Microwave assisted fast fabrication of Fe3O4-MWCNTs nanocomposites and their application as MRI contrast agents

Microwave assisted fast fabrication of Fe3O4-MWCNTs nanocomposites and their application as MRI contrast agents

Materials Letters 67 (2012) 49–51 Contents lists available at SciVerse ScienceDirect Materials Letters journal homepage: www.elsevier.com/locate/mat...

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Materials Letters 67 (2012) 49–51

Contents lists available at SciVerse ScienceDirect

Materials Letters journal homepage: www.elsevier.com/locate/matlet

Microwave assisted fast fabrication of Fe3O4-MWCNTs nanocomposites and their application as MRI contrast agents Yuxin Chen, Hongchen Gu ⁎ Nano Biomedical Research Center, School of Biomedical Engineering and Med-X Research Institute, Shanghai Jiao Tong University, Shanghai, 200030, China

a r t i c l e

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Article history: Received 12 July 2011 Accepted 8 September 2011 Available online 17 September 2011 Keywords: Fe3O4 Carbon nanotubes Nanocomposites Microwave MRI contrast agents

a b s t r a c t Uniform Fe3O4 nanoparticles with diameters of 3–5 nm are successfully decorated onto the external walls of multiwall carbon nanotubes (MWCNTs) by in situ high-temperature decomposition of Fe(acac)3 in polyol solution under the irradiation of microwave. With this method, reaction time of forming Fe3O4-MWCNTs nanocomposites has been significantly shortened to 15 min. The resulting Fe3O4-MWCNTs nanocomposites show superparamagnetic property at room temperature and can be remained as stable aqueous dispersion for 2 months. Longitudinal relaxivity (r1) and transverse relaxivity (r2) of the magnetic MWCNTs are 8.34 Fe mM−1 S−1 and 146 Fe mM−1 S−1 respectively. The much higher r2 value and the obvious change in the gray scale of MR images confer the Fe3O4-MWCNTs nanocomposites as potential candidates for T2-weighted MRI contrast agents. © 2011 Elsevier B.V. All rights reserved.

1. Introduction Carbon nanotubes(CNTs) decorated with Fe3O4 nanoparticles on their external surface have been intensely studied recently due to their exceptional performances and potential applications in various fields such as cancer diagnostic and treatment [1–4], targeted drug delivery [5], catalyst [6,7], reinforcing materials [8], electrodes [9], wastewater treatment [10], etc. Several methods have been explored to attach Fe3O4 nanoparticles onto CNTs, among which in situ chemical deposition of Fe3O4 nanoparticles onto CNTs is relatively more universal and effective [11–15]. Liu et al. have deposited a series of magnetic ferric MFe2O4 (M= Fe, Co, Ni) nanoparticles onto MWCNTs by in situ hightemperature hydrolysis and inorganic polymerization of metal salts in TREG solution [14]. Zhang et al. also have decorated MWCNTs modified by polyethyleneimine (PEI) with Fe3O4 nanoparticles fabricated in Teflon-lined stainless steel autoclave at 200 °C for 12 h [15]. Nevertheless, all these approaches for preparing the Fe3O4-MWCNTs nanocomposites often require several hours, and the binding efficiency of Fe3O4 nanoparticles onto MWCNTs remained quite low. Consequently, there is an urgent need to develop new techniques for rapid and efficient synthesis of the Fe3O4-MWCNTs nanocomposites. Herein, we demonstrate a novel, rapid and effective route for decoration of MWNTs with uniform Fe3O4 nanoparticles via microwave induced high-temperature decomposition of Iron (III) precursor in polyol liquid. The deposition time was dramatically reduced to 15 min, and the resulting nanocomposites perform excellent water-dispersible and

⁎ Corresponding author. Tel.: + 86 21 62933176; fax: + 86 21 62933743. E-mail address: [email protected] (H. Gu). 0167-577X/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2011.09.042

superparamagnetic properties. The MRI relaxivity was measured to explore the potential for the application of MRI contrast agents. 2. Experimental 2.1. Materials MWNTs (diameters of 20–40 nm, purity above 95 wt.%) were provided by Shenzhen Bill Technology Development Co. Ltd (China). Iron (III) acetylacetonate (Fe(acac)3, purity above 99 wt.%) was purchased from Acros. Ultra purity water (18.2 MΩ cm−1) was obtained from a PURELAB Plus water purification system (ELGA, UK). All other chemicals used were analytical grade and from SinoPharm Chemical Reagent Co. Ltd. 2.2. Synthesis of Fe3O4-MWNTs nanocomposites For purification and functionalization of MWCNTs, pristine MWCNTs dispersed in the mixed solution of concentrated sulfuric and nitric acids (1:1 by volume) was processed in Focused Microwave Synthesis system (Discover S-Class, CEM) at 100 °C for 20 min under high level stirring. After the reaction, the MWCNTs were centrifuged and washed with ultra pure water until the pH value reached neutral, followed by a final drying overnight in vacuum at 55 °C for further use. The purified and functionalized MWCNTs are symbolized as pf-MWCNTs below. For deposition of Fe3O4 nanoparticles, 10 mg pf-MWCNTs was added into 5 mL TREG solution by ultrasonication for 5 min. Then 10 mg Fe(acac)3 was added to form a stable solution. After that, the stable solution was subjected to microwave irradiation in a 10 mL closed-vessel reaction chamber lined with Teflon PFA under vigorous stirring at 200 °C for 15 min without extra pressure. After cooled to

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room temperature, the sample was purified by centrifuging with ethanol for several times and freeze–dried in vacuum. 2.3. Characterization The pf-MWCNTs were characterized by transmission electron microscopy (TEM, JEOL-JEM2010). The Fe3O4-MWCNTs nanocomposites were investigated by transmission electron microscopy (TEM, JEOLJEM2010), X-ray diffraction (XRD, Dmax-r C X-ray diffractometer 40 kV and 100 mA, Rigaku) using Cu-Kα radiation, vibrating sample magnetometer (VSM, Lake Shore-7404). Fe concentrations of the Fe3O4-MWCNTs colloid were measured with Inductively Coupled Plasma Optical Emission Spectrometer (ICP, Thermo Scientific, Iris Advantage 1000). A series of longitudinal relaxation times (T1) and transverse relaxation times (T2) of the Fe3O4-MWCNTs colloid with different concentrations were measured by NMR spectrometer (Minispec, mq60, Brucker) with t1-sr-mb and t2-cp-mb sequences. MR Imaging of the Fe3O4-MWCNTs colloid with the concentrations ranging from 0.125 to 2 mM in water was performed on a 3 T MR scanner (Magnetom Avanto, Siemens AG, Erlangen, Germany) by using a T2-weighted spinecho sequence (TE= 51 ms, TR= 5000 ms). 3. Results and discussion As shown in Fig. 1a, pristine MWCNTs aggregate into bundles with many impurities adhering on their surface. Severe precipitation of pristine MWCNTs in water occurred within 2 days (vial A in Fig. 1c). The pf-MWCNTs have been debundled into individual tubes or very thin bundles (Fig. 1b). The pf-MWCNTs are highly dispersible in water under ambient conditions to produce a stable aqueous solution which showed no obvious indication of precipitation within 2 months (vial B in Fig. 1c).This result indicates that the MWCNTs are successfully purified and functionalized with plenty of functional groups such as carboxyl, carbonyl and hydroxyl groups serving as active sites for the coupling of Fe3O4 nanoparticles [16,17]. As could be seen from Fig. 1d and e, the MWCNTs have been uniformly coated with Fe3O4 nanoparticles of which diameters are 3– 5 nm within barely 15 min. Moreover few free Fe3O4 nanoparticles are observed though the Fe3O4-MWCNTs nanocomposites were washed and ultrasonicated repeatedly during the purification process. From the HRTEM image (Fig. 1f), it can be found that the Fe3O4

nanoparticles are single crystalline and the distance between two adjacent planes is approximately 0.25 nm, which is in accordance with the (311) lattice plane in the inverse spinel-structured Fe3O4 nanoparticles. A lattice spacing of about 0.34 nm in the MWCNTs walls can also be resolved, which corresponds to the interlayer spacing of the MWCNTs [13]. In our work, with Fe(acac)3 as the iron precursor, the reaction temperature was lowered and the reaction time was sharply reduced to only 15 min under the irradiation of microwave. The as-synthesized Fe3O4-MWCNTs nanocomposites can be easily dispersed in water without any addition of surfactants, and the colloid remains stable for 2 months (vial C in Fig. 1c). Fig. 2a illustrates the XRD patterns of the pf-MWCNTs (inset) and the pf-MWCNTs deposited with magnetite nanoparticles. It can be seen that the diffraction peaks at 25.98° and 42.78° are ascribed to (002) and (100) planes of the pf-MWCNTs. After decoration of magnetite nanoparticles to the pf-MWCNTs, six new peaks at 30.00°, 35.48°, 43.14°, 53.44°, 57.04° and 62.58° are observed, which matched well with the (220), (311), (400), (422), (511) and (440) planes of the standard XRD data for the cubic Fe3O4 phase of inverse spinel crystal structure (JCPDS file No. 19-0629). No peaks corresponding to impurities are detected. These results revealed that the magnetic MWCNTs decorated with magnetite nanoparticles have been successfully obtained during the preparation process. The magnetic property of the Fe3O4-MWCNTs nanocomposites was investigated by VSM. As illustrated in Fig. 2b, the sample exhibit superparamagnetic behavior at 300 K without detectable coercivity and remanence because the size of our Fe3O4 nanoparticles (3–5 nm) are much smaller than the room temperature superparamagnetic critical size of Fe3O4 (25 nm) [18]. The magnetic saturation of 9.19 emu/g is lower than that of corresponding pure bulk Fe3O4 (93 emu/g) [19], which is mainly attributed to the existence of large portion of MWCNTs in the nanocomposites and the very small sizes of the Fe3O4 nanoparticles. Relaxivity (r1,2) represents the enhancement efficiency of MRI contrast for the contrast agents, which is defined in the Eq. (1) [20]: 1=T1;2;susp ¼ 1=T1;2;water þ r1;2 CFe

ð1Þ

where 1/T1,2,susp is the relaxation rate of the Fe3O4-MWCNTs colloid, 1/T1,2,water is the relaxation rate of water, CFe is the Fe concentration of the Fe3O4-MWCNTs colloid. As shown in Fig. 3a, 1/T1 and 1/T2 relaxation rates both varied linearly with iron concentrations, and

Fig. 1. Representative TEM images of (a) pristine MWCNTs, (b) pf-MWCNTs treated in concentrated mixture of acids assisted with microwave at 100 °C for 20 min; (c) photograph of pristine MWCNTs dispersed in water 2 days after ultrasonicated for 5 min (vial A), the pf-MWCNTs dispersed in water 2 months after treated (vial B) and the Fe3O4-MWCNTs nanocomposites dispersed in water for 2 months since fabricated (vial C); representative TEM images of (d, e) the Fe3O4-MWCNTs nanocomposites obtained with an initial Fe (acac)3:MWCNTs weight ratio of 1:1 in TREG solution at 20 °C for 15 min; (f) HRTEM images of the Fe3O4-MWCNTs nanocomposites.

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Fig. 3. (a) 1/T1 and 1/T2 relaxation rates plotted against the Fe concentration for the Fe3O4-MWCNTs colloid; (b) T2-weighted MR imaging of the Fe3O4-MWCNTs colloid with different Fe concentrations (from left to right, the Fe concentration is 0.125 mM, 0.25 mM, 0.5 mM, 1 mM, 2 mM respectively).

Acknowledgments Fig. 2. (a) XRD patterns of the Fe3O4-MWCNTs nanocomposites and pf-MWCNTs (inset); (b) Magnetization curves of the Fe3O4-MWCNTs nanocomposites at 300 K.

longitudinal relaxivity (r1) and transverse relaxivity (r2) are 8.34 Fe mM −1 S −1 and 146.46 Fe mM −1 S −1 respectively. Comparing with clinical used superparamagnetic iron oxide (SPIO) contrast agent Feridex [21], which has transverse relaxivity (r2) of 110 Fe mM −1 S −1, our Fe3O4-MWCNTs nanocomposites possess much stronger transverse contrast enhancement. Furthermore, the T2-weighted MR images change obviously in gray scale with Fe concentrations (Fig. 3b), indicating that the as-synthesized Fe3O4-MWCNTs nanocomposites generate MR contrast enhancement on T2-weighted MR imaging. The much higher r2 value and the obvious change in the gray scale of MR images confer the Fe3O4-MWCNTs nanocomposites as potential candidates for T2-weighted MRI contrast agents. The same conclusion of high MR contrast enhancement has been drawn in some reported works [4,22,23]. Compared to these reported results, our synthesis process is much more effective. Furthermore, the magnetic nanotubes were proved to be with low cytotoxicity, neglectable hemolytic activity and high cell-labeling efficiency.

4. Conclusions In summary, we have developed a novel microwave irradiation method to chemically deposit uniform Fe3O4 nanoparticles with diameters of 3–5 nm onto MWCNTs. The processing time has been shortened to 15 min through microwave induced reaction. The assynthesized Fe3O4-MWCNTs nanocomposites exhibit superparamagnetic property and can be stably dispersed in water for 2 months. Moreover, the higher relaxation performance and the stronger contrast enhancement of MR imaging for the Fe3O4-MWCNTs nanocomposites verified them as potential candidates for T2-weighted MRI contrast agents.

This work was supported by MOST project (2009AA03Z333), NSFC Funding (30870706), Shanghai Nano Project (1052nm01100) and SJTU Funding (YG2010ZD102, YG2009ZD203). The authors would like to thank the Instrumental Analysis Center of Shanghai Jiao Tong University for Materials Characterization. The authors also gratefully acknowledge Dr. Dan Li and Prof. Jiang Lin for Magnetic Resonance Imaging in ZhongShan Hospital of Fudan University. References [1] Yang F, Hu JH, Yang D, Long J, Luo GP, Jin C, et al. Nanomedicine 2009;4(3): 317–30. [2] Yang F, Jin C, Yang D, Jiang YJ, Li J, Di Y, et al. Eur J Cancer 2011;47:1873–82. [3] Gul H, Lu WB, Xu P, Xing J, Chen J. Nanotechnology 2010;21:155101. [4] Bai X, Son SJ, Zhang SX, Liu W, Jordan EK, Frank JA, et al. Nanomedicine 2008;3(2): 163–74. [5] Yang D, Yang F, Hu JH, Long J, Wang CC, Fu DL, et al. Chem Commun 2009;29: 4447–9. [6] Nigrovski B, Zavyalova U, Scholz P, Pollok K, Muller M, Ondruschka B. Carbon 2008;46:1678–86. [7] Song SQ, Rao RC, Yang HX, Liu HD, Zhang AM. Nanotechnology 2010;21:1–6. [8] Feng JT, Sui JH, Cai W, Wan JQ, Chakoli AN, Gao ZY. Mater Sci Eng B 2008;150: 208–12. [9] He Y, Huang L, Cai JS, Zheng XM, Sun SG. Electrochim Acta 2010;55:1140–4. [10] Dong Ck, Li X, Zhang Y, Qi JY, Yuan YF. Chem Rev 2009;25(6):936–40. [11] Morales-Cid G, Fekete A, Simonet BM, Lehmann R, Carhenas S, Zhang XM, et al. Anal Chem 2010;82:2743–52. [12] Lee PL, Chiu YK, Sun YC, Ling YC. Carbon 2010;48:1397–404. [13] Wan JQ, Cai W, Feng JT, Meng XX, Liu EZ. J Mater Chem 2007;17:1188–92. [14] Liu Y, Jiang W, Xu L, Yang XW, Li FS. Mater Lett 2009;63:2526–8. [15] Zhang Q, Zhu MF, Zhang QH, Li YG, Wang HZ. Compos Sci Technol 2009;69:633–8. [16] Tsukahara Y, Yamauchi T, Kawamoto T, Wada Y. Bull Chem Soc Jpn 2008;81(3): 387–92. [17] Chin SF, Iyer KS, Raston CL. Lab Chip 2008;8:439–42. [18] Lee J, Isobe T, Senna MJ. Colloid Interface Sci 1996;177:490. [19] Deng H, Li XL, Peng Q, Wang X, Chen JP, Li YD. Angew Chem Int Ed 2005;44: 2782–5. [20] Laurent S, Forge D, Port M, Roch A, Robic C, Elst LV, et al. Chem Rev 2008;108: 2064–110. [21] Jang J, Nah H, Lee JH, Moon SH, Kim MG, Cheon J. Angew Chem 2009;121:1260–4. [22] Wu HX, Liu G, Wang X, Zhang JM, Chen Y, Shi JL, et al. Acta Biomater 2011;7: 3496–504. [23] Wu HX, Liu G, Zhuang YM, Wu DM, Zhang HQ, Yang H, et al. Biomaterials 2011;32:4867–76.