7972
J. Phys. Chem. C 2008, 112, 7972–7977
Optically and Magnetically Doped Organically Modified Silica Nanoparticles as Efficient Magnetically Guided Biomarkers for Two-Photon Imaging of Live Cancer Cells† Wing-Cheung Law,‡ Ken-Tye Yong,‡ Indrajit Roy,‡ GaiXia Xu,‡ Hong Ding,‡ Earl J. Bergey,‡ Hao Zeng,§ and Paras N. Prasad*,‡ Institute for Lasers, Photonics and Biophotonics and Department of Electrical Engineering, The State UniVersity of New York at Buffalo, Buffalo, New York 14260-4200, and Department of Physics, The State UniVersity of New York at Buffalo, Buffalo, New York 14260-4200 ReceiVed: December 26, 2007; ReVised Manuscript ReceiVed: February 12, 2008
We report here solution-phase synthesis of multifunctional nanoprobes for imaging live cancer cells. More specifically, quantum dots (QDs) and magnetite (Fe3O4) nanoparticles were coencapsulated within organically modified silica (ORMOSIL) nanoparticles. These optically and magnetically doped ORMOSIL nanoparticles were systematically characterized. These ORMOSIL nanoparticles were used for magnetically guided in Vitro delivery to a human cancer cell line. Two-photon imaging was used to confirm the uptake of nanoparticledoped ORMOSIL nanoparticles into the cancer cells. We also demonstrate that synergistic interaction of both magnetic targeting and transferrin-receptor (TfR)-mediated targeting results in robust in Vitro cellular uptake, which is significantly higher than that obtained using these two targeting modes individually. Our cell viability study indicates them to be nontoxic. The results illustrate a promising biocompatible nanoparticle platform where multiple imaging and targeting agents can be coincorporated, with the purpose of efficient two-photon bioimaging and magnetically assisted targeting. Introduction For the past decade, semiconductor quantum dots (QDs) have been extensively used as a potential luminescence marker for biological applications ranging from cell labeling to fluorescence resonance energy transfer (FRET).1,2 QDs have become a powerful labeling tool because they possess the unique optical property of tuning their emission spectrum by simply varying their size and shape. Because of their high resistance to photobleaching, narrow emission spectra, broad excitation spectra, and longer fluorescence lifetime, many studies have suggested that QDs have potential to replace the organic dyes as optical probes for bioimaging.3–13 However, potential heavy metal toxicity as a result of leakage of constituent ions (e.g., cadmium, mercury, lead, etc.) from the QDs is one of the major concerns regarding their biomedical applications. For the past several years, studies in our laboratory have shown that quantum dot core-shell structures exhibit strong two-photon excited emission, making them well suited for twophoton bioimaging.14 The use of QDs for two-photon bioimaging offers the advantage of reduced photodamage and multiplexing ability, the latter due to their narrow emission peak. In addition, two-photon imaging provides improved depth penetration, and reduced background cellular autofluorescence.15 This is because (i) two-photon excitation occurs only at the focal point that prevents the out-of-focus contribution, and (ii) the required average laser power is low, thereby reducing the background autofluorescence. Recently, researchers have focused on designing multimodal nanoparticles that will combine various functionalities, e.g., † Part of the “Larry Dalton Festschrift”. * To whom correspondence may be addressed. E-mail: pnprasad@ buffalo.edu. ‡ Institute for Lasers, Photonics and Biophotonics and Department of Electrical Engineering. § Department of Physics.
fluorescence, plasmonics, magnetism, and biotargetibility. Several methods, such as silica and polymer coating, have been used to engineer such multimodal nanoparticles.16–25 Silica-based nanoparticles have been widely used in biomedical applications because (i) they can facilitate stable aqueous dispersion of nonpolar substances, (ii) their surface can be easily functionalized with various functional groups that can be used for bioconjugation and target-specific delivery, and (iii) they are nontoxic and biocompatible. Effective encapsulation of QDs within a silica matrix also significantly reduces the possibility of environmental leakage of the constituent heavy atoms of the QDs, thus enhancing the overall biosafety profile of the resulting nanocomposites. Previously, our group has demonstrated the potential of organically modified silica (ORMOSIL) nanoparticles in various nanomedicinal approaches, such as photodynamic therapy (PDT) of cancer and gene delivery.16,17,26 These results show that ORMOSIL particles have provided a promising platform for life science-related research. Although doped silica nanoparticles with QDs and magnetite nanoparticles (Mag-NPs) have been produced by other methodologies, there has not been a reliable method of producing high-quality doped ORMOSIL particles with well-controlled size and maintained optical and magnetic properties.27–30 Recently, both Parak’s and Ying’s groups demonstrated the coencapsulation of QDs and Fe3O4 nanoparticles into silica particles for single-photon-excited cell imaging, without extending the capability of such particles for magnetically guided targeting cells.20,31,32 In this paper, we report the fabrication of ORMOSIL nanoparticles codoped with QDs and Mag-NPs, as a biocompatible and magnetically guided optical probe for two-photon imaging of live cancer cells. We present cell survivability results, which indicate the nontoxicity of these nanoparticles. In addition, we show that a combination of biotargeting and magnetic guidance can be used to synergistically enhance cellular uptake.
10.1021/jp712090y CCC: $40.75 2008 American Chemical Society Published on Web 04/25/2008
ORMOSIL Nanoprobes for Live Cancer Cell Imaging
J. Phys. Chem. C, Vol. 112, No. 21, 2008 7973
SCHEME 1: Synthesis of Coencapsulated ORMSIL Nanoparticles
Experimental Section Materials. Cadmium oxide, zinc acetate, sulfur, selenium, trioctylphosphine oxide (TOPO), trioctylphosphine (TOP), oleic acid, iron (III) acetylacetonate, 1,2-hexadecanediol, oleic acid, oleylamine, phenyl ether, butanol, triethoxyvinylsilane (VTES), 1-methyl-2-pyrrolidinone (NMP), and 3-aminopropyltriethoxysilane (APTES) were purchased from Aldrich. Pluronic F127 was obtained from BASF Corporation. 3-(4,5-Dimethylthiazol2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS assay reagent) was purchased from Promega. Synthesis of Iron Oxide (Fe3O4) Nanoparticles. Monodispersed (∼4 nm) Mag-NPs were synthesized according to the method reported by Sun et al.33 Briefly, the precursors, iron (III) acetylacetonate (2 nmol) and 1,2-hexadecanediol (10 mmol), oleic acid (6 mmol) and oleylamine (6 mmol) were
mixed with 20 mL of phenyl ether. The mixture was heated to 265 °C (509 °F) for 30 min. After 30 min, the mixture was cooled to room temperature. The nanoparticles were separated from the surfactant solution by the addition of ethanol and centrifugation. The dark-brown precipitate could be redispersed in various organic solvents, including hexane, toluene, and chloroform. Synthesis of CdSe/CdS/ZnS QDs. The bilayer-shell structured CdSe/CdS/ZnS QDs were synthesized by growing a CdS/ ZnS shell on the top of a CdSe core.34,35 A 0.4 g portion of the CdSe core was mixed with a Cd/Zn/S ratio of 1:3:4 (0.5 mmol of Cd, 1.5 mmol of Zn, and 2 mmol of S) in 10 mL of oleic acid. The total mixture was brought into reaction at ∼280 °C (536 °F). The QDs were separated from the surfactant solution by the addition of ethanol and centrifugation.
Figure 1. (a) TEM and (b) HRTEM images and (c) EDX analysis of nanoparticle-doped ORMOSIL nanoparticles.
7974 J. Phys. Chem. C, Vol. 112, No. 21, 2008
Law et al.
Figure 2. Pictures of the multifunctional ORMOSIL nanoparticles under the influence of an external magnetic force. The nanoparticles are observed to be pulled towards the “magnet side” of the vial, as seen under (a) normal and (b) UV light.
Figure 3. (a) Optical (absorbance and fluorescence) and (b) magnetic characterizations of QMd-SiO2 nanoparticles.
Figure 4. Photoluminescence propertiess(a) luminescence intensity and (b) emission spectrasof the QMd-SiO2 NPs under different pH conditions.
Synthesis and Characterization of Mag-NPs and QDCoencapsulated ORMOSIL Nanoparticles. The ORMOSIL nanoparticles were synthesized according to the procedures described by Roy et al., with slight modifications (Scheme 1).17 Typically, a micellar solution was prepared in advance by mixing 1% of Pluronic F127 (surfactant) and 0.4 mL of 1-butanol (cosurfactant) in 10 mL of double-distilled water
(HPLC grade). In a separate mixture solution, precalculated amounts of the ORMOSIL precursor triethoxyvinylsilane, ammonia, Mag-NPs, and QDs were well mixed with NMP. This mixture was then swiftly injected into the micellar solution under vigorous stirring. Amino-functionalized ORMOSIL nanoparticles could be obtained by the addition of APTES, which functionalized the surface of nanoparticle-doped ORMOSIL
ORMOSIL Nanoprobes for Live Cancer Cell Imaging
J. Phys. Chem. C, Vol. 112, No. 21, 2008 7975
Figure 5. Two-photon excited fluorescence microscopic images of Panc-1 cells treated with unmodified QMd-SiO2, (a) with and (b) without applied magnetic force. Left: transmission; middle: fluorescence; right: overlay.
Figure 6. Two-photon excited fluorescence microscopic images of Panc-1 cells treated with Tf-conjugated QMd-SiO2, (a) with and (b) without the presence of external magnetic field.
nanoparticles with terminated amino groups. The solution was left for stirring overnight, and then purified by dialysis against water for 24 h. Results and Discussion The nanoparticle-doped ORMOSIL particles were characterized by high-resolution transmission electron microscopy (HRTEM), energy dispersive X-ray spectroscopy (EDX), UV/vis, fluorescence spectroscopy, and a SQUID magnetometer. Figure 1 shows the TEM and HRTEM images of the doped ORMOSIL nanoparticles. Fe3O4 nanoparticles (∼4nm) and CdSe/CdS/ZnS QDs (∼5nm) were clearly observed in the ORMOSIL matrix. The actual size of the nanoparticle-doped ORMOSIL particles is estimated to be 30-40 nm. Further analysis of the doped ORMOSIL particles using EDX has confirmed the presence of Cd, Se, S, Si, and Fe. In this study, we refer to QD- and Mag-
NP-doped ORMOSIL nanoparticles as QMd-SiO2 NPs. Since the QMd-SiO2 NPs exhibit both luminescence and magnetic properties, they can be simply guided to a specific location by applying magnetic force on them. Figure 2 shows a photograph of the aqueous dispersion of QMd-SiO2 NPs under the influence of an external magnetic force. Upon placing a magnet bar at one side of the vial, it can be clearly seen that the QMd-SiO2 NPs were drawn to the “magnet side” of the vial. Upon illuminating the vial with UV light, an intense red color emission was observed on the “magnet side”, indicating that both the QDs and the Mag-NPs were successfully colocalized within the silica particles (QMd-SiO2 NPs). Figure 3a shows the UV absorption and photoluminescence (PL) spectra, in water, from the largely monodispersed QMdSiO2 NPs. The absorption spectrum features an excitonic peak around 610 nm, and the PL spectrum shows a band edge
7976 J. Phys. Chem. C, Vol. 112, No. 21, 2008
Law et al.
Figure 7. Cytotoxicity studies of Panc-1 cells treated with QMd-SiO2. MTS assays illustrating percentage cell viability (compared to nontreated cells being arbitrarily assigned 100% viability) upon exposing the cells to different concentrations of QMd-SiO2 and QMd-SiO2 -Tf for (a) 24 and (b) 48 h.
emission at ∼630 nm. Figure 3b shows the hysteresis loops of QMd-SiO2 NPs, which is measured at room temperature. The result indicates that the magnetic property was retained after encapsulating the Mag-NPs within the ORMOSIL matrix. The optical stability of the QMd-SiO2 NPs under varying conditions of pH was systematically investigated. Figure 4 shows the variation of PL intensity of the QMd-SiO2 NPs in acidicto-basic pH environments. From pH 6 to 12, the PL intensity varies by less than 15%, and also remains stable for more than 48 h. At pH 4, the PL intensity decreases by about 40% compared to that at neutral pH. On the other hand, at pH 2, ∼80% loss of their PL was observed immediately, and further degradation of the PL was observed after two days of storage at room temperature. However, it is worth mentioning that, for the QMd-SiO2 NPs dispersion in pH range of 2 to 12, the band edge emission of PL spectra was still maintained. The emission spectra are shown in figure 4b, and no spectral shift is observed over a wide range of pH values, indicating the robustness of the nanoparticles. To demonstrate the magnetically guided ability and the biocompatibility of these particles, two experiments were performed, (a) passive in Vitro targeting and (b) active targeting, with and without an applied magnetic force. Two-photon bioimaging technique was used to confirm the uptake of the QMd-SiO2 NPs in the pancreatic cancer cells line Panc-1. The day prior to experiment, an appropriate number of cells was seeded in 35 mm cell culture dishes. On the day of experiment, the cells (at 70-80% confluence) were incubated with the unmodified QMd-SiO2 NPs at a final concentration of 10 µg/ mL. The cells were incubated for 2 h with and without a bar magnet (0.5T, 20 mm diameter) placed underneath the culture dish, as illustrated in Figure 5. After 2 h of incubation, the culture dishes were washed with phosphate-buffered saline (PBS) to remove free QMd-SiO2 NPs, and directly imaged under a two-photon excited fluorescence microscope. Figure 5a shows two-photon excited fluorescence microscopic images of Panc-1 cells labeled with the QMd-SiO2 NPs under the influence of magnetic force. As shown in Figure 5a, the cells are labeled with the QMd-SiO2 NPs upon applying magnetic field gradient, which mostly accumulate on the cell surface. In comparison, Figure 5b, the control dish without applied magnetic force, shows minimal uptake of the QMdSiO2 NPs. These results strongly support the idea that, by simply manipulating the magnetic field gradient, one could improve
the uptake of the QMd-SiO2 NPs by the cancer cells. Since the excitation wavelength used in two-photon microscopy is 884 nm (doubling the wavelength of UV light), this technique should enable long-term monitoring of cellular activities with minimal background autofluorescence and reduced photodamage. In addition to magnetic targeting alone, we have explored the potential synergy between magnetic targeting and receptormediated targeting on the overall in Vitro cellular uptake of these nanoparticles. In order to achieve that, we have conjugated QMd-SiO2 NPs terminated with amino groups with the tumor targeting molecule transferrin (Tf), whose corresponding receptors (TfRs) are well-known to be overexpressed on many types of cancer, including pancreatic cancer.14,36 In our experiment, the Tf-conjugated QMd-SiO2 NPs were treated with Panc-1 cells in culture dishes at a final concentration of 2.5 µg/ml, with and without a bar magnet placed underneath. After 2 h of incubation, the culture dish was washed with PBS and directly observed in a confocal microscope under two-photon excitation. Figure 6a shows the images of Panc-1 cells labeled with QMd-SiO2 NP-Tf bioconjugates under the influence of magnetic force. Upon comparing with the image shown in Figure 4a, where unconjugated QMd-SiO2 NPs were used for cell treatment under the same conditions, a significant improvement of cell labeling was observed. On the other hand, the cellular uptake of the QMd-SiO2 NP-Tf bioconjugates without the presence of magnetic force is found to be much weaker (Figure 6b). This experiment illustrates that synergistic interaction with two kinds of in Vitro targeting modes results in robust intracellular uptake (Figure 6a), which is much stronger compared to that obtained using individual targeting mode (e.g., Figure 4a with magnetic targeting only and Figure 6b with receptor-mediated targeting only). Also, it can be observed from Figure 6a that the QMdSiO2 NP-Tf bioconjugates appeared to accumulate in vesicles within the cells, which again indicates the transferrin receptor (TfR)-mediated endocytotic uptake. In addition, from Figures 4 to 6, one can observe no sign of morphological damage of cells, suggesting that the QMd-SiO2 NPs can perform as robust in Vitro optical probes at nontoxic dosages. The in Vitro cytotoxicity of the QMd-SiO2 NPs was evaluated using a colorimetric cell-viability (MTS) assay. For MTS assay studies, 30 culture wells (six sets, each set contains five wells) containing Panc-1 cells were used.37 Five sets were treated with five different QMd-SiO2 NPs (or QMd-SiO2 NP-Tf) concentrations (2.5, 5, 10, 15, and 20 µg/ml) and the last set was used as
ORMOSIL Nanoprobes for Live Cancer Cell Imaging the untreated control. Each experiment was repeated five times. Figure 7 shows the in Vitro cytotoxicity effects of QMd-SiO2 NPs on the Panc-1 cell line. It was observed that QMd-SiO2 NPs maintained greater than 80% cell viability even at particle loadings as high as ∼20 µg/mL. The low cytotoxicity of QMdSiO2 NPs can be attributed to the effective protection of QDs and Mag-NPs by the silica coating. The preceding studies not only demonstrate the biocompatibility and robustness of the QMd-SiO2 NPs, but also highlight their potential to serve as a magnetically guided biomarker for in ViVo imaging and drug tracking. In this study, the overall size of the QMd-SiO2 NPs was controlled using Pluronic F127 as the surfactant. To date, it is generally known that the type of surfactant plays a crucial role in determining the final shape and the size of the nanoparticles as well as their colloidal stability. Pluronic F127 (a.k.a. Poloxamer 407) has been extensively used for diverse pharmaceutical applications, both in Vitro and in ViVo.38,39 Therefore, the QMd-SiO2 NPs passivated with Pluronic F127 offers a very promising platform for future in ViVo studies. Conclusion In conclusion, we have prepared QMd-SiO2 NPs using a micellar reverse-phase synthesis method. The QMd-SiO2 NPs were magnetically guided by an external magnetic force to specifically target pancreatic cancer cells, which was confirmed by using two-photon bioimaging technique. The Tf-conjugated QMd-SiO2 NPs were found to have a significantly higher uptake in the cancer cells than that obtained using unconjugated QMdSiO2 NPs under the influence of external magnetic field. The use of Pluronic F127 as the capping agent, with the observed low cytotoxicity, the spectral robustness of the QMd-SiO2 NPs, and the potential extension of this method for encapsulating noncadmium-based QDs (e.g., indium phosphide, silicon) as well, allows for the provision of extending these multifunctional nanoparticles to in ViVo bioimaging studies. Acknowledgment. This study was supported by grants from the NCI RO1CA119397, R01CA104492, the John R. Oishei Foundation, and the Chemistry and Life Sciences Division of the Air Force Office of Scientific Research and the University at Buffalo Interdisciplinary Research and Creative Activities Fund. References and Notes (1) Prasad, P. N. Nanophotonics; Wiley-Interscience: New York, 2004. (2) Prasad, P. N. Introduction to Biophotonics; Wiley-Interscience: New York, 2004. (3) Bruchez, M, Jr.; Moronne, M.; Gin, P.; Weiss, S.; Alivisatos, A. P. Science 1998, 281, 2013–2016. (4) Chan, W. C. W.; Nie, S. Science 1998, 281, 2016–2018. (5) Bharali, D. J.; Lucey, D. W.; Jayakumar, H.; Pudavar, H. E.; Prasad, P. N. J. Am. Chem. Soc. 2005, 127, 11364–11371. (6) Qian, J.; Yong, K. T.; Roy, I.; Ohulchanskyy, T. Y.; Bergey, E. J.; Lee, H. H.; Tramposch, K. M.; He, S.; Maitra, A.; Prasad, P. N. J. Phys. Chem. B 2007, 111, 6969–6972. (7) Jayagopal, A.; Russ, P. K.; Haselton, F. R. Bioconjugate Chem. 2007, 18, 1424–1433.
J. Phys. Chem. C, Vol. 112, No. 21, 2008 7977 (8) Kim, I. B.; Shin, H.; Garcia, A. J.; Bunz, U. H. F. Bioconjugate Chem. 2007, 18, 815–820. (9) Hyun, B. R.; Chen, H. Y.; Rey, D. A.; Wise, F. W.; Batt, C. A. J. Phys. Chem. B 2007, 111, 5726–5730. (10) Wang, H.-Q.; Zhang, H.-L.; Li, X.-Q.; Wang, J.-H.; Huang, Z.-L.; Zhao, Y.-D. J. Biomed. Mater. Res., Part A 2007, DOI: 10.1002/jbm.a.31682 (11) Klostranec, J. M. ; Chan, W. C. W. AdV. Mater. 2006, 18, 1953– 1964. (12) Xing, Y.; Chaudry, Q.; Shen, C.; Kong, K. Y.; Zhau, H. E.; Chung, L. W.; Petros, J. A.; O’Regan, R. M.; Yezhelyev, M. V.; Simons, J. W.; Wang, M. D.; Nie, S. Nat. Protocols 2007, 2, 1152–1165. (13) Fu, A.; Gu, W.; Boussert, B.; Koski, K.; Gerion, D.; Manna, L.; LeGros, M.; Larabell, C. A.; Alivisatos, A. P. Nano Lett. 2007, 7, 179– 182. (14) Yong, K. T.; Qian, J.; Roy, I.; Lee, H. H.; Bergey, E. J.; Tramposch, K. M.; He, S.; Swihart, M. T.; Maitra, A.; Prasad, P. N. Nano Lett. 2007, 7, 761–765. (15) Gao, D.; Agayan, R. R.; Xu, H.; Philbert, M. A.; Kopelman, R. Nano Lett. 2006, 6, 2383–2386. (16) Ohulchanskyy, T. Y.; Roy, I.; Goswami, L. N.; Chen, Y.; Bergey, E. J.; Pandey, R. K.; Oseroff, A. R.; Prasad, P. N. Nano Lett. 2007, 7, 2835–2842. (17) Roy, I.; Ohulchanskyy, T. Y.; Bharali, D. J.; Pudavar, H. E.; Mistretta, R. A.; Kaur, N.; Prasad, P. N. Proc. Natl. Acad. Sci. U.S.A. 2005, 102, 279–284. (18) Salgueirin˜o-Maceira, V.; Correa-Duarte, M. A.; Spasova, M.; LizMarza´n, L. M.; Farle, M. AdV. Funct. Mater. 2006, 16, 1266. (19) Tan, W. B.; Zhang, Y. AdV. Mater. 2005, 17, 2375–2380. (20) Yi, D. K.; Selvan, S. T.; Lee, S. S.; Papaefthymiou, G. C.; Kundaliya, D.; Ying, J. Y. J. Am. Chem. Soc. 2005, 127, 4990–4991. (21) Zhang, T.; Stilwell, J. L.; Gerion, D.; Ding, L.; Elboudwarej, O.; Cooke, P. A.; Gray, J. W.; Alivisatos, A. P.; Chen, F. F. Nano Lett. 2006, 6, 800–808. (22) Sukhorukov, G. B.; Rogach, A. L.; Garstka, M.; Springer, S.; Parak, W. J.; MuC¸oz-Javier, A.; Kreft, O.; Skirtach, A. G.; Susha, A. S.; Ramaye, Y.; Palankar, R.; Winterhalter, M. Small 2007, 3, 944–955. (23) Yu, W. W.; Chang, E.; Falkner, J. C.; Zhang, J.; Al-Somali, A. M.; Sayes, C. M.; Johns, J.; Drezek, R.; Colvin, V. L. J. Am. Chem. Soc. 2007, 129, 2871–2879. (24) Yang, H.; Holloway, P. H.; Santra, S. J. Chem. Phys. 2004, 121, 7421–7426. (25) Koo, Y.-E. L.; Reddy, G. R.; Bhojani, M.; Schneider, R.; Philbert, M. A.; Rehemtulla, A.; Ross, B. D.; Kopelman, R. AdV. Drug DeliVery ReV. 2006, 58, 1556–1577. (26) Roy, I.; Ohulchanskyy, T. Y.; Pudavar, H. E.; Bergey, E. J.; Oseroff, A. R.; Morgan, J.; Dougherty, T. J.; Prasad, P. N. J. Am. Chem. Soc. 2003, 125, 7860–7865. (27) Wang, D.; He, J.; Rosenzweig, N.; Rosenzweig, Z. Nano Lett. 2004, 4, 409–413. (28) Sathe, T. R.; Agrawal, A.; Nie, S. Anal. Chem. 2006, 78, 5627– 5632. (29) Mulder, W. J. M.; Koole, R.; Brandwijk, R. J.; Storm, G.; Chin, P. T. K.; Strijkers, G. J.; de Mello Donega, C.; Nicolay, K.; Griffioen, A. W. Nano Lett. 2006, 6, 1–6. (30) Sahoo, Y.; Poddar, P.; Srikanth, H.; Lucey, D. W.; Prasad, P. N. J. Phys. Chem. B 2005, 109, 15221–15225. (31) Selvan, S. T.; Patra, P. K.; Ang, C. Y.; Ying, J. Y. Angew. Chem., Int. Ed. 2007, 46, 2448–2452. (32) Zebli, B.; Susha, A. S.; Sukhorukov, G. B.; Rogach, A. L.; Parak, W. J. Langmuir 2005, 21, 4262–4265. (33) Sun, S.; Zeng, H. J. Am. Chem. Soc. 2002, 124, 8204–8205. (34) Manna, L.; Scher, E. C.; Li, L. S.; Alivisatos, A. P. J. Am. Chem. Soc. 2002, 124, 7136–7145. (35) Qu, L.; Yu, W. W.; Peng, X. Nano Lett. 2004, 4, 465–469. (36) Jiang, W.; Mardyani, S.; Fischer, H.; Chan, C. W. Chem. Mater. 2006, 18, 872–878. (37) Ding, H.; Yong, K. T.; Roy, I.; Pudavar, H. E.; Law, W. C.; Bergey, E. J.; Prasad, P. N. J. Phys. Chem. C 2007, 111, 12552–12557. (38) El-Kamel, A. H. Int. J. Pharm. 2002, 241, 47–55. (39) Dumortier, G.; Grossiord, J. L.; Agnely, F.; Chaumeil, J. C. Pharm. Res. 2006, 23, 2709–2728.
JP712090Y
