- Email: [email protected]
Photodynamic release of fullerenes from within carbon nanohorn
Chemical Physics Letters 456 (2008) 220–222
Contents lists available at ScienceDirect
Chemical Physics Letters journal homepage: www.elsevier.com/locate/cplett
Photodynamic release of fullerenes from within carbon nanohorn Eijiro Miyako *, Hideya Nagata, Ken Hirano, Yoji Makita, Takahiro Hirotsu Health Technology Research Center, National Institute of Advanced Industrial Science and Technology (AIST), Hayashi-cho, Takamatsu 761 0395, Japan
a r t i c l e
i n f o
Article history: Received 20 February 2008 In final form 17 March 2008 Available online 24 March 2008
a b s t r a c t We have found that oxidized single-wall carbon nanohorns (SWNHox) can exhibit a near-infrared (NIR) laser-triggered accelerated release of encapsulated fullerenes (C60) from within their inner nanospaces. After the NIR laser irradiation of an aqueous SWNHox encapsulating C60 solution/toluene biphasic system, C60 molecules are enriched in the toluene phase. NIR laser-driven SWNHs encapsulating substrates could initiate the development of a new range of drug-delivery systems. Ó 2008 Elsevier B.V. All rights reserved.
1. Introduction A single-wall carbon nanohorn (SWNH) is a recently recognized member of the nanocarbon family [1]. SWNHs are aggregates of graphitic tubes with closed ends and cone-shaped caps (horns). Each tube has a diameter of 2–5 nm, and the aggregated tubes form spherical structures (approximately 80–100 nm in diameter). In addition, oxidation and acid treatment can create nanopores in the walls of SWNHs through which small molecules (<2 nm) can be absorbed into or released from the interior space [2,3]; a specific example of such a small molecule is fullerene (C60), whose derivative is known to inhibit an enzyme responsible for increasing HIV virion proteins [11]. Furthermore, SWNHs do not have toxicant metal impurities because they are produced without a metal catalyst by a laser ablation method [12]. Although SWNHs appear to be very attractive nanomaterials for biomedical fields, applications and physical properties of SWNH have not been satisfactorily investigated with the exception of studies about the substrate supporting materials [5–10]. In addition, the substrate-releasing behavior of SWNHs in aqueous media is very slow because encapsulated substrates are generally insoluble in an aqueous solution [8–10]. We have recently developed a nanoheating system based on near-infrared (NIR) laser-driven SWNHs for the selective elimination of various microorganisms (yeast, bacteria and virus) [2,3]. The mechanism of the NIR laser-triggered exothermy of SWNHs is probably due to the rapid transfer of their optically stimulated electronic excitations to molecular vibration energies, which generates heat [2,3]. Here, we consider that the NIR laser-driven powerful photothermal conversion phenomenon of SWNHs has the
* Corresponding author. Fax: +81 87 869 3550. E-mail address: [email protected] (E. Miyako). 0009-2614/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.cplett.2008.03.044
potential to exert a force on encapsulated substrates in the SWNHs. The construction of nanocarriers, which is possible in order to release the desired quantity of drugs into the targeted area, is one of the main functions of nanomedicine [13]. In the present study, we demonstrate that NIR laser-triggered SWNHs can exhibit an accelerated release of encapsulated C60 molecules as a model drug from within their inner nanospaces (Fig. 1).
2. Experimental The nanopores in the SWNHs (purity = 95%, metal-free) (supplied by NEC) were produced by oxygen gas treatment [7]. We denote an oxygen-gas-treated SWNH as SWNHox, and SWNHoxencapsulated C60 as C60@SWNHox. SWNHox and C60@SWNHox (the starting quantity of C60 (Tokyo Chemical Industry) on SWNHox was 15 wt%) were prepared by the nanoprecipitation method [7] (see Fig. 2). The incorporation of C60 inside the SWNHox was observed by transmission electron microscopy (TEM) (JEM-3010; JEOL) (acceleration voltage: 200 kV). The quantity of incorporated C60 was estimated by the thermogravimetry-differential thermal analysis (TGDTA) (Mac Science, TG-DTA 2000) of C60@SWNHox carried out in an oxygen atmosphere from room temperature to 1000 °C. X-ray diffraction (XRD) (Rigaku, RINT-2100 V) was used to confirm that C60 was not located outside the SWNHox. Ultraviolet–visible (UV–vis) absorption spectra (V-630; Jasco) were measured to estimate the amount of C60 released from C60@SWNHox into toluene (Wako). In this study, C60@SWNHox was sonicated for 15 min in distilled water at a concentration of 250 lg mL–1. Next, toluene (2 mL) was slowly added to the C60@SWNHox aqueous solution (1 mL) in a quartz-type cuvette (optical path = 1 cm). We irradiated the C60@SWNHox aqueous solution by a 1064 nm continuous wave Nd:YAG laser (TEM00,
E. Miyako et al. / Chemical Physics Letters 456 (2008) 220–222
221
Fig. 1. Concept of accelerated release of C60 molecules from within SWNHox.
maximum power = 10 W) (IPG Laser GmbH, YLM-10-1064-LP) at 5 W for 1–3 min; toluene was not irradiated because it is a highly flammable and volatile solvent. The setup for this study is described in detail in our previous study (refer to the supplementary videograph) [2,3]. The quantity of released C60 was estimated from the maximum absorbance at 336 nm due to C60 (Fig. S3) [7]. After irradiation (13 min), the supernatant toluene phase (1 mL) was sampled and its UV–vis spectrum was measured; further, we also measured the temperature of the C60@SWNHox aqueous solution (not directly under the laser beam) using a mercury thermometer. For TEM observations, we irradiated a C60@SWNHox aqueous solution (250 lg mL–1) (1 mL) at 1 W for 60 min using the same setup (see Fig 3). 3. Results and discussion The encapsulation of C60 molecules inside the SWNHox was confirmed by TEM and XRD analysis (Figs. 2a, b and S1). By these TEM and XRD characterizations, we can observe that there are many C60 molecules in the nanospaces of the SWNHox. From the TG-DTA, the quantity of encapsulated C60 molecules is approximately 13.4 wt% for SWNHox (Fig. S2). It should be noted that pristine SWNHs do not encapsulate C60 molecules at all because of the absence of nanopores in the walls (Fig. S1). After the NIR laser-irradiation (5 W, 1–3 min) of an aqueous C60@SWNHox/toluene biphasic system, C60 molecules are enriched in the toluene phase (Figs. 3 and S3). In contrast, very few C60 molecules are released after incubation at 40 and 60 °C for 13 min (Figs. 3 and S3). In a control experiment performed at room temperature, there is no release of C60 at all with either incubation time (Figs. 3 and S3). The following two physical mechanisms are responsible for the release of C60 molecules from within the
Fig. 3. Concentration of C60 released from C60@SWNHox into toluene. Three tests of each sample were averaged; error bars indicate the standard deviations. *N.D.: Not determined because no C60 was detected.
SWNHoxs during the NIR laser irradiation. The first is the mechanical actuation of a photoinduced SWNHox [14,15]. We have observed extraordinary photothermal conversion phenomena [16] such as thermal radiation from SWNHoxs, laser breakdown (photoacoustic effect), and plasma-generation phenomena when the aqueous C60@SWNHox/toluene biphasic system is irradiated by an NIR laser (refer to supplementary videograph). The other mechanism is the expansion of compounds inside the SWNHox with increasing bulk temperature [17,18]. The temperature of the aqueous C60@SWNHox solution changes from 25 °C to 58 °C by the NIR laser irradiation (5 W, 3 min). The local temperature around C60@SWNHoxs is probably considerably higher (greater than at least 58 °C) as a result of the abovementioned photothermal conversion phenomenon. We also consider that the convection or turbulence of water derived from the local heating around the SWNHox with the laser can increase the dissolution of C60 into the toluene and the chances of C60@SWNHox to come close to the toluene–water boundary. From the NIR laser irradiation of aqueous C60@SWNHox (singlephase system, 1 W, 60 min), we confirm that a number of C60 molecules (c.a. 1 nm) are deposited on the side walls of the SWNHox (Fig. 4a). The released C60 molecules are probably bound to the wall of the SWNHox through noncovalent interactions [19] because C60 is insoluble in water. Furthermore, when the single-phase system is incubated for 60 min at 60 °C or at room temperature, barely a few C60 molecules are released from the wall of the SWNHox (Fig. 4b and c). These results clearly demonstrate that SWNHox can exhibit an NIR laser-triggered stimulated release of encapsulated C60 from within their inner nanospaces.
Fig. 2. Nanostructures of SWNHox and C60@SWNHox: (a) TEM image of SWNHox. (b) TEM image of C60@SWNHox.
222
E. Miyako et al. / Chemical Physics Letters 456 (2008) 220–222
Fig. 4. (a, b) TEM images of C60@SWNHox after NIR laser irradiation (1064 nm, 1 W, 60 min). The arrows show the released C60 molecules. (c) TEM image of C60@SWNHox after incubation at 60 °C for 60 min. (d) TEM image of C60@SWNHox after incubation at room temperature for 60 min. The acceleration voltage for all TEM observations was 200 kV.
4. Concluding remarks
References
In conclusion, we have demonstrated that C60 molecules encapsulated in SWNHox can be released by NIR laser irradiation. These results strongly suggest that SWNHs are potentially useful for a photocontrolled release of drugs. We have recently reported that molecular recognition element-SWNH conjugates have the potential to serve as a highly-selective NIR laser-triggered exothermic antimicrobial agents as mentioned above [2,3]. Construction of multifunctional nanomaterials, which work for not only photothermally deactivation of microbes but also a photocontrolled release of various drugs, is one of the main goals of nanomedicine. We believe that our present work makes an important progress for novel application of SWNH.
[1] S. Iijima, M. Yudasaka, R. Yamada, S. Bandow, K. Suenaga, F. Kokai, K. Takahashi, Chem. Phys. Lett. 309 (1999) 165. [2] E. Miyako, H. Nagata, K. Hirano, Y. Makita, K. Nakayama, T. Hirotsu, Nanotechnology 18 (2007) 475103. [3] E. Miyako, H. Nagata, K. Hirano, K. Sakamoto, Y. Makita, K. Nakayama, T. Hirotsu, Nanotechnology 19 (2008) 075106. [5] J. Miyawaki, M. Yudasaka, H. Imai, H. Yorimitsu, H. Isobe, E. Nakamura, S. Iijima, Adv. Mater. 18 (2006) 1010. [6] R. Yuge, T. Ichihashi, Y. Shimakawa, Y. Kubo, M. Yudasaka, S. Iijima, Adv. Mater. 16 (2004) 1420. [7] R. Yuge et al., J. Phys. Chem. B 109 (2005) 17861. [8] T. Murakami, J. Fan, M. Yudasaka, S. Iijima, K. Shiba, Mol. Pharm. 3 (2006) 407. [9] K. Ajima, A. Maigné, M. Yudasaka, S. Iijima, J. Phys. Chem. B 110 (2006) 19097. [10] K. Ajima, M. Yudasaka, T. Murakami, A. Maigné, K. Shiba, S. Iijima, Mol. Pharm. 6 (2005) 475. [11] R. Sijbesma et al., J. Am. Chem. Soc. 115 (1993) 6510. [12] H. Isobe et al., Angew. Chem. Int. Ed. 45 (2006) 6676. [13] N.K. Mal, M. Fujiwara, Y. Tanaka, Nature 421 (2003) 350. [14] P.M. Ajayan et al., Science 296 (2002) 705. [15] S.V. Ahir, E.M. Terentjev, Nat. Mater. 4 (2005) 491. [16] K.J. Wilkinson, J.R. Lead, Environmental Colloids and Particles: Behaviour, Separation and Characterisation, Wiley-VCH, Weinheim, 2007. [17] Y. Maniwa et al., Chem. Phys. Lett. 401 (2005) 534. [18] Y. Gao, Y. Bando, Nature 415 (2002) 599. [19] D.A. Britz, A.N. Khlobystov, Chem. Soc. Rev. 35 (2006) 637.
Acknowledgements We are grateful to NEC (Japan) for providing the carbon nanohorn. We also thank all members of the Health Technology Research Center for their help and advice. Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.cplett.2008.03.044.
Contents lists available at ScienceDirect
Chemical Physics Letters journal homepage: www.elsevier.com/locate/cplett
Photodynamic release of fullerenes from within carbon nanohorn Eijiro Miyako *, Hideya Nagata, Ken Hirano, Yoji Makita, Takahiro Hirotsu Health Technology Research Center, National Institute of Advanced Industrial Science and Technology (AIST), Hayashi-cho, Takamatsu 761 0395, Japan
a r t i c l e
i n f o
Article history: Received 20 February 2008 In final form 17 March 2008 Available online 24 March 2008
a b s t r a c t We have found that oxidized single-wall carbon nanohorns (SWNHox) can exhibit a near-infrared (NIR) laser-triggered accelerated release of encapsulated fullerenes (C60) from within their inner nanospaces. After the NIR laser irradiation of an aqueous SWNHox encapsulating C60 solution/toluene biphasic system, C60 molecules are enriched in the toluene phase. NIR laser-driven SWNHs encapsulating substrates could initiate the development of a new range of drug-delivery systems. Ó 2008 Elsevier B.V. All rights reserved.
1. Introduction A single-wall carbon nanohorn (SWNH) is a recently recognized member of the nanocarbon family [1]. SWNHs are aggregates of graphitic tubes with closed ends and cone-shaped caps (horns). Each tube has a diameter of 2–5 nm, and the aggregated tubes form spherical structures (approximately 80–100 nm in diameter). In addition, oxidation and acid treatment can create nanopores in the walls of SWNHs through which small molecules (<2 nm) can be absorbed into or released from the interior space [2,3]; a specific example of such a small molecule is fullerene (C60), whose derivative is known to inhibit an enzyme responsible for increasing HIV virion proteins [11]. Furthermore, SWNHs do not have toxicant metal impurities because they are produced without a metal catalyst by a laser ablation method [12]. Although SWNHs appear to be very attractive nanomaterials for biomedical fields, applications and physical properties of SWNH have not been satisfactorily investigated with the exception of studies about the substrate supporting materials [5–10]. In addition, the substrate-releasing behavior of SWNHs in aqueous media is very slow because encapsulated substrates are generally insoluble in an aqueous solution [8–10]. We have recently developed a nanoheating system based on near-infrared (NIR) laser-driven SWNHs for the selective elimination of various microorganisms (yeast, bacteria and virus) [2,3]. The mechanism of the NIR laser-triggered exothermy of SWNHs is probably due to the rapid transfer of their optically stimulated electronic excitations to molecular vibration energies, which generates heat [2,3]. Here, we consider that the NIR laser-driven powerful photothermal conversion phenomenon of SWNHs has the
* Corresponding author. Fax: +81 87 869 3550. E-mail address: [email protected] (E. Miyako). 0009-2614/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.cplett.2008.03.044
potential to exert a force on encapsulated substrates in the SWNHs. The construction of nanocarriers, which is possible in order to release the desired quantity of drugs into the targeted area, is one of the main functions of nanomedicine [13]. In the present study, we demonstrate that NIR laser-triggered SWNHs can exhibit an accelerated release of encapsulated C60 molecules as a model drug from within their inner nanospaces (Fig. 1).
2. Experimental The nanopores in the SWNHs (purity = 95%, metal-free) (supplied by NEC) were produced by oxygen gas treatment [7]. We denote an oxygen-gas-treated SWNH as SWNHox, and SWNHoxencapsulated C60 as C60@SWNHox. SWNHox and C60@SWNHox (the starting quantity of C60 (Tokyo Chemical Industry) on SWNHox was 15 wt%) were prepared by the nanoprecipitation method [7] (see Fig. 2). The incorporation of C60 inside the SWNHox was observed by transmission electron microscopy (TEM) (JEM-3010; JEOL) (acceleration voltage: 200 kV). The quantity of incorporated C60 was estimated by the thermogravimetry-differential thermal analysis (TGDTA) (Mac Science, TG-DTA 2000) of C60@SWNHox carried out in an oxygen atmosphere from room temperature to 1000 °C. X-ray diffraction (XRD) (Rigaku, RINT-2100 V) was used to confirm that C60 was not located outside the SWNHox. Ultraviolet–visible (UV–vis) absorption spectra (V-630; Jasco) were measured to estimate the amount of C60 released from C60@SWNHox into toluene (Wako). In this study, C60@SWNHox was sonicated for 15 min in distilled water at a concentration of 250 lg mL–1. Next, toluene (2 mL) was slowly added to the C60@SWNHox aqueous solution (1 mL) in a quartz-type cuvette (optical path = 1 cm). We irradiated the C60@SWNHox aqueous solution by a 1064 nm continuous wave Nd:YAG laser (TEM00,
E. Miyako et al. / Chemical Physics Letters 456 (2008) 220–222
221
Fig. 1. Concept of accelerated release of C60 molecules from within SWNHox.
maximum power = 10 W) (IPG Laser GmbH, YLM-10-1064-LP) at 5 W for 1–3 min; toluene was not irradiated because it is a highly flammable and volatile solvent. The setup for this study is described in detail in our previous study (refer to the supplementary videograph) [2,3]. The quantity of released C60 was estimated from the maximum absorbance at 336 nm due to C60 (Fig. S3) [7]. After irradiation (13 min), the supernatant toluene phase (1 mL) was sampled and its UV–vis spectrum was measured; further, we also measured the temperature of the C60@SWNHox aqueous solution (not directly under the laser beam) using a mercury thermometer. For TEM observations, we irradiated a C60@SWNHox aqueous solution (250 lg mL–1) (1 mL) at 1 W for 60 min using the same setup (see Fig 3). 3. Results and discussion The encapsulation of C60 molecules inside the SWNHox was confirmed by TEM and XRD analysis (Figs. 2a, b and S1). By these TEM and XRD characterizations, we can observe that there are many C60 molecules in the nanospaces of the SWNHox. From the TG-DTA, the quantity of encapsulated C60 molecules is approximately 13.4 wt% for SWNHox (Fig. S2). It should be noted that pristine SWNHs do not encapsulate C60 molecules at all because of the absence of nanopores in the walls (Fig. S1). After the NIR laser-irradiation (5 W, 1–3 min) of an aqueous C60@SWNHox/toluene biphasic system, C60 molecules are enriched in the toluene phase (Figs. 3 and S3). In contrast, very few C60 molecules are released after incubation at 40 and 60 °C for 13 min (Figs. 3 and S3). In a control experiment performed at room temperature, there is no release of C60 at all with either incubation time (Figs. 3 and S3). The following two physical mechanisms are responsible for the release of C60 molecules from within the
Fig. 3. Concentration of C60 released from C60@SWNHox into toluene. Three tests of each sample were averaged; error bars indicate the standard deviations. *N.D.: Not determined because no C60 was detected.
SWNHoxs during the NIR laser irradiation. The first is the mechanical actuation of a photoinduced SWNHox [14,15]. We have observed extraordinary photothermal conversion phenomena [16] such as thermal radiation from SWNHoxs, laser breakdown (photoacoustic effect), and plasma-generation phenomena when the aqueous C60@SWNHox/toluene biphasic system is irradiated by an NIR laser (refer to supplementary videograph). The other mechanism is the expansion of compounds inside the SWNHox with increasing bulk temperature [17,18]. The temperature of the aqueous C60@SWNHox solution changes from 25 °C to 58 °C by the NIR laser irradiation (5 W, 3 min). The local temperature around C60@SWNHoxs is probably considerably higher (greater than at least 58 °C) as a result of the abovementioned photothermal conversion phenomenon. We also consider that the convection or turbulence of water derived from the local heating around the SWNHox with the laser can increase the dissolution of C60 into the toluene and the chances of C60@SWNHox to come close to the toluene–water boundary. From the NIR laser irradiation of aqueous C60@SWNHox (singlephase system, 1 W, 60 min), we confirm that a number of C60 molecules (c.a. 1 nm) are deposited on the side walls of the SWNHox (Fig. 4a). The released C60 molecules are probably bound to the wall of the SWNHox through noncovalent interactions [19] because C60 is insoluble in water. Furthermore, when the single-phase system is incubated for 60 min at 60 °C or at room temperature, barely a few C60 molecules are released from the wall of the SWNHox (Fig. 4b and c). These results clearly demonstrate that SWNHox can exhibit an NIR laser-triggered stimulated release of encapsulated C60 from within their inner nanospaces.
Fig. 2. Nanostructures of SWNHox and C60@SWNHox: (a) TEM image of SWNHox. (b) TEM image of C60@SWNHox.
222
E. Miyako et al. / Chemical Physics Letters 456 (2008) 220–222
Fig. 4. (a, b) TEM images of C60@SWNHox after NIR laser irradiation (1064 nm, 1 W, 60 min). The arrows show the released C60 molecules. (c) TEM image of C60@SWNHox after incubation at 60 °C for 60 min. (d) TEM image of C60@SWNHox after incubation at room temperature for 60 min. The acceleration voltage for all TEM observations was 200 kV.
4. Concluding remarks
References
In conclusion, we have demonstrated that C60 molecules encapsulated in SWNHox can be released by NIR laser irradiation. These results strongly suggest that SWNHs are potentially useful for a photocontrolled release of drugs. We have recently reported that molecular recognition element-SWNH conjugates have the potential to serve as a highly-selective NIR laser-triggered exothermic antimicrobial agents as mentioned above [2,3]. Construction of multifunctional nanomaterials, which work for not only photothermally deactivation of microbes but also a photocontrolled release of various drugs, is one of the main goals of nanomedicine. We believe that our present work makes an important progress for novel application of SWNH.
[1] S. Iijima, M. Yudasaka, R. Yamada, S. Bandow, K. Suenaga, F. Kokai, K. Takahashi, Chem. Phys. Lett. 309 (1999) 165. [2] E. Miyako, H. Nagata, K. Hirano, Y. Makita, K. Nakayama, T. Hirotsu, Nanotechnology 18 (2007) 475103. [3] E. Miyako, H. Nagata, K. Hirano, K. Sakamoto, Y. Makita, K. Nakayama, T. Hirotsu, Nanotechnology 19 (2008) 075106. [5] J. Miyawaki, M. Yudasaka, H. Imai, H. Yorimitsu, H. Isobe, E. Nakamura, S. Iijima, Adv. Mater. 18 (2006) 1010. [6] R. Yuge, T. Ichihashi, Y. Shimakawa, Y. Kubo, M. Yudasaka, S. Iijima, Adv. Mater. 16 (2004) 1420. [7] R. Yuge et al., J. Phys. Chem. B 109 (2005) 17861. [8] T. Murakami, J. Fan, M. Yudasaka, S. Iijima, K. Shiba, Mol. Pharm. 3 (2006) 407. [9] K. Ajima, A. Maigné, M. Yudasaka, S. Iijima, J. Phys. Chem. B 110 (2006) 19097. [10] K. Ajima, M. Yudasaka, T. Murakami, A. Maigné, K. Shiba, S. Iijima, Mol. Pharm. 6 (2005) 475. [11] R. Sijbesma et al., J. Am. Chem. Soc. 115 (1993) 6510. [12] H. Isobe et al., Angew. Chem. Int. Ed. 45 (2006) 6676. [13] N.K. Mal, M. Fujiwara, Y. Tanaka, Nature 421 (2003) 350. [14] P.M. Ajayan et al., Science 296 (2002) 705. [15] S.V. Ahir, E.M. Terentjev, Nat. Mater. 4 (2005) 491. [16] K.J. Wilkinson, J.R. Lead, Environmental Colloids and Particles: Behaviour, Separation and Characterisation, Wiley-VCH, Weinheim, 2007. [17] Y. Maniwa et al., Chem. Phys. Lett. 401 (2005) 534. [18] Y. Gao, Y. Bando, Nature 415 (2002) 599. [19] D.A. Britz, A.N. Khlobystov, Chem. Soc. Rev. 35 (2006) 637.
Acknowledgements We are grateful to NEC (Japan) for providing the carbon nanohorn. We also thank all members of the Health Technology Research Center for their help and advice. Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.cplett.2008.03.044.