Biomedical Engineering Reference
In-Depth Information
Fe/MnFe
2
O
4
NPs with a relaxivity of 356 mM
−1
·s
−1
produced the same contrast effect
at 10 times lower dose compared to clIO and displayed better MRI sensitivity than
single component ferrite NPs (Fig. 2.7b) [41].
The single-crystalline
bcc
-Fe/
fcc
-Fe
3
O
4
NPs with further enhanced magnetization
were also synthesized by the decomposition of Fe(cO)
5
in the presence of oleyl-
amine and hexadecylamine chloride [43]. The use of hexadecylamine chloride was
critical for the formation of single-crystalline
bcc
-Fe NPs. after exposure to air, a
shell of crystalline Fe
3
O
4
was formed (Fig. 2.7c). The 10.5 nm core/2.5 nm shell bcc-
Fe/
fcc
-Fe
3
O
4
NPs displayed a very stable magnetization of 164 emu·g
−1
(Fe), much
higher than 16 nm amorphous Fe/
fcc
-Fe
3
O
4
NPs and Fe
3
O
4
NPs. Therefore, a darker
T
2
-weighted MR image was visualized with bcc-Fe/
fcc
-Fe
3
O
4
NPs (Fig. 2.7d). In
biological test, the 15 nm
bcc
-Fe/
fcc
-Fe
3
O
4
NPs were stabilized by oleylamine-PEg
and show a relaxivity
r
2
of 220 mM
−1
·s
−1
at a 3
T
field, better than Ferridex
(110 mM
−1
·s
−1
) and comparable with the MnFe
2
O
4
NPs stabilized by dMSa with
2 nm coating thickness. It is noteworthy that the
r
2
value of
bcc
-Fe/
fcc
-Fe
3
O
4
is mea-
sured with the influence of thick coating (around 15 nm).
2.5 desIgns and faBrIcatIons of MultIModalIty IMagIng
agents Based on IoMnps
The intrinsic “dark”
T
2
-weighted contrast image given by IOMNPs sometimes causes
ambiguity with hypointense area in the practically clinical detection, such as bleeding,
calcification, and metal deposition [6]. To address this issue, the multimodality
imaging combining MRI with other imaging modality has been studied to enhance
the diagnostic accuracy. For instance, the conjugate of MnFe
2
O
4
with
124
I through
the reaction between
124
I and a surface functional group of NPs can be used as MRI-
positron emission tomography (PET) dual-modality contrast agent [44]. The surface
of IOMNPs can be modified by some organic dye to enable the MRI-fluorescence
dual imaging [45-48]. But the multistep surface conjugating reaction may lead to
degradation/leaking of surface conjugates, decrease in efficiency, and increase in
toxicity. In this section, we focus on fabrications of multimodality imaging agents
based on hybrid inorganic IOMNPs where other inorganic components are crystallo-
graphically attached to iron oxide in the structure such as core-shell and dumbbell.
2.5.1
MrI + optical Imaging
a variety of optically active inorganic materials have been successfully loaded onto
the surface of IOMNPs, forming a core-shell structure. The Fe
3
O
4
/ZnO core-shell
NPs were made by a two-step thermal decomposition of Fe(acac)
3
and of Zn(acac)
2
in octyl ether [49]. The Fe
3
O
4
/ZnO core-shell NPs show dual superparamagnetic and
fluorescent properties and could be detected
in vitro
by confocal microscopy and
in vivo
by MRI [49]. another example is Fe
3
O
4
/au core-shell NPs in which the au
shell is a plasmonically active component [50]. The Fe
3
O
4
NP seeds were first pre-
pared through thermal decomposition and dispersed in chloroform with oleylamine.
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