Iron Oxide-Based Magnetic Nanoparticles Synthesized from THE Organic Solution Phase for Advanced Biological Imaging - Nanotechnology for Biomedical Imaging and Diagnostics - page 38

The au shell was formed on the surface of Fe 3 O 4 NPs after the addition of Haucl 4 to
the chloroform solution and the slow reduction of Haucl 4 by oleylamine. The pro-
duced Fe 3 O 4 /au core-shell NPs were dispersed in hexane and also in aqueous
medium after ligand exchange with hexadecyltrimethylammonium bromide and
sodium citrate. The Fe 3 O 4 /au core-shell NPs could further act as seeds to obtain
Fe 3 O 4 /au (thicker shell) and Fe 3 O 4 /au/ag NPs, where the shell thickness was tuned
by seed/precursor ratio [50].
dumbbell-like Fe 3 O 4 /au NPs represent another class of hybrid dual-functional
probe. The growth toward dumbbell NPs requires exquisite control in the solvent
choice, precursor concentration, and reaction temperature in favor of heterogeneous
nucleation. as shown in Figure 2.8a, the decomposition of Fe(cO) 5 initiates the
nucleation over the surface of au seeds and air oxidizes Fe into Fe 3 O 4 [51]. The size
of the Fe 3 O 4 part is controlled by the ratio of Fe(cO) 5 /au seeds. The dumbbell NPs
have two different types of surface, making the surface modification with different
targeting and drug molecules much easier in comparison to single component NPs
(Fig. 2.8b and c) [52, 53]. as an example, Fe 3 O 4 surface was linked to dopamine-
PEg-NH 2 through the chelating catechol unit in dopamine to Fe 3 O 4 . The au surface
was modified by SH-PEg-NH 2 via the formation of au/S bonding. The water-soluble
au/Fe 3 O 4 NPs with amine group was further conjugated with epidermal growth factor
receptor antibody (EgFRa) for their targeting a431 human epithelial carcinoma cells
that overexpress the epidermal growth factor receptor (Fig. 2.8d) [52]. In vitro exper-
iments show that the EgFRa-labeled 8-20 nm au/Fe 3 O 4 dumbbell NPs had high
specificity to a431 cells with a r 2 of 80.4 mM −1 ·s −1 at a 3 T field (Fig. 2.8e). Meanwhile,
the a431 cells labeled with 8-20 nm au/Fe 3 O 4 NPs could also be monitored with a
scanning confocal microscopy (Fig. 2.8f). Using the wavelength of 594 nm to detect
the strong reflectance from au, the morphology of a431 cells was clearly visualized.
More importantly, there was no image intensity change even after 3 days, providing a
long-term optical tracking of the cells in addition to MRI detection.

2.5.2 MrI + computed tomography

x-ray computed tomography (cT) is a powerful and widely used clinical imaging
modality, which can offer high-resolution 3d tomography information of the ana-
tomic structure. But it has relatively low sensitivity, which is disadvantageous in
diagnosing soft tissue [54, 55]. MRI with high sensitivity can be combined with cT
to achieve more accurate detection. The first reported NP-based MRI-cT dual-func-
tional contrast agent is FePt NPs, where FePt NPs are superparamagnetic and Pt has
a strong x-ray absorption [54]. Relevant in vivo tests have demonstrated that the FePt
NPs have potential to enhance the MRI T 2 contrast and cT contrast simultaneously.
Recently, core-shell Fe 3 O 4 /TaO x NPs were tested for simultaneous MRI-cT dual
detection [55]. Figure 2.9a summarizes the synthesis of this class of core-shell NPs.
a Fe 3 O 4 core is premade and stabilized with oleic acid and then further transferred
into reverse micelles after mixing with cyclohexane, ethanol, IgEPal cO-520, and
NaOH. The TaO x shell is formed through sol-gel reaction of tantalum ethoxide over
the surface of Fe 3 O 4 NP core. Subsequently, the sol-gel reaction can also be utilized
to modify the core-shell NPs with PEg-silane and rhodamine B isothiocyanate