Magnetic nanoparticles: synthesis, functionalization, and applications in bioimaging and magnetic energy storage

Abstract

This tutorial review summarizes the recent advances in the chemical synthesis and potential applications of monodisperse magnetic nanoparticles. After a brief introduction to nanomagnetism, the review focuses on recent developments in solution phase syntheses of monodisperse MFe(2)O(4), Co, Fe, CoFe, FePt and SmCo(5) nanoparticles. The review further outlines the surface, structural, and magnetic properties of these nanoparticles for biomedicine and magnetic energy storage applications.

Fig. 1

Schematic illustration of (a) a typical hysteresis loop of an array of single domain ferromagnetic nanoparticles and (b) a typical curve for a superparamagnetic material.

Fig. 2

(a) Schematic illustration of the LaMer model: separate nucleation and growth for the synthesis of monodisperse nanoparticles; (b) a typical “hot-injection” set-up to achieve the burst nucleation in (a). Reprinted from ref. 13 with permission from Annual Reviews.

Fig. 3

TEM images of (a) the as-synthesized 8 nm/2.5 nm Fe/Fe₃O₄ NPs (inset: HRTEM) and (b) the 5 nm/5 nm Fe/Fe₃O₄ NPs prepared by controlled oxidation of Fe NPs. Reproduced from ref. 19 with permission from the American Chemical Society.

Fig. 4

Schematic illustration of NP surface functionalization via (a) surfactant addition and (b) surfactant exchange.

Fig. 5

(a) Schematic representation of the amphiphilic micelle coating of the CoFe NPs; (b) high-resolution TEM image of a single CoFe NP. Adapted from ref. 31 with permission from Nature Publishing Group.

Fig. 6

Magnetic Fe₃O₄ NPs with bifunctional ligands. (a) Surface coating of iron oxide with a dopamine-termination. (b) Water-soluble Fe/Fe₃O₄ core–shell nanoparticles coated with bifunctional PEG ligands.

Fig. 7

Size-dependent MR contrast effect of MnFe₂O₄ and Fe₃O₄ NPs. (a) TEM images of MnFe₂O₄ NPs (scale bar, 50 nm), (b) T₂-weighted MR images, (c) color maps of 6, 9 and 12 nm MnFe₂O₄ NPs, and (d) a plot of NP size versus R₂ relaxivity. Reproduced from ref. 37 with permission from Nature Publishing Group.

Fig. 8

Color maps of T₂-weighted MR images of a mouse implanted with the cancer cell line NIH3T6.7 at different time points after injection of MnFe₂O₄–Herceptin (a–c) and Fe₃O₄–Herceptin (d–f) conjugates. Adapted from ref. 37 with permission from Nature Publishing Group.

Fig. 9

MRI of the cross section of the U87MG tumors implanted in a mouse: (a) without NPs, (b) with the injection of 300 μg of c(RGDyK)–Fe₃O₄ NPs, and (c) with the injection of a blocking dose of c(RGDyK) then c(RGDyK)–Fe₃O₄ NPs; and Prussian blue staining of U87MG tumors in the presence of (d) c(RGDyK)–Fe₃O₄ NPs and (e) a blocking dose of c(RGDyK) and then c(RGDyK)–Fe₃O₄ NPs. Reproduced with permission from ref. 39.

Fig. 10

TEM images of (a) randomly occupied 4 nm/4 nm FePt/Fe₃O₄ array and (b) phase segregated 4 nm/12 nm FePt/Fe₃O₄. Corresponding hysteresis loops (c) and (d) from the binary arrays of (a) and (b) after annealing. TEM image (e) of the annealed composite from (a). Second-quadrant B–H curves of (e) (dot) and annealed 4 nm FePt array (triangle). Reproduced from ref. 44 with permission from Nature Publishing Group.