“9.61x6.69” b2815 Tissue Engineering and Nanotheranostics
Magnetic Nanohybrids for Magnetic Resonance Imaging 113
In the synthesis process, bromide used to control the oxidation of
Fe 5 C 2 and 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-
[amino(polyethylene glycol)-2000] (DSPE–PEG–NH 2 ) was applied
on the surface for amine group to link then further. TEM and high
resolution TEM results showed that the Fe 5 C 2 NPs has a core–shell
hybrid structure with a diameter of about 20 nm and the amorphous
carbon layer is behaving as shell.40,42 Magnetization hysteresis loop
shown in Fig. 6(e) illustrates the superparamagnetic behavior of Fe 5 C 2
with a saturation magnetization (Ms) of 125 emu/g at room tem-
pera. Interestingly, carbon layer behave as a protective shell around
the magnetic nanoparticles and Ms loss is less than iron oxide nano-
particles (80 emu/g).^43
Furthermore, Gd-based upconversion paramagnetic core–shell
nanohybrids have been attracting great importance towards biomedical
applications owing to their distinct properties of exchanging near infra-
red light (NIR) to ultraviolet (UV) or visible light via an upconversion
process.^44 More attractive phenomena occurs when photosynthesizer
material layer establishes into upconversion to obtain theranostics
application. Many core–shell nanocomposites materials have been stud-
ied, such as NaYF 4 :Yb/Tm@NaLuF 4 @NaYF 4 @NaGdF 4 ,^45 NaYF 4 :Yb/
Er@NaGdF 4 ,^46 NaLuF 4 :Yb,Tm@NaGdF 4.^47 Gd3+-doped upconversion
magnetic nanoparticles (Gd–UCNPs) can be used for upconversion
luminescent (UCL) imaging and as a T 1 -weighted contrast agent in
MRI, which may enhance the spatial resolution and sensitivity simulta-
neously.48–51 Therefore, the fabrication and development of the multi-
functional core–shell combining Gd–UCNPs with hollow mesoporous
silica nanoparticles are definitely important for the correct diagnosis
and effective therapy of cancer.
Recently, Wu et al. and Shi et al. made great contributions in the
synthesis and application of Gd-based upconversion core–shell
hybrids prepared by simple hydrothermal and thermal decomposition
methods, respectively.52,53 Figure 7(a) is the schematic illustration of
NaGdF 4 :Yb/Tm@SiO 2 @TiO 2 core–shell hybrid structure. Firstly,
they synthesized NaGdF4:Yb/Tm nanoparticles and then used versa-
tile Stober method for silica shell. Finally, TiO 2 -coated on NaGdF 4 :Yb/
Tm@SiO 2 and employed (3-aminopropyl) triethoxysilane (APTES)
