Communication pubs.acs.org/IC
Graphitic Carbon Nanocubes Derived from ZIF‑8 for Photothermal Therapy Wei Chen,† Xiaoman Zhang,‡ Fujin Ai,‡ Xueqing Yang,† Guangyu Zhu,*,‡,§ and Feng Wang*,†,§ †
Department of Physics and Materials Science and ‡Department of Biology and Chemistry, City University of Hong Kong, 83 Tat Chee Avenue, Hong Kong SAR, China § City University of Hong Kong Shenzhen Research Institute, Shenzhen 518057, China S Supporting Information *
ABSTRACT: Graphitic carbon nanocubes (GCNCs) were prepared by pyrolysis of ZIF-8 nanocubes. The GCNCs resemble the structure of N-doped graphite and exhibit a high photothermal conversion efficiency of 40.4%. In vitro tests demonstrate that the GCNCs are highly biocompatible and induce an effective photothermal therapy effect under 808 nm irradiation. Our study provides a facile strategy for preparing functional carbon nanomaterials of prescribed size, morphology, and porous structure for bioapplications.
Figure 1. Schematic illustration of the GCNC synthesis.
nium bromide as a surfactant to control the particle morphology. Electron microscopy reveals a narrow size distribution of the assynthesized ZIF-8 nanocubes with an edge length of about 55 nm (Figure S1a,b). Powder X-ray diffraction (XRD) pattern shows a strong diffraction peak at a 2θ value of 7.2° (Figure S1c), which agrees with previous reports and confirms the formation of ZIF-8 crystals.9 After calcination at 800 °C for 1 h, the ZIF-8 nanocubes were converted into composite nanocubes mainly composed of carbon and zinc, with a largely preserved morphology and a slightly decreased size due to the degradation of organic linkers (Figure S1d,e). By removal of the zinc residuals through treatment with an HCl solution (4 M), the GCNCs were obtained and purified by deionized water for subsequent investigations. Parts a and b of Figure 2 show typical scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images of the as-synthesized GCNCs with a cubic morphology inherent from the parent ZIF-8. Compositional analysis of the nanocubes by energy-dispersive X-ray spectroscopy confirms the removal of most residual impurities (Figure S1f). The high-resolution TEM (HRTEM) image of a single GCNC shown in Figure 2c reveals an amorphous matrix of the nanocube with oriented multilayer domains (indicated by red arrows) on the edge. The XRD pattern of the GCNCs in Figure 2d exhibits a sharp peak at 23° corresponding to the (002) plane of graphite,10 which is superimposed on a large bump distributed in a wide range of diffraction angles. The result indicates an amorphous body of the GCNCs with partially ordered planes, which is in accordance with HRTEM analysis of the sample. N2 adsorption−desorption isotherms at 77 K (Figure 2e) determines a pore size of around 1.0 nm in the GCNCs, which is close to that in the ZIF-8.9 The structural information on the GCNCs was further examined by Raman and X-ray photoelectron (XPS) spectros-
ne central task in the field of hyperthermia therapy is developing suitable nanotransducers to maximize the therapeutic effect and to minimize the side effect due to absorption of the thermal energy by healthy cells. Magnetic nanoparticles such as Fe5C2, Fe3O4, and Fe@Fe3O4 nanoparticles were initially used to induce heating effects following exposure to alternating magnetic fields.1 Noble-metal nanoparticles2 and copper halogenides3 characterized with high extinction coefficients have also been widely used for hyperthermia therapy by photon excitations in a process known as photothermal therapy (PTT). Carbon-based nanomaterials4 represent another important and growing class of hyperthermic agents being developed for PTT. By comparison, these carbon nanomaterials are cost-effective and can be readily conjugated with a wide diversity of molecules and nanoparticles to achieve combinational therapies.5 In recent years, considerable efforts have been devoted to exploring new carbon nanomaterials, and porous carbon nanospheres have emerged as a new platform for PTT. It has been established that the porous structure provides an added flexibility of loading functional molecules and drugs in comparison with conventional carbon nanotubes and nanosheets (graphene).6 On a separate note, previous studies reveal that the effects of the pore size and particle morphology can also be exploited to optimize the therapeutic performance.7 Encouraged by these discoveries, here we developed a new class of graphitic nanocarbons that feature a cubic morphology comprising small pores by pyrolysis of a zeolitic imidazolate framework, ZIF-8.8 We also demonstrate efficient PTT of human cancer cells by using the ZIF-8-derived graphitic carbon nanocubes (GCNCs). Figure 1 depicts the synthetic procedures for preparing the GCNCs. The ZIF-8 precursor nanocubes were first synthesized according to a literature method9 by using cetyltrimethylammo-
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© XXXX American Chemical Society
Received: April 24, 2016
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DOI: 10.1021/acs.inorgchem.6b01013 Inorg. Chem. XXXX, XXX, XXX−XXX
Communication
Inorganic Chemistry
Figure 3. (a) Photographs of the GCNCs before (left) and after (right) surface coating with F127. The photographs were taken 10 min after preparation of the dispersions (10 μg mL−1). (b) UV−visible absorption spectrum of the GCNCs dispersed in water (10 μg mL−1). (c) Temperature of water solutions comprising various concentrations of GCNCs under irradiation of an 808 nm diode laser (9 W cm−2) for varying times (0−10 min). Error bars shown represent the standard deviations from three repeated measurements. (d) Photothermal stability of a GCNC colloid (1.0 mg mL−1) over 10 irradiation cycles. In each cycle, the 808 nm diode laser operating at 0.5 W was turned on for 3 min and then turned off for 3 min to cool the colloid. Figure 2. (a and b) SEM and TEM images of the as-synthesized GCNCs. (c) HRTEM image of a typical GCNC. (d) XRD pattern of the GCNCs. (e) N2 adsorption and desorption isotherms of the GCNCs at 77 K. Inset: pore-size distribution. (f) Raman spectrum of the GCNCs. (g) XPS spectrum of the GCNCs. (h and i) Gaussian deconvolutions of the C 1s and N 1s peaks shown in part g.
potential (−10 mV; Figure S2). The UV−visible absorption spectrum of the GCNCs in water dispersion reveals a continuous absorption band spanning from UV to the near-IR (NIR) spectral region (Figure 3b). Because biological tissues and water show minimal absorption in the NIR spectral region,14 an 808 nm diode laser was chosen as the light source in subsequent experiments in order to minimize the heating effect due to direct absorption of the irradiation energy. According to the absorption spectrum, the mass extinction coefficient of the GCNCs at 808 nm was determined to be 9.4 L g−1 cm−1. In order to evaluate the performance of the GCNCs in an aqueous media to induce a sufficiently high increase in temperature for PTT, we recorded the temperature elevation of aqueous dispersions containing different concentrations of GCNCs (5−100 μg mL−1) under irradiation of an 808 nm diode laser at a power density of 9 W cm−2 (Figure 3c). Prior to the addition of GCNCs, the temperature of pure water was only increased by 3.0 °C in 10 min. With the addition of GCNCs of increasing concentrations, a steadily enhanced temperature increase of the solvent was detected. According to Roper’s method,15 the photothermal conversion efficiency of the GCNCs was determined to be 40.4% (Figure S3). Notably, at a relatively low GCNC concentration of 20 μg mL−1, the temperature can be elevated above the photoablation limit of 50 °C (based on the Arrhenius damage integral16) within 8 min. Because of the high penetration depth of 808 nm light in biological tissues, a significant temperature elevation can also be induced when the laser irradiates the GCNC dispersion through pork tissues (Figure S4). In addition, the GCNCs display high photothermal stability. They largely preserve the ability to induce rapid temperature increases by repetitive 808 nm diode-laser irradiation (Figure 3d). In a further set of experiments, we assessed the biocompatibility and PTT effect of the GCNCs by in vitro incubation with HeLa cells. A standard 3-(4,5-dimethylthiazol-2-yl)-2,5-diphe-
copies. The Raman spectrum in Figure 2f shows both a disorderinduced D band at ∼1380 cm−1 and a graphite-related G band at ∼1600 cm−1, which is consistent with the HRTEM and XRD results. The presence of a G band, which is attributed to the vibration of sp2-hybridized carbon atoms,11 clearly demonstrates the development of well-defined graphitic domains in the samples. The XPS spectrum in Figure 2g exhibits the principal C 1s, N 1s, and O 1s core-level peaks. The spectrum was corrected by the Shirley algorithm method before curve deconvolution. The C 1s core-level peak can be resolved into four components centered at 284.8, 284.9, 288.0, and 285.8 eV (Figure 2h), which are attributed to C sp3−C sp3, C sp2−C sp2, CN, and C−N bonds, respectively.10,12 Similarly, the N 1s peak can also be resolved into three components centered at 398.0, 399.0, and 400.7 eV corresponding to pyridinic, pyrrolic, and quaternary nitrogen atoms, respectively (Figure 2i).11 In addition, the absorptions of C−N and CN were also observed in the Fourier transform infrared (FTIR) spectrum of the GCNCs at 1208 and 1600 cm−1, respectively (Figure S1g). Taken together, the results reveal a nitrogen-doped graphite structure of the sample. We next surface-modified the as-synthesized GCNCs by the nonionic surfactant F127, which is widely used to coat carbon nanomaterials because of its high biocompatibility and high value of the hydrophilic−lipophilic balance. F127 binds to the surface of GCNCs through hydrophobic interactions and imparts water dispersibility to the nanocubes (Figure 3a).13 The successful coating of the GCNCs with F127 is confirmed by the presence of C−H (2873 cm−1) and C−O−C (1115 and 843 cm−1) absorptions in the FTIR spectrum and by a negative surface ζ B
DOI: 10.1021/acs.inorgchem.6b01013 Inorg. Chem. XXXX, XXX, XXX−XXX
Inorganic Chemistry
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ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (Grants 21573185 and 21371145) and the Research Grants Council of Hong Kong (CityU Grant 11208215). We thank Haidong Bian for help with sample characterization.
nyltetrazolium bromide assay reveals no attenuation of the cell viabilities in the presence of the GCNCs at a concentration range of 12.5−100 μg mL−1 (Figure 4a), demonstrating good
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biocompatibility of the GCNCs. In stark contrast, a clear decrease in the cell viability was detected when NIR irradiation was added. Notably, almost all of the cells were killed at a GCNC concentration of 50 μg mL−1, implying a high photothermal efficacy. The heat-induced cell-killing effect was further confirmed by confocal fluorescence images of HeLa cells stained with calcein AM, a cell-permeant dye to determine the cell viability. Clearly, very few viable cells are left after treatment with GCNCs upon NIR irradiation (Figure 4b). By comparison, the cells remain viable after 808 nm irradiation in the absence of GCNCs (Figure 4b). These results clearly support the critical role of the GCNCs in killing human cancer cells through a PTT effect. In conclusion, we have originally fabricated a class of ZIF-8derived GCNCs displaying high biocompatibility and photothermal conversion efficiency. Despite preliminary in many aspects, this study represents an important advance in the development of new photothermal agents. When one considers the high flexibility in controlling the formation of MOF materials by adjusting the organic linkers and synthetic variables, our method can be readily adapted to prepare nanocarbons with size, morphology, and microstructure that are inaccessible to conventional polymerization or carbonization methods, thereby providing new platforms for downstream biomedical applications.
ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.6b01013. Experimental details and Figures S1−S4 (PDF)
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REFERENCES
(1) (a) Yu, J.; Ju, Y. M.; Zhao, L. Y.; Chu, X.; Yang, Y. L.; Tian, Y. L.; Sheng, F. G.; Lin, J.; Liu, F.; Dong, Y. H.; Hou, Y. L. ACS Nano 2016, 10, 159−169. (b) Yang, G. B.; Gong, H.; Liu, T.; Sun, X. Q.; Cheng, L.; Liu, Z. Biomaterials 2015, 60, 62−71. (c) Zhou, Z.; Sun, Y.; Shen, J.; Wei, J.; Yu, C.; Kong, B.; Liu, W.; Yang, H.; Yang, S.; Wang, W. Biomaterials 2014, 35, 7470−7478. (2) (a) Yang, J. P.; Shen, D. K.; Zhou, L.; Li, W.; Li, X. M.; Yao, C.; Wang, R.; El-Toni, A. M.; Zhang, F.; Zhao, D. Y. Chem. Mater. 2013, 25, 3030−3037. (b) Chen, C. W.; Lee, P. H.; Chan, Y. C.; Hsiao, M.; Chen, C. H.; Wu, C. P.; Wu, P. R.; Tsai, D. P.; Tu, D. T.; Chen, X. Y.; Liu, R. S. J. Mater. Chem. B 2015, 3, 8293−8302. (c) Pacardo, D. B.; Neupane, B.; Rikard, S. M.; Lu, Y.; Mo, R.; Mishra, S. R.; Tracy, J.; Wang, G. F.; Ligler, F. S.; Gu, Z. Nanoscale 2015, 7, 12096−12103. (3) Tian, Q. W.; Jiang, F. R.; Zou, R. R. J.; Liu, Q.; Chen, Z. G.; Zhu, M. F.; Yang, S. P.; Wang, J. L.; Wang, J. H.; Hu, J. Q. ACS Nano 2011, 5, 9761−9771. (4) (a) Zhou, J.; Lu, Z. G.; Wang, X. J.; Liao, Y.; Ma, Z. F.; Li, F. Y.; Zhu, X. J. Biomaterials 2013, 34, 9584−9592. (b) Cheng, L.; Yang, K.; Chen, Q.; Liu, Z. ACS Nano 2012, 6, 5605−5613. (5) Zhu, Y. W.; Murali, S.; Cai, W. W.; Li, X. S.; Suk, J. W.; Potts, J. R.; Ruoff, R. S. Adv. Mater. 2010, 22, 3906−3924. (6) Khan, S. A.; Kanchanapally, R.; Fan, Z.; Beqa, L.; Singh, A. K.; Senapati, D.; Ray, P. C. Chem. Commun. 2012, 48, 6711−6713. (7) (a) Vallet-Regí, M.; Balas, F.; Arcos, D. Angew. Chem., Int. Ed. 2007, 46, 7548−7558. (b) Huang, X.; Teng, X.; Chen, D.; Tang, F.; He. Biomaterials 2010, 31, 438−448. (8) (a) Tang, J.; Salunkhe, R. R.; Liu, J.; Torad, N. L.; Imura, M.; Furukawa, S.; Yamauchi, Y. J. Am. Chem. Soc. 2015, 137, 1572−1580. (b) Torad, N. L.; Hu, M.; Kamachi, Y.; Takai, K.; Imura, M.; Naito, M.; Yamauchi, Y. Chem. Commun. 2013, 49, 2521−2523. (c) Torad, N. L.; Li, Y.; Ishihara, S.; Ariga, K.; Kamachi, Y.; Lian, H. Y.; Hamoudi, H.; Sakka, Y.; Chaikittisilp, W.; Wu, K. C.; Yamauchi, Y. Chem. Lett. 2014, 43, 717−719. (9) Pan, Y.; Heryadi, D.; Zhou, F.; Zhao, L.; Lestari, G.; Su, H.; Lai, Z. CrystEngComm 2011, 13, 6937−6940. (10) (a) Park, K. S.; Ni, Z.; Cote, A. P.; Choi, J. Y.; Huang, R.; UribeRomo, F. J.; Chae, H. K.; O'Keeffe, M.; Yaghi, O. M. Proc. Natl. Acad. Sci. U. S. A. 2006, 103, 10186−10191. (b) Zheng, F.; Yang, Y.; Chen, Q. Nat. Commun. 2014, 5. (11) Reddy, A.; Srivastava, A.; Gowda, S.; Gullapalli, H.; Dubey, M.; Ajayan, P. ACS Nano 2010, 4, 6337. (12) Panchapakesan, B.; Lu, S.; Sivakumar, K.; Teker, K.; Cesarone, G.; Wickstrom, E. NanoBiotechnology 2005, 1, 133−139. (13) (a) Lin, Y.; Alexandridis, P. J. Phys. Chem. B 2002, 106, 10834− 10844. (b) Granite, M.; Radulescu, A.; Cohen, Y. Langmuir 2012, 28, 11025−11031. (14) Ai, F.; Ju, Q.; Zhang, X.; Chen, X.; Wang, F.; Zhu, G. Sci. Rep. 2015, 5, 10785. (15) Roper, D.; Ahn, W.; Hoepfner, M. J. Phys. Chem. C 2007, 111, 3636−3641. (16) Splinter, R.; Hooper, B. An Introduction to Biomedical Optics; Taylor & Francis: New York, 2007; pp 220−233.
Figure 4. (a) Viabilities of HeLa cells cocultured with different concentrations of GCNCs for 48 h. (b) Optical micrographs of HeLa cells in the presence (100 μg mL−1) and absence of GCNCs. NIR irradiation was provided by an 808 nm diode laser at a power density of 9 W cm−2 for 3 min.
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DOI: 10.1021/acs.inorgchem.6b01013 Inorg. Chem. XXXX, XXX, XXX−XXX
