity passed from 122 mM⁻¹ s⁻¹ of the bare unclustered SPIONs to a maximum value of 719 mM⁻¹ s⁻¹, which was close to their theoretical maximal limit. The described effect was due to two factors: the molecular architecture and to the polyglycerol thickness, and consequently to the hydrophilicity of such coating (Smith et al. 2015).