Biomedical Engineering Reference
In-Depth Information
coFe
2
O
4
and 3-18 nm MnFe
2
O
4
NPs were made by the decomposition of Fe(acac)
3
with co(acac)
2
and Mn(acac)
2
in stoichiometric compositions [34]. The seed-medi-
ated growth was also applied to control the size of these ferrite NPs. M(acac)
2/3
(M = Fe, co, Mn, Zn) can be replaced by the Mcl
2/3
[38], and the thermal decompo-
sition of metal oleate complex can be extended to synthesize MFe
2
O
4
NPs, which
requires the MFe
2
-oleate complex to be prepared in homogeneous fashion, not the
simple mixture of M-oleate and Fe-oleate [39].
a representative composition effect on MRI contrast was demonstrated on 12 nm
MnFe
2
O
4
, Fe
3
O
4
, coFe
2
O
4
, and NiFe
2
O
4
NPs [27]. The NPs were transferred to
aqueous medium by dMSa (Fig. 2.5a). The MnFe
2
O
4
, Fe
3
O
4
, coFe
2
O
4
, and NiFe
2
O
4
NPs show magnetizations of 110, 101, 99, and 85 emu·g
−1
(M + Fe atoms), respec-
tively (Fig. 2.5b). The relevant relaxivities
r
2
were measured to be 358, 218, 172, and
152 mM
−1
·s
−1
at a 1.5
T
MRI scanner, accordingly (Fig. 2.5d). all these NPs outper-
formed the commercial cross-linked iron oxide (clIO), which show a
r
2
at
62 mM
−1
·s
−1
under the same condition (Fig. 2.5d). Most importantly, the Mn-doped
ferrite NPs exhibits the highest magnetization and best contrast sensitivity in
T
2
-
weighted MR image and color-coded MR image. The doping-induced magnetic
modulation is proposed in Figure 2.5c. In MnFe
2
O
4
,
T
sites are occupied by Mn
2+
1-
x
Fe
3+
x
(0 <
x
< 1) and
O
sites are taken by Mn
2+
x
Fe
3+
2-
x
, leading to a magnetic moment
of approximate 5 µ
B
in each unit of MnFe
2
O
4
. This value is estimated to be 4, 3, 2 µ
B
in Fe
3
O
4
, coFe
2
O
4
, and NiFe
2
O
4
because of the complete occupations of M
2+
in their
O
sites. In the image demonstration, the 12nm MnFe
2
O
4
with the best magnetic
properties was modified with the antibody Herceptin, which could specifically target
the HER2/neu marker overexpressed in breast and ovarian cancers. The Herceptin-
conjugated MnFe
2
O
4
(MnMEIO-Herceptin) NPs were tested
in vitro
and compared
with clIO-Herceptin in various cell lines with different levels of HER2/neu over-
expressions: Bx-Pc-3, Mda-MB-231, McF-7, and NIH3T6.7 (Fig. 2.5e). The
much more conspicuous MRI detection sensitivity was found for MnMEIO-
Herceptin conjugates in all cell lines, even in Bx-Pc-3 cell line (low HER2/neu
overexpression), whereas clIO-Herceptin conjugates show negligible signals in
most cell lines.
To further enhance the magnetic property of ferrite, the nonmagnetic Zn
2+
was
doped to form (Zn
x
Fe
1−
x
)Fe
2
O
4
with
x
being controlled from 0 to 0.1, 0.2, 0.3, 0.4,
and 0.8 [38]. With the addition of Zn
2+
,
T
sites were occupied and induced the
partial cancelation of antiferromagnetic coupling between Fe
3+
in
T
and
O
sites,
giving the highest magnetic moment of 161 emu·g
−1
(Zn + Fe atoms) in (Zn
0.4
Fe
0.6
)
Fe
2
O
4
(Fig. 2.6a and b). The higher level of Zn doping caused the drop of magnetic
moment as antiferromagnetic coupling interactions between Fe
3+
ions in each
O
site would be dominant. according to this theory, the maximal
M
s
175 emu·g
−1
(Zn + Mn + Fe atoms) was achieved in the 15 nm (Zn
0.4
Mn
0.6
)Fe
2
O
4
NPs (Fig. 2.6b).
In MRI test under a 4.5
T
field, dMSa-stabilized (Zn
0.4
Mn
0.6
)Fe
2
O
4
NPs and
(Zn
0.4
Fe
0.6
)Fe
2
O
4
NPs exhibit the
r
2
value of 860 and 687 mM
−1
·s
−1
(Fig. 2.6c), a
significant enhancement compared to clIO (62 mM
−1
·s
−1
), Ferridex (110 mM
−1
·s
−1
),
undoped Fe
3
O
4
(276 mM
−1
·s
−1
), and MnFe
2
O
4
(422 mM
−1
·s
−1
) under the identical
condition (Fig. 2.6d) [38].
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