Core-shell structurized Fe3O4@C@MnO2 nanoparticles as pH

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Imaging and Diagnostics

Core-shell structurized Fe3O4@C@MnO2 nanoparticles as pHresponsive T1-T2* dual-modal contrast agents for tumor diagnosis beichen duan, Dongdong Wang, huihui wu, pengping xu, Peng Jiang, Guoliang Xia, Zhenbang Liu, Haibao Wang, Zhen Guo, and Qianwang Chen ACS Biomater. Sci. Eng., Just Accepted Manuscript • DOI: 10.1021/acsbiomaterials.8b00287 • Publication Date (Web): 16 Jul 2018 Downloaded from http://pubs.acs.org on July 21, 2018

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ACS Biomaterials Science & Engineering

Core-shell structurized Fe3O4@C@MnO2 nanoparticles as pH responsive T1-T2* dual-modal contrast agents for tumor diagnosis Beichen Duan,†,# Dongdong Wang,†,# Huihui Wu,§ Pengping Xu,† Peng Jiang,† Guoliang Xia,† Zhenbang Liu,§ Haibao Wang,‡,* Zhen Guo,§,* Qianwang Chen†,∀,*

†

Hefei National Laboratory for Physical Sciences at Microscale, Department of Materials Science & Engineering, University of Science and Technology of China, No.96, JinZhai Road, Hefei, 230026, P. R. China. Email: [email protected].

∀

High Magnetic Field Laboratory, Hefei Institutes of Physical Science, Chinese Academy of Sciences, No.350 Shushanhu Road, Hefei, 230031, P. R. China. Email: [email protected]. §

Anhui Key Laboratory for Cellular Dynamics and Chemical Biology, School of Life Sciences, University of Science and Technology of China, No.96, JinZhai Road, Hefei, 230027, P. R. China. Email: [email protected].

‡

Radiology Department of the First Affiliated Hospital of Anhui Medical University, No.218, Jixi Road, Hefei, 230022, P. R. China. Email: [email protected]. Corresponding Authors: *E-mail: [email protected] (H. Wang). *E-mail: [email protected] (Z. Guo). *E-mail: [email protected] (Q. Chen). Author Contributions: # B.D and D.W. contributed equally to this work.

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ABSTRACT: Biocompatible core-shell Fe3O4@C@MnO2 nanoparticles (named as FOCMO NPs) with an average size at 130 nm prepared through an effortless yet efficient strategy were employed as pH-activatable T1-T2* dual-modality magnetic resonance imaging (MRI) contrast agents (CAs). The release rate of Mn ions in acidic PBS (pH = 5.0) was approximately ten times to that under condition with pH value of 7.4. Benefiting from excellent acid responsiveness, which facilitates the release of ions from FOCMO NPs at tumor region with acidic microenvironment and organelles, the diagnosis accuracy was commendably improved. After intravenous injection of FOCMO NPs, an efficiently intensive contrast in tumors are realized with a distinct enhancement of 127% in T1 MRI signal 24 h after the administration. Moreover, a significant decreasement of 71% are witnessed in T2 MRI signal. Those demonstrated that FOCMO NPs can achieve the purpose of positive/negative MRI simultaneously. Furthermore, obtained FOCMO NPs showed great hemocompatibility and negligible toxicity. KEYWORDS: MRI, contrast agent, dual-modal, pH-responsive, Fe3O4@C@MnO2


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INTRODUCTION Early diagnosis and right disease management, necessitate accurate diagnosis of pathological states of the disease. Magnetic resonance imaging (MRI) was a crucial noninvasive technological means belong to molecular imaging techniques involving computed tomography (CT), fluorescence optical imaging (FOI), ultrasonic imaging (US) and the like.1,2 It can be applied to cancer diagnosis and provide three-dimensional graphic of tissues at a high spatial resolution without radiation harm and penetration depth limitation which has attracted a lot of attentions.3,4,5 Generally, Contrast agents (CAs) are in demand to heighten accuracy of diagnosis. Particularly, CAs have ability in cuting relaxation process of protons to modulate the MR signal.6 Up to now, there have two categories of materials applied, one is paramagnetic gadolinium (Gd)-based coordination complexes which were used to enhance longitudinal relaxation rate as T1 contrast agents.7,8 And usually the other is the superparamagnetic iron oxide NPs, which act on providing negative contrast as T2 CAs.9 Nevertheless, by reason of the low molecular weights, clinical used Gd-based MRI agents usually suffer from short blood circulation time.10 Moreover, the majority of Gd-based CAs have serious system toxicity to organs (kidney and the like).11 While iron oxide-based T2 CAs were limited by the calcification, bleeding, and the susceptibility artifacts.12,7 Just as the facts mentioned above, all the contrast agents now available have more or less drawbacks and limitations. In order to overcome above problems, some dual-modal contrast agents were designed to improve the MRI effect, which provided the integrated imaging information simultaneously.13,14 Not only the T1*-weighted signal provide accurate diagnostic, but also the T2*-weighted signal are contributed to lesions detecting.15 Owing to the MRI signal increased with the aggregation of contrast agents in abnormal tissues, there is a major trend for nanosized contrast agents on occount of the EPR effect. Meanwhile, nano-sized contrast agents have capacity of imaging the pathological characteristics of tumors with low molecular weights. As we all know that the acidic tumor microenvironment is an universal phenomenon, 3 ACS Paragon Plus Environment


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thus preparing pH-responsive nanomaterials can solve the problem the nanoparticles tend to accumulate in the reticuloendothelial system like liver.16 Considering this, Mn2+ with five unpaired electrons may be a good alternative. Since the relaxivity can be largerly increased in response to the interaction between the released Mn2+ and binding proteins, Mn-based systems possess tremendous advantages on contrast amplification among all paramagnetic and magnetic contrast agents.17,18 As reported, over produced H+ in tumor microenvironment can degrade MnO2 and generate Mn2+ to effectively heighten T1-MRI contrast, achieving special diagnosis.19,20 Moreover, water-soluble Mn2+ generated from MnO2 can be excreted by kidneys, so few concerns should be considered about the long-term side effects of MnO2. Herein,

we

demonstrated

a

biocompatible

T1-T2*

dual-modality

MRICA

Fe3O4@C@MnO2 (FOCMO) that high-efficiency magnifies MR signals for the precise imaging of tumors in response to pathological pH. The FOCMO NPs improve relaxivity when MnO2 nanosheets are decomposed into Mn2+ upon reaching acid tumor environment. The synthesis of FOCMO needs only two mild steps. The Fe3O4@C (named as FOC) nanospheres with size at 110 nm are synthesized via a one-step hydrothermal reaction. Obtained carbon coated nanospheres possessed abundant carboxyl on surface. There was a self-sacrificing oxidation-reduction reaction when the as-prepared FOC reacted with the strong oxidizing KMnO4 in aqueous medium, Mn7+ ions were immediately reduced by C = O from carboxyl to MnO2 nanosheets on outer carbon shells. Owing to nonmagnetic MnO2 nanosheets, the saturation magnetization value have decreased by approximately half which were beneficial to increase T1 signal intensity and improve accuracy of T1 MR imaging. Meanwhile, MnO2 nanosheets have excellent pH-responsive release ability, and Mn ions scarcely released in circulation system of neutral condition, which commendably improved T1-T2* dual-modality MR imaging. RESULTS AND DISCUSSION


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Synthesis and characterization of FOCMO. Preparation of FOCMO is implemented via an effictive strategy as shown in Figure 1a. Firstly, the superparamagnetic carbonencapsulated Fe3O4 (FOC) nanospheres with negative charge and carboxyl-functionalized are prepared by means of hydrothermal reaction. Subsequently, reductive carbon shell and Mn7+ ions from KMnO4 aqueous solution induced oxidation-reduction reaction, result in MnO2 grew on outer carbon shells of FOC nanospheres. The scientific experiments are designed through controlling content of added KMnO4 (x mL, x = 0.5, 1.0 and 1.5). Figure 1c-e and g-i showed the SEM/TEM photos of FOCMO coated diverse amount of MnO2, respectively. It revealed that the resultant FOCMO monodispersed NPs were uniform spherical in shape. While amount of KMnO4 increased gradually, the surface of FOCMO NPs got rougher and average size increased from 114 nm to 135 nm, indicating assuredly the reaction between reductive carbon shell and Mn7+ ions. DLS tests are executed to study hydrodynamic size of obtained nanoparticles. Hydrodynamic diameter of pure carbon coated Fe3O4 nanospheres is 130 nm (Figure S1a, Supporting Information). With the increasement of KMnO4 from 0.5 to 1.5 mL, diameter increased from 143 to 179 nm. On the other hand, three samples retained the same core-shell structure. A closer look also revealed the increased thickness of MnO2 shells. DLS curve also revealed that FOCMO guarantee greatly monodisperse and stable PBS solution with mean diameter of 150 nm (Figure S1b). Moreover, the photograph display that FOCMO can maintain stability in both water and PBS solutions for 24 h (Figure S1c). Figure 2a showed the TEM images of FOCMO nanospheres. The high-resolution TEM (HRTEM) images displayed the core-shell nanostructure, in which MnO2 nanosheets grew uniformly on outer shells of carbon coated NPs. Figure 2b-c clearly indicated the lattice fringe spaces of 0.233 and 0.31 nm are corresponding to (101) and (110) planes of the MnO2 phase, respectively. The elemental maps/EDS spectra of optimal FOCMO are shown in Figure 2d-h. Results attested FOCMO NPs own core-shell structure. Evidently, images legibility displayed that the elements Fe/Mn were distributed in core/shell, while O is distributed throughout the 5 ACS Paragon Plus Environment


whole NPs. Besides, the illustrations of EDX analysis spectra corresponding to elemental mapping images indicate that the growth of MnO2 nanosheets on outer shells of carbon coated NPs. XRD patterns (Figure 3a) demonstrated the existence of Fe3O4 and MnO2 according to the published crystal structure data. 21,22 As shown in Figure S2, the diffraction angles of all three groups products centered at 30.1°, 35.4°, 56.9°, 62.5° were identified with JCPDS file 19-0629, Fe3O4. Experimentally obtained weak diffraction peak at 37.3°, 42.8°, 56.6°, 64.8° are indexed to JCPDS file 24-0735, MnO2. The result also indicated that the MnO2 nanosheets had poor crystallinity. XPS measurements of FOCMO NPs show in Figure 3b-c. The Mn 2p spectrum (Figure 3b) of the FOCMO NPs comprised of two symmetrical characteristic peaks (642.46 / 654.03 eV) which were attributable to Mn 2p3/2 and Mn 2p1/2, respectively,23,24,25 and the separation between two peaks was 11.57 eV which was approximately equal to the pure MnO2.23 Additionally, the O 1s spectrum contain three components, strong peak with binding energy at 529.98 eV was attributable to Mn-O bonds in the manganese oxide, peak with binding energy (531.4 eV) is attributable to oxygen in hydroxyl groups radical (Figure 3c).26,27 Besides, the peak (532.5 eV) is assigned to carbonyl groups or adsorbed oxygen.25 It indicated the valence state of MnO2 nanosheets. The FTIR spectra (Figure 3d) of FOC and obtained FOCMO NPs were employed to recognition functional group. The absorption peaks in range of 1360−1720 cm-1 are assigned to double bond stretching / vibrations corresponding to carboxyl group of FOC.23,24 It suggested that the carboxyl were oxidized by KMnO4 owing to the decline of relative intensity. These indicated the core-shell structure of FOCMO. The Raman spectra (Figure 3e) were also operated to confirm the existence of the MnO2 nanosheets. Compared with the spectra of FOC, there was another peak (563 cm-1) observed, attributing to MnO2 nanosheets, and the absorption bands (1720 cm-1) were obviously weaken because carboxyl group reacted with Mn7+ ions. The above results suggested the progressing 6 ACS Paragon Plus Environment

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oxidation-reduction reaction between carboxyl with KMnO4, leading to the growth of MnO2 on surface of FOC nanospheres. Magnetism properties of FOCMO NPs are evaluated by SQUID at 300 K. The Magnetization loops (Figure 3f) showed that both FOCMO NPs and FOC nanospheres maintained the superparamagnetism due to the fact that MnO2 nanosheets were developed on outer shells of carbon coated NPs. In addition, saturation magnetization value (Ms) of FOCMO was 26.67 emu/g, which are obviously smaller on account of the nonmagneticproperties of outer MnO2 nanosheets. The magnetic response ability and dispersibility of as-synthesized FOCMO in deionized water were shown in the illustrations. Products in graph were performed by a magnet side, and the products possessed a larger dispersibility in water when magnet was removed. This results were in accordance with the above analysis and revealed that the as-synthesized FOCMO NPs possessed commendent magnetic response properties and bioapplications. In vitro MRI tests. We further study impact of MnO2 content on magnetic resonance contrast imaging, we detected the longitudinal and transverse relaxation of protons under PBS condition with pH 7.4 respectively. When adding 0.5 mL KMnO4 aqueous solution into FOC, the concentration-normalized values of products were r1 = 2.5422 mM

−1

s

−1

and r2 =

201.9834 mM −1 s −1, while application amounts of KMnO4 aqueous solution increased to 1.0 mL and 1.5 mL, the concentration-normalized values of products were only r1 = 1.3049 mM −1

s

−1

/ 1.2371 mM

−1

s

−1

, and r2 =152.8917 mM

−1

s

−1

/ 141.5947 mM

−1

s

−1

, respectively

(Figure S4). Decreasing relaxation rate is ascribed less unexposed paramagnetic Mn sites with the increasement of thickness of MnO2 shell. And the incremental MnO2 nanosheets caused saturation magnetization of FOCMO NPs decreasing, it resulted in the reduction of T2 contrast effect. Taking consideration of above analysis, FOCMO with 0.5 mL initial KMnO4 solution was used to perform the following experiments. pH- activatable MRI tests. N2 absorption-desorption isotherm (Figure 4a) demonstrated the synthesized FOCMO showed well-defined mesoporous structure. Specific surface area 7 ACS Paragon Plus Environment


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(according to the well-known BET theory) of FOCMO was measured to be 118 m2/g, which was much larger than the surface area of FOC (36.43 m2/g) (Figure S3). As we know, MnO2 is a stable metal oxide in neutral and basic conditions while reduced into Mn2+ under acid environment showing its pH-responsive ability.28 The large surface area would make FOCMO a good candidate for rapid pH-resposive release of Mn ions in acidic environments and simultaneously enhance the T1* relaxation times. To demonstrate the pH-sensitivity of FOCMO, the release experiment of Mn ions from FOCMO was accomplished in different pH values of PBS by means of ICP-AES. In consideration of blood condition and the tumor microenvironment, the pH values of PBS were set as 7.4 and 5.0, respectively. According to the experiment analysis, there was only a little amount of Mn ions released from FOCMO (5.34%) after magnetically stirring 24 h at 37 ℃. Meanwhile, the amount of Mn ions released from the experimental group reached even 47.34%, which performed the same experimental progress in the PBS of pH values 5.0 (Figure 4b). In the light of conclusions mentioned above, it was indicated the products sensitive to the acidic environment, possessing the splendid pH-responsive property. We surveyed the role of FOCMO on MRI to further investigate acid sensitivity of FOCMO NPs with pH values at 7.4, 6.5 and 5.0, respectively (Figure 5). Apparently, there was little impact on MRI in PBS solution with pH value at 7.4, and longitudinal relativity was only 2.1833 mM

−1

s

−1

.

However, when obtained products are dispersed in acid buffer solution with pH value at 5.0, T1 contrast effect obviously enhanced with addition of molar concentration (Mn). Meanwhile, the T1 contrast effect became darker than under PBS (pH 7.4) with equal iron molar concentration. It was pointed that the FOCMO NPs showed the excellent ability to be responsive to pH as positive/negative CAs. Concentration-normalized relaxivity rates were calculated that r1 = 3.5603 mM

−1

s

−1

, r2 = 396.5753 mM

−1

s

−1

under pH = 6.5. When as-

prepared products dispersed in the acid PBS (pH = 5.0), which was similar to tumor microenvironment, the longitudinal relativity was calculated to be 5.3332 mM −1 s −1, and r2 = 8 ACS Paragon Plus Environment

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364.2007 mM

−1

s

−1

, suggesting as-synthesized NPs have enough sensitivity to acidic

environment, which are able to serve as great T1-T2* dual-modality CA. Meanwhile, the longitudinal relativity of synthesized NPs is 5.3332 mM

−1

s

−1

obviously superior to some

Mn-based MRI agents at acidic environment, such as manganese-doped hollow mesoporous silica NPs (0.76 mM −1 s −1) and FeMn(SiO4) hollow nanospheres (1.92 mM −1 s −1). 29,30 Cytotoxicity assay. For subsequent applications, assessing cytotoxicity of assynthesized NPs is crucial. HeLa and 4T1, which were cultured with different concentrations (0, 12.5, 25, 50, 100, 200 µg/mL) of FOCMO NPs for 24 h by MTT, were used to estimate the cytotoxicity. Both HeLa and 4T1 cell showed a high cell viability (> 85%) even at a concentration of 200 ppm after incubation 24 h (Figure 6). This revealed that FOCMO NPs have no apparent toxicity owing to the release of Mn ions from FOCMO NPs surface into the acidic organelles through endocytosis.31 Furthermore, the NPs were stable in neutral blood and normal tissues on account of the fact that Mn is the essential element in organisms.32 Biocompatibility of FOCMO NPs. We next verified whether FOCMO own remarkable biocompatibility. Considering that CAs will be circulated through the blood circulation system, so it is essential that those CAs should possess good hemocompatibility.33 We performed the hemocompatibility test of as-synthesized FOCMO by hemolysis assay using UV-vis spectrophotometer. After incubating mixture (RBCs and FOCMO) 3 h at 37 ℃, the UV-vis spectra were demonstrated in Figure S5. We measured absorbance of the supernatant (541 nm), there were no evident absorption peaks be detected for all products with different concentrations in the range of 0-800 ppm compared to that of water. We also calculated the hemolytic percentages of FOCMO NPs by the OD at 541 nm (Figure 7a). It was a remarkable fact that the hemolysis percentage of FOCMO NPs was less than 7% even at a high concentration of 800 ppm, which verified that the FOCMO NPs possess excellent hemocompatibility. Also as shown in the illustrations (Figure 7a), a slight black observed in



the print of the supernatant for the 800 ppm FOCMO solution, of course, other samples likewise can observe negligible red color. We used Balb/c nude mice to further verify the biocompatibility of FOCMO NPs in vivo bio-distribution. After injecting a right dose of NPs into the health mice 24 h later, FOCMO NPs were delivered to the surrounding tissues along with captured by some organs through blood circulation,34 and then the major organ such as liver, kidney, spleen, stomach, heart, lung were immediataly obtained to measured the iron concentration by ICP-AES. In the light of calculation of iron content in above tissues (Figure 7b), the consequence revealed that the irons primally distributed in the liver with high mononuclear phagocytic activity. Also, liver was primary organ to clear FOCMO NPs by biodegradation.35,14 Therefore, we can draw a conclusion that FOCMO NPs are primally endocytosed by liver through reticuloendothelial system (RES).36,37 After administration of saline and the FOCMO NPs, histological analyses are performed to further shed light on the biocompatibility of FOCMO. Six main organs are stained by hematoxylin and eosin. It showed the whole organs possess integrity cell structure in tissue morphology compared with the control group (Figure 7c). In conclusion, the FOCMO NPs have good biocompatibility. In vivo MRI tests. We selected randomly mice to assess the MRI dual-modal contrast effect in vivo via intravenous injection of the fixed dosage (3 mg/kg Mn ions) of FOCMO NPs using a 3T MR scanner. According to the date of pre-injection and after administration of FOCMO at 30 min, 1 h, and 24 h collected from liver and kindey. As shown in Figure 8a, it can be observed that the signal of T1*-weighted MRI augment and brighten significantly, while the T2 signal remarkably darken compared with the pre-injection images (Figure 8b). The phenomenon was result from the as-synthetic large particle size (>10 nm) of FOCMO, which were usually endocytosed and cleared through RES,34,36 corresponding with the biodistribution result. Since the T1-T2* dual-modal contrast agents FOCMO NPs was capable to improve relaxation of protons, we quantify contrast effect in defined regions of liver, the 10 ACS Paragon Plus Environment

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quantitative analysis displayed that the T1 signal intensity increased approximately 27% after intravenous injection 24 h compared with the pre-injection (Figure 8c), it was larger about 21% in T1 imaging compared with Mn-HMSNs.29 Meanwhile, the T2 signal intensity was weaken to 71% (Figure 8d). The consequences show the FOCMO had unique dual-modal MRI effect to enhance the T1-T2*-weight contrast simultaneously. And benefiting from excellent acid sensitivity, FOCMO contribute to distinguish lesions and improve the accuracy of cancer diagnosis. Furthermore, the FOCMO NPs showed great hemocompatibility and negligible toxicity without side effects, which distinguished from the harmful Gd-based MRI agents. CONCLUSIONS Core-shell structured FOCMO are fabricated in situ via a self-reduction strategy. Through coating MnO2 onto outer shells of carbon coated nanoparticles, the resulting FOCMO NPs can not only be served as pH-activatable T1-T2* dual-modality CAs. Cytotoxicity assays, hemolysis assay, histology analysis demonstrated FOCMO NPs possess negligible toxicity and remarkable biocompatibility. In vivo MRI tests showed evident distinction between the normal tissues and tumors through synergistic T1 and T2* signals. On the other hand, FOCMO NPs possess excellent hemocompatibility and non-toxicity even at a high concentration of FOCMO NPs for long hours. Therefore the FOCMO is a safty dualmodal contrast agent for precisely diagnosis, will be promisingly conducive to multiplex diagnostic nanoplatform. ASSOCIATED CONTENT Supporting Information Additional experimental details, DLS data, powder X-ray diffractions, BET surface area, MRI test, UV-vis absorbance spectrum (Figure S1-S5, PDF). Corresponding Authors *E-mail: [email protected] (H. Wang). 11 ACS Paragon Plus Environment


*E-mail: [email protected] (Z. Guo). *E-mail: [email protected] (Q. Chen). Author Contributions #

B.D and D.W. contributed equally to this work.

Notes The authors declare no competing financial interest. ACKNOWLEDGEMENTS We thank Core Facility Center for Life Sciences of University of Science and Technology of China for imaging support. This work was supported by the National Natural Science Foundation of China, 21571168(QW. Chen), The Most Grant 2016YFA0101202 (Z. Guo), U1232211 (QW. Chen). REFERENCES (1) Schima, W.; Mukerjee, A.; Saini, S. Contrast-enhanced MR imaging. Clin. Radiol. 1996, 51 (4), 235-244. (2) Caravan, P.; Ellison, J. J.; McMurry, T. J.; Lauffer, R. B. Gadolinium(III) chelates as MRI contrast agents: Structure, dynamics, and applications. Chem. Rev. 1999, 99 (9), 2293-2352. (3) Chen, Y.; Li, M.; Hong, Y.; Lam, J. W.; Zheng, Q.; Tang, B. Z. Dual-modal MRI contrast agent with aggregation-induced emission characteristic for liver specific imaging with long circulation lifetime. ACS Appl. Mater. Interfaces 2014, 6 (13), 10783-10791. (4) Huang, Y.; Hu, L.; Zhang, T.; Zhong, H.; Zhou, J.; Liu, Z.; Wang, H.; Guo, Z.; Chen, Q. Mn3[Co(CN)6]2@SiO2 core-shell nanocubes: novel bimodal contrast agents for MRI and optical imaging. Sci. Rep. 2013, 3, 2647. (5) Mahmoudi, M.; Serpooshan, V.; Laurent, S. Engineered nanoparticles for biomolecular imaging. Nanoscale 2011, 3 (8), 3007-3026. (6) Zhen, Z.; Xie, J. Development of manganese-based nanoparticles as contrast probes for magnetic resonance imaging. Theranostics 2012, 2 (1), 45-54. 12 ACS Paragon Plus Environment

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Figures

Figure 1. Synthesis of Fe3O4@C@MnO2 (FOCMO) NPs. (a) Schematic illustration of following fabrication of FOCMO NPs with 0.5 , 1.0 and 1.5 mL KMnO4; (b-e) SEM of FOC/ FOCMO NPs prepared with 0.5, 1.0 and 1.5 mL KMnO4, respectively; (f-i) TEM of FOC/FOCMO NPs prepared with 0.5, 1.0 and 1.5 mL KMnO4, respectively.



Figure 2. (a-c) TEM and HRTEM photos of FOCMO; (d) HADDF-STEM image and EDX line analysis spectra; (e-h) The corresponding EDX element mapping (Fe, Mn and O) and merged images of FOCMO NPs.


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Figure 3. Characterization of FOCMO NPs. (a) X-ray diffraction patten of FOCMO NPs; (b) and (c) XPS spectra of the Mn2p and O1s, respectively; (d) FTIR spectra of FOCMO/FOC nanospheres; (e) Raman spectra of FOCMO/FOC; (f) Magnetic properties of FOC/FOCMO. The insets in panel are photographs of aqueous FOCMO NPs dispersity (i), next to external magnetic field (ii) and removed the magnet 5 min later (iii).



Figure 4. (a) Nitrogen adsorption-desorption isotherms and corresponding pore size distribution of FOCMO NPs; (b) Release of Mn ions from FOCMO in different PBS.


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Figure 5. In vitro MRI of FOCMO in PBS at pH 7.4, 6.5 and 5.0. (a-b) MRI phantom images of FOCMO NPs at different Mn and Fe concentrations, respectively; (c) normalization of r1*, (d) normalization of r2* at different pH conditions.

Figure 6. In vitro cytotoxicity of FOCMO NPs to HeLa and 4T1 cells. 21 ACS Paragon Plus Environment


Figure 7. Biocompatibility of FOCMO NPs. (a) Hemocompatibility of FOCMO under different concentrations (Inset photos were visualized experimental phenomena); (b) In vivo bio-distribution after intravenous injection of FOCMO NPs 24 h later; (c) Histological analysis of six primary organs of saline treated (control) and FOCMO treated mice one whole day later (every scale bars are 50 µm).


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Figure 8. In vivo MRI. (a) T1, (b) T2 MRI of HeLa tumor-bearing mice at different time postinjection of FOCMO NPs (top are transverse planes and bot tom are coronal planes; tumor, liver and kidney are circled with red, green and yellow lines, respectively); (c) and (d) Quantification analysis of relative T1-weighted and T2-weighted MRI signal intensity at different time, respectively.



For Table of Contents Use Only Core-shell structurized Fe3O4@C@MnO2 nanoparticles as pHresponsive T1-T2* dual-modal contrast agents for tumor diagnosis Beichen Duan, Dongdong Wang, Huihui Wu, Pengping Xu, Peng Jiang, Guoliang Xia, Zhenbang Liu, Haibao Wang*, Zhen Guo*, Qianwang Chen*


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Core-shell structurized Fe3O4@C@MnO2 nanoparticles as pH

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