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HAMAFA-b-DBAM-coated SPIONPs, confirming the capa-
bility of the SPIONP core in enhancing the transverse proton
relaxation process. Fig. 6b shows the relaxation rate, the specific
relaxivities are 4.9 and 163 mMꢀ1 sꢀ1 for r1 and r2, respectively.
The relaxivity of r2/r1 is an important aspect to evaluate the
efficiency of T2-contrast agent. In our approach, r2/r1 is calcu-
lated to be 33, which is much larger than that of dextran-coated
SPIONPs.43
8 R. Hao, R. Xing, Z. Xu, Y. Hou, S. Gao and S. Sun, Adv. Mater.,
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To further evaluate the degradation influence to the nano-
composites, magnetic resonance phantom imaging was used. The
intensity of the colloid showed a significant T2-weighted intensity
drop-off in an acidic environment (pH ¼ 5.0) in comparison to the
control ([Fe] ¼ 8.38 ꢂ 10ꢀ4 mg mLꢀ1), which exhibited high sensi-
tivity and rapid detectability by MRI. The T2-weighted images of the
nanocomposites before and after acidification are shown in Fig. 6c
and the T2-weighted intensity was calculated using a built-in soft-
ware. In addition, about 52% of the T2 intensity decrease was
observed after acidification for 4 h, consistent with the above
assumptions. The decrease in T2-weighted intensity is probably
attributed to the partial aggregation of hydrophobic SPIONPs. In
acidic condition, the drug is released and then the hydrophobic
SPIONPs aggregate resulting in MR sensitivity increase.44–46 In
addition, MR imaging was further used to confirm the targetability
of HAMAFA-b-DBAM-coated SPIONPs. The T2-weighted MR
image (Fig. S5†) of KB cells incubated with HAMAFA-b-DBAM-
coated SPIONPs showed an obvious negative contrast enhancement
in comparison to the HAMA-b-DBAM-coated SPIONPs, which
revealed effective nanocomposites internalization inside the KB cells.
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nanoparticles and chemotherapeutic agent doxorubicin with
a
biodegradable pH-activated polymeric carrier, we can
construct a multifunctional nanocomposite that enables selective
magnetic resonance imaging and anticancer therapy. Folic acid
was also conjugated on the polymeric carrier as the targeting
moiety. The obtained biocompatible and water-stable
HAMAFA-b-DBAM-coated SPIONP colloids can directionally
image and release in a mildly acidic pathological site via
a degradation and aggregation process, which can provide
a promising potential application for early detection and therapy
of some cancers.
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Acknowledgements
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This work was supported by the National Natural Science
Foundation of China (Grant Nos. 20876101, 20902065,
21071105 and 21076134), the Natural Science Foundation of the
Jiangsu Higher Education Institutions of China (Grant
No.09KJB430010) and Innovative Research Team of Advanced
Chemical and Biological Materials, Suzhou University.
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This journal is ª The Royal Society of Chemistry 2011
J. Mater. Chem., 2011, 21, 12682–12690 | 12689