DOI: 10.1002/chem.201402982
Communication
& Fluorescent Probes
From Metal–Organic Framework to Intrinsically Fluorescent Carbon Nanodots Arlin Jose Amali, Hideto Hoshino, Chun Wu, Masanori Ando, and Qiang Xu*[a] tion. Simple carbonization of the assembled MOF particles at high temperatures affords a three-dimensional hierarchically porous carbon framework with both micro- and mesopores.[14e] Herein, we present for the first time a facile methodology to use MOF nanoparticles (NPs) as a precursor to prepare carbon nanodots with intrinsic fluorescence, which exhibit excellent performance for biosafe patterning (Scheme 1).
Abstract: Highly photoluminescent carbon nanodots (CNDs) were synthesized for the first time from metal–organic framework (MOF, ZIF-8) nanoparticles. Coupled with fluorescence and non-toxic characteristics, these carbon nanodots could potentially be used in biosafe color patterning.
Light-emitting quantum-sized carbon nanodots (CNDs) have attracted tremendous attention because of numerous possible applications in drug/gene delivery, bioimaging, photocatalysis, energy conversion, optoelectronics, sensing, and other directions.[1] CNDs exhibit several promising advantages, such as excellent chemical stability, up-conversion emission, easy functionalization, pH-sensitivity, and resistance to photobleaching compared with semiconductor quantum dots and rare-earth and organic fluorescent materials.[2] To date, considerable approaches, such as arc-discharge,[3] laser-ablation,[4] electrochemical synthesis,[5] microwave synthesis,[6] and combustion/thermal[7] routes have been used to synthesize CNDs, of which the thermal route was regarded as a direct and efficient way.[8] However, the performance of CND-based solid-state luminescent devices reported to date is still not satisfactory, because strong fluorescence quenching occurs in dry and aggregate states.[9] More importantly, although CNDs have been demonstrated as probes in cellular imaging, clear evidence to ensure their biosafety is highly desired, which can be achieved, as shown in this work, by comparing CNDs with existing cell imaging probes. Recently, it has been demonstrated that metal–organic frameworks (MOFs),[10–12] also called as porous coordination polymers (PCPs), can be used as templates/precursors to prepare porous carbons through thermal conversion.[13–16] The MOF-derived nanoporous carbons exhibit high specific surface areas and hydrogen uptakes, as well as excellent electrochemical properties as electrode materials for electrochemical double-layered capacitors.[13–16] Very recently, meso-/macropores have been induced as additional second-order structures by the assembly of MOF particles prepared with ultrasonica-
Scheme 1. Schematic illustration for the formation of carbon nanodots (CNDs) derived from ZIF-8 NPs and their aqueous dispersion under visible and UV lights.
Herein, for preparation of the fluorescent CNDs, we used the NPs of the zeolitic imidazolate framework, ZIF-8 [Zn(MeIM)2 ; MeIM = 2-methylimidazole],[17] which were prepared by using a sonochemical approach according to our recent report, as the precursor. [14e] Briefly, by mixing the methanolic solutions of precursors, zinc nitrate and MeIM, as well as triethylamine, under ultrasonication immediately resulted in the formation of ZIF-8 NPs as a white solid. The powder X-ray diffraction (PXRD) pattern of ZIF-8 NPs confirmed the preserved ZIF-8 framework, and the transmission electron microscopic (TEM) and highangle annular dark-field scanning transmission electron microscopic (HAADF-STEM) studies displayed the morphology of resultant ZIF-8 particles with a size of 20–100 nm.[14e] In contrast to the formation of porous carbons by carbonization at high temperatures,[14e, 18] carbon nanodots (CNDs) were, surprisingly, obtained by carbonizing ZIF-8 NPs at a lower tem-
[a] Dr. A. J. Amali, Dr. H. Hoshino, Dr. C. Wu, Dr. M. Ando, Prof. Q. Xu National Institute of Advanced Industrial Science and Technology (AIST), Ikeda, Osaka 563-8577 (Japan) Fax: (+ 81) 72-751-9629 E-mail: [email protected] Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201402982. Chem. Eur. J. 2014, 20, 1 – 5
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Communication perature, 500 8C. By carbonizing ZIF-8 NPs at 500 8C in an argon flow for 10 h, carbon nanodots (CNDs) were formed along with ZnO, showing characteristic peaks in the PXRD spectrum (Figure 1 a), which can be removed by washing with aqueous HCl solution (5 vol %; Figure 1 b). A broad peak can be observed at around 2q = 258 for CNDs, corresponding to
can be obtained from the ZIF-8 NPs prepared with ultrasonication, but cannot be produced by using bulk ZIF-8 crystals prepared without ultrasonication, under the same condition (Figure S4 in the Supporting Information). X-ray photoelectron spectroscopic (XPS) measurements were carried out to probe the composition of the CNDs, which clearly revealed the presence of nitrogen and oxygen in the CNDs. The C 1 s spectrum (Figure S5a in the Supporting Information) shows three peaks at 284.6, 286.6, and 288.1 eV, which are attributed to C C, C O, and C=N/C=O, respectively.[19] The N 1 s spectrum (Figure S5b in the Supporting Information) shows two peaks at 397.5 and 399.5 eV, which can be attributed to N=C, and N H, respectively.[20] The O 1 s spectrum (Figure S5c in the Supporting Information) exhibits two peaks at 531.7 and 533.0 eV, which are assignable to C=O and C OH/C-O-C groups, respectively.[21] The presence of these functional groups imparts excellent solubility to the CNDs in water without further chemical modification, which is essential for biologically motivated works, and simultaneously gives a convenient handle for subsequent surface functionalization, which can be realized easily by using well-established conjugation protocols.[22] To better understand the characteristics of CNDs, photophysical studies were performed. The dilute aqueous solution of CNDs (1 mg mL 1) showed a broad absorption spectrum (Figure 2 a) with peaks centered at 210 and 335 nm, and a hump around 370 nm, which represent the typical absorptions of an aromatic p system with extended conjugation in the CND structure. Further, the high energy tail in the visible region is attributed to Mie scattering caused by nanosized particles.[23] In the fluorescence spectrum (Figure 2 b), the CNDs showed emission maximum 412 nm when excited at 330 nm, and show a bright blue color under UV irradiation (385 nm) (Scheme 1). Excitation-independent photoluminescent behav-
Figure 1. PXRD profiles of ZIF-8 NP-derived CNDs a) before and b) after washing with aqueous HCl solution (5 vol %) and c) TEM and d) HAADFSTEM images of CNDs.
a typical (002) interlayer pack of graphite-type carbon, after washing with aqueous HCl solution followed by purification by using membrane dialysis (molecular weight cutoff 14 kDa). TEM and HAADFSTEM images displayed a uniform dispersion of CNDs with a mean particle diameter of 2.2 nm without apparent aggregation in water (Figure 2 c, d). HAADFSTEM and EDS analyses of randomly selected positions of CNDs display uniform compositions (Figure S1 in the Supporting Information). It should be noted that the carbonization temperature is a crucial factor for getting CNDs from ZIF-8 NPs. During carbonization, the zinc ions, the inorganic part of ZIF-8, turn to ZnO and the organic ligand MeIM becomes the carbon nanodots (Figure S2 in the Supporting Information). When the carbonization temperature was below 500 8C, the CND yield was very low, which can be attributed to the high thermal stability of ZIF-8 framework. On the other hand, if the carbonization temperature was above 600 8C, porous carbons were formed as in the previous works (Figure S3 in the Supporting Information).[14] The morphology of ZIF-8 is another crucial factor for getting CNDs. The CNDs &
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Figure 2. a) UV/Vis absorption spectrum; b) emission spectrum (lex = 330 nm) of an aqueous solution of CNDs; c) emission spectra of CNDs recorded for progressively longer excitation wavelength of 20 nm increments; and d) time-resolved fluorescence-decay curve of CNDs (lex = 375 nm) measured at 410 nm.
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Communication ior, which is rare in fluorescent carbon materials, was observed.[24] The maximum emission wavelength at different excitation wavelengths (Figure 2 c) remained at 412 nm, which can avoid autofluorescence during their applications.[25] The highest fluorescent intensity was observed at lex = 340 and 360 nm. The observed excitation-independent emission over the excitation wavelength range of 300–400 nm indicates a high degree of homogeneity with relatively uniform and well-passivated CND surface.[26] The CNDs can freely disperse in water without ultrasonication, looking transparent at low concentrations, and thus they can be called “water-soluble CNDs” (Scheme 1). The CNDs solution is very stable, and there was no nanoparticle precipitation in six months. Even at a very dilute concentration, the CND solution can emit bright blue light when it is irradiated by using a UV lamp (385 nm). This bright blue fluorescence of CNDs can be easily seen by naked eyes (Scheme 1). The fluorescence lifetime of CNDs was assessed by time-correlated single-photon counting (TCSPC) measurements. The lifetime data of these CNDs were very well fitted to a bi-exponential function (Figure 2 d). The observed lifetimes of the CNDs are 1.60 and 3.12 ns. The lifetime of CNDs in nanoseconds suggests that the synthesized CNDs are most suitable for optoelectronic and biological applications.[27] Usually, fluorescence is strongly quenched when the aqueous solutions of CNDs are deposited on solid substrates owing to the formation of aggregates.[9] However, the MOF-derived CNDs showed, interestingly, unaltered fluorescent emissions when deposited on paper. The paper was coated with an aqueous solution of CNDs and then dried in air. After drying, the paper was colorless as plain paper in normal daylight (Figure 3 a), and fluorescent as blue under a UV irradiation (385 nm; Figure 3 b). It should be noted that CNDs with a concentration as low as 1 10 6 mg mL 1 can give a fluorescence strong enough to be detected by naked eyes. Thus, we can apply these CNDs as fluorescent carbon inks for fluorescent patterning. Moreover, the prepared fluorescent pattern remains unchanged after six months in an indoor environment, exhibiting high potential for practical applications. It is reported that the water-soluble fluorescent CNDs are an ideal cell-imaging probe with minimum cytotoxicity.[28] However, functionalization is an important step for cellular and subcellular targeting.[29] Interestingly, we found our CNDs could be
very safe to the healthy cells and could only enter into weak/ dead cells without any further functionalization (Figure 3 c–e). The human cell line GM0637 was used, and the cells were transfected with a mammalian expression plasmid encoding H2 AX-eBAF-Y containing EYFP,[30] and were exposed in CNDadded medium for one hour. The GM0637 cell images were obtained under UV excitation (lex = 377 nm) for CNDs and blue excitations for EYFP (lex = 473 nm), and bright field (BF; Figure 3 c–e). By comparing the three images, we can easily understand that the EYFP positive cells are CND negative and vice versa. H2 AX-eBAF-Y is distributed in cellular nucleus, because the histone H2 AX is a member of core histone and contributes to nucleosome (i.e., a basic unit of DNA packaging in eukaryotes) formation. The expression plasmid also carries the antibiotic resistant gene, and thus EYFP positive cells are healthier, but the weaker or negative cells are also morphologically damaged by G418 exposure (BF). The fluorescent signals were only observed from the damaged and unhealthy cell after CND exposure. This result clearly evidences that the CNDs cannot be incorporated into normal cells, which are thus very safe to be used in various applications in day-to-day life. In summary, for the first time, we have utilized the metal–organic framework nanoparticles as a precursor to prepare water-soluble carbon nanodots (CNDs). Simple carbonization of the ZIF-8 NPs, prepared with ultrasonication, at a mild temperature (500 8C) gave carbon nanodots with strong and stable luminescence, of which the maximum emission wavelength is independent on the excitation wavelength in the range of 300-400 nm. The retention of fluorescence in the solid state and the ability to distinguish the weaker cells from the healthier cells open up avenues to applications of these MOF-derived CNDs in the field of biosafe fluorescent patterning.
Experimental Section Preparation of ZIF-8 NPs In a typical synthesis, zinc nitrate (Zn(NO3)2·6 H2O, 25 mmol, 7.435 g) was dissolved in methanol (500 mL). 2-Methylimidazole (MeIM, 25 mmol, 2.052 g) and triethylamine (TEA, 36 mmol, 3.267 g) were dissolved in methanol (500 mL) at RT (25 8C). These solutions were mixed while sonicating in a bath sonicator for 2 min and kept as such. The solution became turbid immediately. After 4 h, the turbid solution was centrifuged, washed five times with methanol, and dried at 80 8C for 4 h to get nanoparticles of ZIF-8.
Preparation of ZIF-8 NP-derived carbon nanodots (CNDs) The ZIF-8 NPs (0.25 g) were transferred into a ceramic boat and placed into a temperature-programmed furnace under an argon flow, heated from RT to 500 8C in 1 h, and then kept at 500 8C for 10 h and cooled to RT. The obtained material was added to HCl solution (200 mL, 5 vol % in water) to dissolve the ZnO formed along with carbon nanodots from ZIF-8 NPs. Thus prepared ZIF-8-derived carbon nanodots (CNDs) were purified by membrane dialysis (molecular weight cut off 14 kDa) against ultrapure water for two days. The outside water was changed every 6 h, and the obtained ZIF-8 NP-derived carbon nanodots, CNDs, were stored at RT for further studies.
Figure 3. CND-marked AIST logo on ordinary paper under a) daylight and b) UV light (lex = 385 nm), the H2 AX-eBAF-Y cell images showing the fluorescence from c) CNDs (lex = 377 nm); d) EYFP (lex = 473 nm), and e) the brightfield image. Chem. Eur. J. 2014, 20, 1 – 5
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[13] a) H.-L. Jiang, Q. Xu, Chem. Commun. 2011, 47, 3351; b) S.-L. Li, Q. Xu, Energy Environ. Sci. 2013, 6, 1656; c) J.-K. Sun, Q. Xu, Energy Environ. Sci. DOI: 10.1039/c4ee00517a. [14] a) B. Liu, H. Shioyama, T. Akita, Q. Xu, J. Am. Chem. Soc. 2008, 130, 5390; b) D. S. Yuan, J. X. Chen, S. X. Tan, N. N. Xia, Y. L. Liu, Electrochem. Commun. 2009, 11, 1191; c) B. Liu, H. Shioyama, H.-L. Jiang, X. Zhang, Q. Xu, Carbon 2010, 48, 456; d) J. Hu, L. Wang, Q. M. Gao, H. L. Guo, Carbon 2010, 48, 3599; e) A. J. Amali, J.-K. Sun, Q. Xu, Chem. Commun. 2014, 50, 1519. [15] a) M. Hu, J. Reboul, S. Furukawa, L. Radhakrishnan, Y. Zhang, P. Srinivasu, H. Iwai, H. Wang, Y. Nemoto, N. Suzuki, S. Kitagawa, Y. Yamauchi, Chem. Commun. 2011, 47, 8124; b) L. Radhakrishnan, J. Reboul, S. Furukawa, P. Srinivasu, S. Kitagawa, Y. Yamauchi, Chem. Mater. 2011, 23, 1225; c) S. Ma, G. A. Goenaga, A. V. Call, D.-J. Liu, Chem. Eur. J. 2011, 17, 2063; d) P. Pachfule, B. P. Biswal, R. Banerjee, Chem. Eur. J. 2012, 18, 11399; e) M. Hu, J. Reboul, S. Furukawa, N. L. Torad, Q. Ji, P. Srinivasu, K. Ariga, S. Kitagawa, Y. Yamauchi, J. Am. Chem. Soc. 2012, 134, 2864; f) S. J. Yang, T. Kim, J. H. Im, Y. S. Kim, K. Lee, H. Jung, C. R. Park, Chem. Mater. 2012, 24, 464; g) S. Lim, K. Suh, Y. Kim, M. Yoon, H. Park, D. N. Dybtsev, K. Kim, Chem. Commun. 2012, 48, 7447; h) S. J. Yang, C. R. Park, Adv. Mater. 2012, 24, 4010. [16] a) H.-L. Jiang, B. Liu, Y.-Q. Lan, K. Kuratani, T. Akita, H. Shioyama, F. Zong, Q. Xu, J. Am. Chem. Soc. 2011, 133, 11854; b) W. Chaikittisilp, M. Hu, H. Wang, H.-S. Huang, T. Fujita, K. C.-W. Wu, L.-C. Chen, Y. Yamauchi, K. Ariga, Chem. Commun. 2012, 48, 7259; c) A. Almasoudi, R. Mokaya, J. Mater. Chem. 2012, 22, 146; d) N. L. Torad, M. Hu, Y. Kamachi, K. Takai, M. Imura, M. Naitoa, Y. Yamauchi, Chem. Commun. 2013, 49, 2521. [17] a) K. S. Park, Z. Ni, A. P. Ct, J. Y. Choi, R. Huang, F. J. Uribe-Romo, H. K. Chae, M. Keeffe, O. M. Yaghi, Proc. Natl. Acad. Sci. USA 2006, 103, 10186; b) X. C. Huang, Y. Y. Lin, J. P. Zhang, X. M. Chen, Angew. Chem. 2006, 118, 1587; Angew. Chem. Int. Ed. 2006, 45, 1557. [18] See the Supporting Information. [19] S. Liu, J. Tian, L. Wang, Y. Luo, W. Lu, X. Sun, Biosens. Bioelectron. 2011, 26, 4491. [20] S. Fleutot, J.-C. Dupin, G. Renaudin, H. Martinez, Phys. Chem. Chem. Phys. 2011, 13, 17564. [21] M. Sevilla, A. B. Fuertes, Chem. Eur. J. 2009, 15, 4195. [22] S. N. Baker, G. A. Baker, Angew. Chem. 2010, 122, 6876; Angew. Chem. Int. Ed. 2010, 49, 6726. [23] a) G. S. He, L. X. Yuan, J. D. Bhawalka, P. N. Prasad, Appl. Opt. 1997, 36, 3387; b) G. S. He, J. Swiatkiewicz, Y. Jiang, P. N. Prasad, B. A. Reinhardt, L. S. Tan, R. Kannan, J. Phys. Chem. A 2000, 104, 4805; c) G. S. He, Q. D. Zheng, C. G. Lu, P. N. Prasad, IEEE. J. Quantum. Electron. 2005, 41, 1037; d) Q. D. Zheng, S. K. Gupta, G. S. He, L. S. Tan, P. N. Prasad, Adv. Funct. Mater. 2008, 18, 2770; e) G. S. He, K. T. Yong, J. Zhu, H. Y. Qin, P. N. Prasad, IEEE. J. Quantum. Electron. 2010, 46, 931. [24] a) R. Liu, D. Wu, S. Liu, K. Koynov, W. Knoll, Q. Li, Angew. Chem. 2009, 121, 4668; Angew. Chem. Int. Ed. 2009, 48, 4598; b) D. Pan, J. Zhang, Z. Li, C. Wu, X. Yan, M. Wu, Chem. Commun. 2010, 46, 3681; c) M. J. Krysmann, A. Kelarakis, P. Dallas, E. P. Giannelis, J. Am. Chem. Soc. 2012, 134, 747; d) X. Zhai, P. Zhang, C. Liu, T. Bai, W. Li, L. Dai, W. Liu, Chem. Commun. 2012, 48, 7955. [25] Y. Guo, Z. Wang, H. Shao, X. Jiang, Carbon 2013, 52, 583. [26] J. C. Vinci, I. M. Ferrer, S. J. Seedhouse, A. K. Bourdon, J. M. Reynard, B. A. Foster, F. V. Bright, L. A. Coln, J. Phys. Chem. Lett. 2013, 4, 239. [27] J. Peng, W. Gao, B. K. Gupta, Z. Liu, R. R. Aburto, L. Ge, L. Song, L. B. Alemany, X. Zhan, G. Gao, S. A. Vithayathil, B. A. Kaipparettu, A. A. Marti, T. Hayashi, J.-J. Zhu, P. M. Ajayan, Nano Lett. 2012, 12, 844. [28] S. J. Yu, M. W. Kang, H. C. Chang, K. M. Chen, Y. C. Yu, J. Am. Chem. Soc. 2005, 127, 17604. [29] Y. P. Sun, B. Zhou, Y. Lin, W. Wang, K. A. S. Fernando, P. Pathak, M. J. Meziani, B. A. Harruff, X. Wang, H. F. Wang, P. J. G. Luo, H. Yang, M. E. Kose, B. L. Chen, L. M. Veca, S. Y. Xie, J. Am. Chem. Soc. 2006, 128, 7756. [30] H. Hoshino, Y. Nakajima, Y. Ohmiya, Nat. Methods 2007, 4, 637.
Human cell line GM0637 was maintained in 10 % fetal bovine serum (FBS) supplemented DMEM at 37 8C, and seeded in six-well dishes 24 h before transfection. The cells were transfected with a mammalian expression plasmid encoding H2 AX-eBAF-Y, by using Lipofectamin 2000 (INVITROGEN).[30] After 9 h, the cells were reseeded onto a 35 mm glass-based dish (27 mm F, IWAKI) and cultured in 10 % FBS DMEM containing 500 mg mL 1 G418. After further incubation for 24 h, the carbon nanodots (CNDs) were added into the medium to final concentration of 5 mg mL 1, and the cells were exposed to the CNDs for 1 h. Then the cells were washed twice with fresh medium and replaced with phenol red free 10 % FBS DMEM. Fluorescence images of live cells were acquired with a Biorevo (BZ-9000; KEYENCE) equipped with a 40 1.0 NA objective (Nikon).
Acknowledgements The authors acknowledge Dr. T. Uchida for TEM measurements and AIST for financial support. A.J.A. thanks AIST for a postdoctoral fellowship. Keywords: carbon · fluorescent probes · metal–organic frameworks · nanodots · quantum dots [1] a) H. Li, Z. Kang, Y. Liu, S.-T. Lee, J. Mater. Chem. 2012, 22, 24230; b) L. C. Cheng, X. M. Jiang, J. Wang, C. Y. Chen, R. S. Liu, Nanoscale 2013, 5, 3547. [2] S. Zhu, S. Tang, J. Zhang, B. Yang, Chem. Commun. 2012, 48, 4527. [3] X. Xu, R. Ray, Y. Gu, H. J. Ploehn, L. Gearheart, K. Raker, W. A. Scrivens, J. Am. Chem. Soc. 2004, 126, 12736. [4] S.-L. Hu, K.-Y. Niu, J. Sun, J. Yang, N.-Q. Zhao, X.-W. Du, J. Mater. Chem. 2009, 19, 484. [5] a) J. Zhou, C. Booker, R. Li, X. Zhou, T.-K. Sham, X. Sun, Z. Ding, J. Am. Chem. Soc. 2007, 129, 744; b) L. Zheng, Y. Chi, Y. Dong, J. Lin, B. Wang, J. Am. Chem. Soc. 2009, 131, 4564. [6] a) H. Zhu, X. Wang, Y. Li, Z. Wang, F. Yang, X. Yang, Chem. Commun. 2009, 5118; b) A. Jaiswal, S. S. Ghosh, A. Chattopadhyay, Chem. Commun. 2012, 48, 407. [7] a) H. Liu, T. Ye, C. Mao, Angew. Chem. 2007, 119, 6593; Angew. Chem. Int. Ed. 2007, 46, 6473; b) Y. Yang, J. Cui, M. Zheng, C. Hu, S. Tan, Y. Xiao, Q. Yang, Y. Liu, Chem. Commun. 2012, 48, 380; c) C. Zhu, J. Zhai, S. Dong, Chem. Commun. 2012, 48, 9367. [8] a) D. Pan, J. Zhang, Z. Li, M. Wu, Adv. Mater. 2010, 22, 734; b) Y. Dong, R. Wang, H. Li, J. Shao, Y. Chi, X. Lin, G. Chen, Carbon 2012, 50, 2810. [9] S. Qu, X. Wang, Q. Lu, X. Liu, L. Wang, Angew. Chem. 2012, 124, 12381; Angew. Chem. Int. Ed. 2012, 51, 12215. [10] a) M. Eddaoudi, J. Kim, N. Rosi, D. Vodak, J. Wachter, M. Keeffe, O. M. Yaghi, Science 2002, 295, 469; b) J.-P. Zhang, X.-C. Huang, X.-M. Chen, Chem. Soc. Rev. 2009, 38, 2385; c) G. Frey, C. Serre, Chem. Soc. Rev. 2009, 38, 1380; d) D. Yuan, D. Zhao, D. Sun, H.-C. Zhou, Angew. Chem. 2010, 122, 5485; Angew. Chem. Int. Ed. 2010, 49, 5357; e) B. Chen, S. Xiang, G. Qian, Acc. Chem. Res. 2010, 43, 1115; f) T. Wu, L. Wang, X. Bu, V. Chau, P. Feng, J. Am. Chem. Soc. 2012, 134, 4517. [11] a) S. K. Ghosh, S. Bureekaew, S. Kitagawa, Angew. Chem. 2008, 120, 3451; Angew. Chem. Int. Ed. 2008, 47, 3403; b) L. Ma, A. Jin, Z. Xie, W. Lin, Angew. Chem. 2009, 121, 10089; Angew. Chem. Int. Ed. 2009, 48, 9905; c) J. Lee, O. K. Farha, J. Roberts, K. A. Scheidt, S. T. Nguyen, J. T. Hupp, Chem. Soc. Rev. 2009, 38, 1450; d) S. Motoyama, R. Makiura, O. Sakata, H. Kitagawa, J. Am. Chem. Soc. 2011, 133, 5640; e) M. M. Wanderley, C. Wang, C.-D. Wu, W. Lin, J. Am. Chem. Soc. 2012, 134, 9050. [12] a) J. S. Seo, D. Whang, H. Lee, S. I. Jun, J. Oh, Y. J. Jeon, K. Kim, Nature 2000, 404, 982; b) S. Kitagawa, R. Kitaura, S. Noro, Angew. Chem. 2004, 116, 2388; Angew. Chem. Int. Ed. 2004, 43, 2334.
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COMMUNICATION & Fluorescent Probes
Highly photoluminescent carbon nanodots (CNDs) were synthesized for the first time from metal–organic framework (ZIF-8) nanoparticles. Coupled with fluorescence and non-toxic characteristics, these carbon nanodots could potentially be used in biosafe color patterning (see figure).
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A. J. Amali, H. Hoshino, C. Wu, M. Ando, Q. Xu* && – && From Metal–Organic Framework to Intrinsically Fluorescent Carbon Nanodots
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& Fluorescent Probes
From Metal–Organic Framework to Intrinsically Fluorescent Carbon Nanodots Arlin Jose Amali, Hideto Hoshino, Chun Wu, Masanori Ando, and Qiang Xu*[a] tion. Simple carbonization of the assembled MOF particles at high temperatures affords a three-dimensional hierarchically porous carbon framework with both micro- and mesopores.[14e] Herein, we present for the first time a facile methodology to use MOF nanoparticles (NPs) as a precursor to prepare carbon nanodots with intrinsic fluorescence, which exhibit excellent performance for biosafe patterning (Scheme 1).
Abstract: Highly photoluminescent carbon nanodots (CNDs) were synthesized for the first time from metal–organic framework (MOF, ZIF-8) nanoparticles. Coupled with fluorescence and non-toxic characteristics, these carbon nanodots could potentially be used in biosafe color patterning.
Light-emitting quantum-sized carbon nanodots (CNDs) have attracted tremendous attention because of numerous possible applications in drug/gene delivery, bioimaging, photocatalysis, energy conversion, optoelectronics, sensing, and other directions.[1] CNDs exhibit several promising advantages, such as excellent chemical stability, up-conversion emission, easy functionalization, pH-sensitivity, and resistance to photobleaching compared with semiconductor quantum dots and rare-earth and organic fluorescent materials.[2] To date, considerable approaches, such as arc-discharge,[3] laser-ablation,[4] electrochemical synthesis,[5] microwave synthesis,[6] and combustion/thermal[7] routes have been used to synthesize CNDs, of which the thermal route was regarded as a direct and efficient way.[8] However, the performance of CND-based solid-state luminescent devices reported to date is still not satisfactory, because strong fluorescence quenching occurs in dry and aggregate states.[9] More importantly, although CNDs have been demonstrated as probes in cellular imaging, clear evidence to ensure their biosafety is highly desired, which can be achieved, as shown in this work, by comparing CNDs with existing cell imaging probes. Recently, it has been demonstrated that metal–organic frameworks (MOFs),[10–12] also called as porous coordination polymers (PCPs), can be used as templates/precursors to prepare porous carbons through thermal conversion.[13–16] The MOF-derived nanoporous carbons exhibit high specific surface areas and hydrogen uptakes, as well as excellent electrochemical properties as electrode materials for electrochemical double-layered capacitors.[13–16] Very recently, meso-/macropores have been induced as additional second-order structures by the assembly of MOF particles prepared with ultrasonica-
Scheme 1. Schematic illustration for the formation of carbon nanodots (CNDs) derived from ZIF-8 NPs and their aqueous dispersion under visible and UV lights.
Herein, for preparation of the fluorescent CNDs, we used the NPs of the zeolitic imidazolate framework, ZIF-8 [Zn(MeIM)2 ; MeIM = 2-methylimidazole],[17] which were prepared by using a sonochemical approach according to our recent report, as the precursor. [14e] Briefly, by mixing the methanolic solutions of precursors, zinc nitrate and MeIM, as well as triethylamine, under ultrasonication immediately resulted in the formation of ZIF-8 NPs as a white solid. The powder X-ray diffraction (PXRD) pattern of ZIF-8 NPs confirmed the preserved ZIF-8 framework, and the transmission electron microscopic (TEM) and highangle annular dark-field scanning transmission electron microscopic (HAADF-STEM) studies displayed the morphology of resultant ZIF-8 particles with a size of 20–100 nm.[14e] In contrast to the formation of porous carbons by carbonization at high temperatures,[14e, 18] carbon nanodots (CNDs) were, surprisingly, obtained by carbonizing ZIF-8 NPs at a lower tem-
[a] Dr. A. J. Amali, Dr. H. Hoshino, Dr. C. Wu, Dr. M. Ando, Prof. Q. Xu National Institute of Advanced Industrial Science and Technology (AIST), Ikeda, Osaka 563-8577 (Japan) Fax: (+ 81) 72-751-9629 E-mail: [email protected] Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201402982. Chem. Eur. J. 2014, 20, 1 – 5
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Communication perature, 500 8C. By carbonizing ZIF-8 NPs at 500 8C in an argon flow for 10 h, carbon nanodots (CNDs) were formed along with ZnO, showing characteristic peaks in the PXRD spectrum (Figure 1 a), which can be removed by washing with aqueous HCl solution (5 vol %; Figure 1 b). A broad peak can be observed at around 2q = 258 for CNDs, corresponding to
can be obtained from the ZIF-8 NPs prepared with ultrasonication, but cannot be produced by using bulk ZIF-8 crystals prepared without ultrasonication, under the same condition (Figure S4 in the Supporting Information). X-ray photoelectron spectroscopic (XPS) measurements were carried out to probe the composition of the CNDs, which clearly revealed the presence of nitrogen and oxygen in the CNDs. The C 1 s spectrum (Figure S5a in the Supporting Information) shows three peaks at 284.6, 286.6, and 288.1 eV, which are attributed to C C, C O, and C=N/C=O, respectively.[19] The N 1 s spectrum (Figure S5b in the Supporting Information) shows two peaks at 397.5 and 399.5 eV, which can be attributed to N=C, and N H, respectively.[20] The O 1 s spectrum (Figure S5c in the Supporting Information) exhibits two peaks at 531.7 and 533.0 eV, which are assignable to C=O and C OH/C-O-C groups, respectively.[21] The presence of these functional groups imparts excellent solubility to the CNDs in water without further chemical modification, which is essential for biologically motivated works, and simultaneously gives a convenient handle for subsequent surface functionalization, which can be realized easily by using well-established conjugation protocols.[22] To better understand the characteristics of CNDs, photophysical studies were performed. The dilute aqueous solution of CNDs (1 mg mL 1) showed a broad absorption spectrum (Figure 2 a) with peaks centered at 210 and 335 nm, and a hump around 370 nm, which represent the typical absorptions of an aromatic p system with extended conjugation in the CND structure. Further, the high energy tail in the visible region is attributed to Mie scattering caused by nanosized particles.[23] In the fluorescence spectrum (Figure 2 b), the CNDs showed emission maximum 412 nm when excited at 330 nm, and show a bright blue color under UV irradiation (385 nm) (Scheme 1). Excitation-independent photoluminescent behav-
Figure 1. PXRD profiles of ZIF-8 NP-derived CNDs a) before and b) after washing with aqueous HCl solution (5 vol %) and c) TEM and d) HAADFSTEM images of CNDs.
a typical (002) interlayer pack of graphite-type carbon, after washing with aqueous HCl solution followed by purification by using membrane dialysis (molecular weight cutoff 14 kDa). TEM and HAADFSTEM images displayed a uniform dispersion of CNDs with a mean particle diameter of 2.2 nm without apparent aggregation in water (Figure 2 c, d). HAADFSTEM and EDS analyses of randomly selected positions of CNDs display uniform compositions (Figure S1 in the Supporting Information). It should be noted that the carbonization temperature is a crucial factor for getting CNDs from ZIF-8 NPs. During carbonization, the zinc ions, the inorganic part of ZIF-8, turn to ZnO and the organic ligand MeIM becomes the carbon nanodots (Figure S2 in the Supporting Information). When the carbonization temperature was below 500 8C, the CND yield was very low, which can be attributed to the high thermal stability of ZIF-8 framework. On the other hand, if the carbonization temperature was above 600 8C, porous carbons were formed as in the previous works (Figure S3 in the Supporting Information).[14] The morphology of ZIF-8 is another crucial factor for getting CNDs. The CNDs &
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Figure 2. a) UV/Vis absorption spectrum; b) emission spectrum (lex = 330 nm) of an aqueous solution of CNDs; c) emission spectra of CNDs recorded for progressively longer excitation wavelength of 20 nm increments; and d) time-resolved fluorescence-decay curve of CNDs (lex = 375 nm) measured at 410 nm.
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Communication ior, which is rare in fluorescent carbon materials, was observed.[24] The maximum emission wavelength at different excitation wavelengths (Figure 2 c) remained at 412 nm, which can avoid autofluorescence during their applications.[25] The highest fluorescent intensity was observed at lex = 340 and 360 nm. The observed excitation-independent emission over the excitation wavelength range of 300–400 nm indicates a high degree of homogeneity with relatively uniform and well-passivated CND surface.[26] The CNDs can freely disperse in water without ultrasonication, looking transparent at low concentrations, and thus they can be called “water-soluble CNDs” (Scheme 1). The CNDs solution is very stable, and there was no nanoparticle precipitation in six months. Even at a very dilute concentration, the CND solution can emit bright blue light when it is irradiated by using a UV lamp (385 nm). This bright blue fluorescence of CNDs can be easily seen by naked eyes (Scheme 1). The fluorescence lifetime of CNDs was assessed by time-correlated single-photon counting (TCSPC) measurements. The lifetime data of these CNDs were very well fitted to a bi-exponential function (Figure 2 d). The observed lifetimes of the CNDs are 1.60 and 3.12 ns. The lifetime of CNDs in nanoseconds suggests that the synthesized CNDs are most suitable for optoelectronic and biological applications.[27] Usually, fluorescence is strongly quenched when the aqueous solutions of CNDs are deposited on solid substrates owing to the formation of aggregates.[9] However, the MOF-derived CNDs showed, interestingly, unaltered fluorescent emissions when deposited on paper. The paper was coated with an aqueous solution of CNDs and then dried in air. After drying, the paper was colorless as plain paper in normal daylight (Figure 3 a), and fluorescent as blue under a UV irradiation (385 nm; Figure 3 b). It should be noted that CNDs with a concentration as low as 1 10 6 mg mL 1 can give a fluorescence strong enough to be detected by naked eyes. Thus, we can apply these CNDs as fluorescent carbon inks for fluorescent patterning. Moreover, the prepared fluorescent pattern remains unchanged after six months in an indoor environment, exhibiting high potential for practical applications. It is reported that the water-soluble fluorescent CNDs are an ideal cell-imaging probe with minimum cytotoxicity.[28] However, functionalization is an important step for cellular and subcellular targeting.[29] Interestingly, we found our CNDs could be
very safe to the healthy cells and could only enter into weak/ dead cells without any further functionalization (Figure 3 c–e). The human cell line GM0637 was used, and the cells were transfected with a mammalian expression plasmid encoding H2 AX-eBAF-Y containing EYFP,[30] and were exposed in CNDadded medium for one hour. The GM0637 cell images were obtained under UV excitation (lex = 377 nm) for CNDs and blue excitations for EYFP (lex = 473 nm), and bright field (BF; Figure 3 c–e). By comparing the three images, we can easily understand that the EYFP positive cells are CND negative and vice versa. H2 AX-eBAF-Y is distributed in cellular nucleus, because the histone H2 AX is a member of core histone and contributes to nucleosome (i.e., a basic unit of DNA packaging in eukaryotes) formation. The expression plasmid also carries the antibiotic resistant gene, and thus EYFP positive cells are healthier, but the weaker or negative cells are also morphologically damaged by G418 exposure (BF). The fluorescent signals were only observed from the damaged and unhealthy cell after CND exposure. This result clearly evidences that the CNDs cannot be incorporated into normal cells, which are thus very safe to be used in various applications in day-to-day life. In summary, for the first time, we have utilized the metal–organic framework nanoparticles as a precursor to prepare water-soluble carbon nanodots (CNDs). Simple carbonization of the ZIF-8 NPs, prepared with ultrasonication, at a mild temperature (500 8C) gave carbon nanodots with strong and stable luminescence, of which the maximum emission wavelength is independent on the excitation wavelength in the range of 300-400 nm. The retention of fluorescence in the solid state and the ability to distinguish the weaker cells from the healthier cells open up avenues to applications of these MOF-derived CNDs in the field of biosafe fluorescent patterning.
Experimental Section Preparation of ZIF-8 NPs In a typical synthesis, zinc nitrate (Zn(NO3)2·6 H2O, 25 mmol, 7.435 g) was dissolved in methanol (500 mL). 2-Methylimidazole (MeIM, 25 mmol, 2.052 g) and triethylamine (TEA, 36 mmol, 3.267 g) were dissolved in methanol (500 mL) at RT (25 8C). These solutions were mixed while sonicating in a bath sonicator for 2 min and kept as such. The solution became turbid immediately. After 4 h, the turbid solution was centrifuged, washed five times with methanol, and dried at 80 8C for 4 h to get nanoparticles of ZIF-8.
Preparation of ZIF-8 NP-derived carbon nanodots (CNDs) The ZIF-8 NPs (0.25 g) were transferred into a ceramic boat and placed into a temperature-programmed furnace under an argon flow, heated from RT to 500 8C in 1 h, and then kept at 500 8C for 10 h and cooled to RT. The obtained material was added to HCl solution (200 mL, 5 vol % in water) to dissolve the ZnO formed along with carbon nanodots from ZIF-8 NPs. Thus prepared ZIF-8-derived carbon nanodots (CNDs) were purified by membrane dialysis (molecular weight cut off 14 kDa) against ultrapure water for two days. The outside water was changed every 6 h, and the obtained ZIF-8 NP-derived carbon nanodots, CNDs, were stored at RT for further studies.
Figure 3. CND-marked AIST logo on ordinary paper under a) daylight and b) UV light (lex = 385 nm), the H2 AX-eBAF-Y cell images showing the fluorescence from c) CNDs (lex = 377 nm); d) EYFP (lex = 473 nm), and e) the brightfield image. Chem. Eur. J. 2014, 20, 1 – 5
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Communication Biosafety test of CNDs
[13] a) H.-L. Jiang, Q. Xu, Chem. Commun. 2011, 47, 3351; b) S.-L. Li, Q. Xu, Energy Environ. Sci. 2013, 6, 1656; c) J.-K. Sun, Q. Xu, Energy Environ. Sci. DOI: 10.1039/c4ee00517a. [14] a) B. Liu, H. Shioyama, T. Akita, Q. Xu, J. Am. Chem. Soc. 2008, 130, 5390; b) D. S. Yuan, J. X. Chen, S. X. Tan, N. N. Xia, Y. L. Liu, Electrochem. Commun. 2009, 11, 1191; c) B. Liu, H. Shioyama, H.-L. Jiang, X. Zhang, Q. Xu, Carbon 2010, 48, 456; d) J. Hu, L. Wang, Q. M. Gao, H. L. Guo, Carbon 2010, 48, 3599; e) A. J. Amali, J.-K. Sun, Q. Xu, Chem. Commun. 2014, 50, 1519. [15] a) M. Hu, J. Reboul, S. Furukawa, L. Radhakrishnan, Y. Zhang, P. Srinivasu, H. Iwai, H. Wang, Y. Nemoto, N. Suzuki, S. Kitagawa, Y. Yamauchi, Chem. Commun. 2011, 47, 8124; b) L. Radhakrishnan, J. Reboul, S. Furukawa, P. Srinivasu, S. Kitagawa, Y. Yamauchi, Chem. Mater. 2011, 23, 1225; c) S. Ma, G. A. Goenaga, A. V. Call, D.-J. Liu, Chem. Eur. J. 2011, 17, 2063; d) P. Pachfule, B. P. Biswal, R. Banerjee, Chem. Eur. J. 2012, 18, 11399; e) M. Hu, J. Reboul, S. Furukawa, N. L. Torad, Q. Ji, P. Srinivasu, K. Ariga, S. Kitagawa, Y. Yamauchi, J. Am. Chem. Soc. 2012, 134, 2864; f) S. J. Yang, T. Kim, J. H. Im, Y. S. Kim, K. Lee, H. Jung, C. R. Park, Chem. Mater. 2012, 24, 464; g) S. Lim, K. Suh, Y. Kim, M. Yoon, H. Park, D. N. Dybtsev, K. Kim, Chem. Commun. 2012, 48, 7447; h) S. J. Yang, C. R. Park, Adv. Mater. 2012, 24, 4010. [16] a) H.-L. Jiang, B. Liu, Y.-Q. Lan, K. Kuratani, T. Akita, H. Shioyama, F. Zong, Q. Xu, J. Am. Chem. Soc. 2011, 133, 11854; b) W. Chaikittisilp, M. Hu, H. Wang, H.-S. Huang, T. Fujita, K. C.-W. Wu, L.-C. Chen, Y. Yamauchi, K. Ariga, Chem. Commun. 2012, 48, 7259; c) A. Almasoudi, R. Mokaya, J. Mater. Chem. 2012, 22, 146; d) N. L. Torad, M. Hu, Y. Kamachi, K. Takai, M. Imura, M. Naitoa, Y. Yamauchi, Chem. Commun. 2013, 49, 2521. [17] a) K. S. Park, Z. Ni, A. P. Ct, J. Y. Choi, R. Huang, F. J. Uribe-Romo, H. K. Chae, M. Keeffe, O. M. Yaghi, Proc. Natl. Acad. Sci. USA 2006, 103, 10186; b) X. C. Huang, Y. Y. Lin, J. P. Zhang, X. M. Chen, Angew. Chem. 2006, 118, 1587; Angew. Chem. Int. Ed. 2006, 45, 1557. [18] See the Supporting Information. [19] S. Liu, J. Tian, L. Wang, Y. Luo, W. Lu, X. Sun, Biosens. Bioelectron. 2011, 26, 4491. [20] S. Fleutot, J.-C. Dupin, G. Renaudin, H. Martinez, Phys. Chem. Chem. Phys. 2011, 13, 17564. [21] M. Sevilla, A. B. Fuertes, Chem. Eur. J. 2009, 15, 4195. [22] S. N. Baker, G. A. Baker, Angew. Chem. 2010, 122, 6876; Angew. Chem. Int. Ed. 2010, 49, 6726. [23] a) G. S. He, L. X. Yuan, J. D. Bhawalka, P. N. Prasad, Appl. Opt. 1997, 36, 3387; b) G. S. He, J. Swiatkiewicz, Y. Jiang, P. N. Prasad, B. A. Reinhardt, L. S. Tan, R. Kannan, J. Phys. Chem. A 2000, 104, 4805; c) G. S. He, Q. D. Zheng, C. G. Lu, P. N. Prasad, IEEE. J. Quantum. Electron. 2005, 41, 1037; d) Q. D. Zheng, S. K. Gupta, G. S. He, L. S. Tan, P. N. Prasad, Adv. Funct. Mater. 2008, 18, 2770; e) G. S. He, K. T. Yong, J. Zhu, H. Y. Qin, P. N. Prasad, IEEE. J. Quantum. Electron. 2010, 46, 931. [24] a) R. Liu, D. Wu, S. Liu, K. Koynov, W. Knoll, Q. Li, Angew. Chem. 2009, 121, 4668; Angew. Chem. Int. Ed. 2009, 48, 4598; b) D. Pan, J. Zhang, Z. Li, C. Wu, X. Yan, M. Wu, Chem. Commun. 2010, 46, 3681; c) M. J. Krysmann, A. Kelarakis, P. Dallas, E. P. Giannelis, J. Am. Chem. Soc. 2012, 134, 747; d) X. Zhai, P. Zhang, C. Liu, T. Bai, W. Li, L. Dai, W. Liu, Chem. Commun. 2012, 48, 7955. [25] Y. Guo, Z. Wang, H. Shao, X. Jiang, Carbon 2013, 52, 583. [26] J. C. Vinci, I. M. Ferrer, S. J. Seedhouse, A. K. Bourdon, J. M. Reynard, B. A. Foster, F. V. Bright, L. A. Coln, J. Phys. Chem. Lett. 2013, 4, 239. [27] J. Peng, W. Gao, B. K. Gupta, Z. Liu, R. R. Aburto, L. Ge, L. Song, L. B. Alemany, X. Zhan, G. Gao, S. A. Vithayathil, B. A. Kaipparettu, A. A. Marti, T. Hayashi, J.-J. Zhu, P. M. Ajayan, Nano Lett. 2012, 12, 844. [28] S. J. Yu, M. W. Kang, H. C. Chang, K. M. Chen, Y. C. Yu, J. Am. Chem. Soc. 2005, 127, 17604. [29] Y. P. Sun, B. Zhou, Y. Lin, W. Wang, K. A. S. Fernando, P. Pathak, M. J. Meziani, B. A. Harruff, X. Wang, H. F. Wang, P. J. G. Luo, H. Yang, M. E. Kose, B. L. Chen, L. M. Veca, S. Y. Xie, J. Am. Chem. Soc. 2006, 128, 7756. [30] H. Hoshino, Y. Nakajima, Y. Ohmiya, Nat. Methods 2007, 4, 637.
Human cell line GM0637 was maintained in 10 % fetal bovine serum (FBS) supplemented DMEM at 37 8C, and seeded in six-well dishes 24 h before transfection. The cells were transfected with a mammalian expression plasmid encoding H2 AX-eBAF-Y, by using Lipofectamin 2000 (INVITROGEN).[30] After 9 h, the cells were reseeded onto a 35 mm glass-based dish (27 mm F, IWAKI) and cultured in 10 % FBS DMEM containing 500 mg mL 1 G418. After further incubation for 24 h, the carbon nanodots (CNDs) were added into the medium to final concentration of 5 mg mL 1, and the cells were exposed to the CNDs for 1 h. Then the cells were washed twice with fresh medium and replaced with phenol red free 10 % FBS DMEM. Fluorescence images of live cells were acquired with a Biorevo (BZ-9000; KEYENCE) equipped with a 40 1.0 NA objective (Nikon).
Acknowledgements The authors acknowledge Dr. T. Uchida for TEM measurements and AIST for financial support. A.J.A. thanks AIST for a postdoctoral fellowship. Keywords: carbon · fluorescent probes · metal–organic frameworks · nanodots · quantum dots [1] a) H. Li, Z. Kang, Y. Liu, S.-T. Lee, J. Mater. Chem. 2012, 22, 24230; b) L. C. Cheng, X. M. Jiang, J. Wang, C. Y. Chen, R. S. Liu, Nanoscale 2013, 5, 3547. [2] S. Zhu, S. Tang, J. Zhang, B. Yang, Chem. Commun. 2012, 48, 4527. [3] X. Xu, R. Ray, Y. Gu, H. J. Ploehn, L. Gearheart, K. Raker, W. A. Scrivens, J. Am. Chem. Soc. 2004, 126, 12736. [4] S.-L. Hu, K.-Y. Niu, J. Sun, J. Yang, N.-Q. Zhao, X.-W. Du, J. Mater. Chem. 2009, 19, 484. [5] a) J. Zhou, C. Booker, R. Li, X. Zhou, T.-K. Sham, X. Sun, Z. Ding, J. Am. Chem. Soc. 2007, 129, 744; b) L. Zheng, Y. Chi, Y. Dong, J. Lin, B. Wang, J. Am. Chem. Soc. 2009, 131, 4564. [6] a) H. Zhu, X. Wang, Y. Li, Z. Wang, F. Yang, X. Yang, Chem. Commun. 2009, 5118; b) A. Jaiswal, S. S. Ghosh, A. Chattopadhyay, Chem. Commun. 2012, 48, 407. [7] a) H. Liu, T. Ye, C. Mao, Angew. Chem. 2007, 119, 6593; Angew. Chem. Int. Ed. 2007, 46, 6473; b) Y. Yang, J. Cui, M. Zheng, C. Hu, S. Tan, Y. Xiao, Q. Yang, Y. Liu, Chem. Commun. 2012, 48, 380; c) C. Zhu, J. Zhai, S. Dong, Chem. Commun. 2012, 48, 9367. [8] a) D. Pan, J. Zhang, Z. Li, M. Wu, Adv. Mater. 2010, 22, 734; b) Y. Dong, R. Wang, H. Li, J. Shao, Y. Chi, X. Lin, G. Chen, Carbon 2012, 50, 2810. [9] S. Qu, X. Wang, Q. Lu, X. Liu, L. Wang, Angew. Chem. 2012, 124, 12381; Angew. Chem. Int. Ed. 2012, 51, 12215. [10] a) M. Eddaoudi, J. Kim, N. Rosi, D. Vodak, J. Wachter, M. Keeffe, O. M. Yaghi, Science 2002, 295, 469; b) J.-P. Zhang, X.-C. Huang, X.-M. Chen, Chem. Soc. Rev. 2009, 38, 2385; c) G. Frey, C. Serre, Chem. Soc. Rev. 2009, 38, 1380; d) D. Yuan, D. Zhao, D. Sun, H.-C. Zhou, Angew. Chem. 2010, 122, 5485; Angew. Chem. Int. Ed. 2010, 49, 5357; e) B. Chen, S. Xiang, G. Qian, Acc. Chem. Res. 2010, 43, 1115; f) T. Wu, L. Wang, X. Bu, V. Chau, P. Feng, J. Am. Chem. Soc. 2012, 134, 4517. [11] a) S. K. Ghosh, S. Bureekaew, S. Kitagawa, Angew. Chem. 2008, 120, 3451; Angew. Chem. Int. Ed. 2008, 47, 3403; b) L. Ma, A. Jin, Z. Xie, W. Lin, Angew. Chem. 2009, 121, 10089; Angew. Chem. Int. Ed. 2009, 48, 9905; c) J. Lee, O. K. Farha, J. Roberts, K. A. Scheidt, S. T. Nguyen, J. T. Hupp, Chem. Soc. Rev. 2009, 38, 1450; d) S. Motoyama, R. Makiura, O. Sakata, H. Kitagawa, J. Am. Chem. Soc. 2011, 133, 5640; e) M. M. Wanderley, C. Wang, C.-D. Wu, W. Lin, J. Am. Chem. Soc. 2012, 134, 9050. [12] a) J. S. Seo, D. Whang, H. Lee, S. I. Jun, J. Oh, Y. J. Jeon, K. Kim, Nature 2000, 404, 982; b) S. Kitagawa, R. Kitaura, S. Noro, Angew. Chem. 2004, 116, 2388; Angew. Chem. Int. Ed. 2004, 43, 2334.
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Communication
COMMUNICATION & Fluorescent Probes
Highly photoluminescent carbon nanodots (CNDs) were synthesized for the first time from metal–organic framework (ZIF-8) nanoparticles. Coupled with fluorescence and non-toxic characteristics, these carbon nanodots could potentially be used in biosafe color patterning (see figure).
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A. J. Amali, H. Hoshino, C. Wu, M. Ando, Q. Xu* && – && From Metal–Organic Framework to Intrinsically Fluorescent Carbon Nanodots
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