Characterization and Bacterial Response of Zinc Oxide Particles

Apr 3, 2009 - On the basis of their good PL and biocompatible properties, the ... Approximately 10 mg of the powder was placed into an alumina .... an...
0 downloads 0 Views 2MB Size
Download PDF
J. Phys. Chem. B 2009, 113, 6047–6053

6047

Characterization and Bacterial Response of Zinc Oxide Particles Prepared by a Biomineralization Process Danhong Yan,† Guangfu Yin,† Zhongbing Huang,*,† Mei Yang,† Xiaoming Liao,† Yunqing Kang,† Yadong Yao,† Baoqing Hao,*,‡ and Dong Han§ College of Materials Sciences and Engineering, Sichuan UniVersity, No. 24, South First Section, First Ring Road, Chengdu, Sichuan, 610065 People’s Republic of China, College of Life Science & Technology, Southwest UniVersity for Nationalities, No.16, South Fourth Section, First Ring Road, Chengdu, People’s Republic of China, and Zhengzhou Research Institute, Aluminum Corporation of China Limited ReceiVed: October 6, 2008; ReVised Manuscript ReceiVed: December 9, 2008

In this paper, olive-like ZnO particles were successfully synthesized via a facile biomineralization process in the template of silk fibroin (SF) peptide at room temperature. The coat of SF peptide on the surface of ZnO particles had a substantial influence on their morphology during the biomineralization. Room-temperature photoluminescence behavior of ZnO particles indicated that the visible blue emission peak centered at 410 nm was enhanced with the mineralization time. Bacteriological tests revealed that the mineralized ZnO particles with SF peptide were not toxic for Staphylococcus aureus, Escherichia coli, and Streptococcus agalactiae, presenting good cytocompatibility due to the surface coat of peptide. Their potential applications in biooptical detectors could be envisioned. Introduction In recent years, a mild room-temperature aqueous mineralization process has been developed. This process required mild reaction conditions under atmospheric pressure, mimicking the natural biomineralization process conditions.1 It uses organic templates as the structure-directing agent to control the nucleation and subsequent crystal growth and eventually to yield a unique crystal structure.2 The group of Coffer first proposed application of a calf thymus DNA template in the biomineralization of CdS nanoparticles.3 Liang et al. prepared CdS nanorods by using self-assembled DNA-membrane complexes as a template.4 Banfield reported the biomineralization of β-FeOOH using kainic acid.5 With the development of biotechnology, self-aggregation or -assembly of artificial peptides with an affinity for nonbiological inorganic materials was utilized for promoting crystal growth during the biomineralization process.6,7 Falini reported the oriented crystallization of calcite, aragonite, and vaterite by means of cross-linked collagenous matrixes with entrapped poly-L-aspartate (poly-Asp) or polyL-glutamate (poly-Glu).8 Many micro- or nanostructured materials have been successfully synthesized by this technique.9-14 These mineralized 3-D structure materials possess a high surface-to-volume ratio and absorbing properties. Nanostructured ZnO materials have attracted significant attention due to their interesting unique properties and novel potential applications, such as blue-light-emitting diodes (LEDs),15 gas sensors,16 and ultraviolet nanolasers,17 and due to their large direct energy band gap of 3.37 eV at room temperature, a large exciton binding energy of 60 meV, and an excitonic emission in the ultraviolet region.18 The diverse performance of applications requires the fabrication of mor* To whom correspondence should be addressed. Tel/Fax: 86-2885413003. E-mail: [email protected]. (Z.H.); Tel/Fax: 86-28-86714164. E-mail: [email protected] (B.H.). † Sichuan University. ‡ Southwest University for Nationalities. § Aluminum Corporation of China Limited.

phologically and functionally distinct ZnO nanostructures. Up until now, a variety of ZnO nanostructures such as nanowires,19,20 nanorods,21,22 nanobelts,23,24 nanoflowers,25 and nanospheres26 have been reported. Among the various methods of ZnO synthesis, the technique of synthesizing ZnO at room temperature is attracting a growing interest. ZnO nanoparticles are believed to be nontoxic and biocompatible27 and have been used in many applications in daily life, such as drug carriers and cosmetics and fillings in medical materials.28,29 However, some experts have observed its toxicological effect on target microorganisms.30,31 Therefore, it is of great significance to produce nontoxic and biocompatible ZnO nanomaterials. It was reported that an artificial peptide with an affinity for ZnO was applied as a template to synthesize ZnO nanoparticles via the biomineralization strategy.32 However, these artificial peptides for ZnO biomineralization were expensive and scarce, and the cytocompatibility of the biomineralized ZnO product have not reported up to now. As known to all, silk fibroin (SF) is one of the most extensive biomaterials because of its good biocompatibility, and it can be hydrolyzed into a peptide, providing nucleophilic hydroxyl groups of amino acids, which are very important in the nucleation process of biomineralization. In this paper, we demonstrate a mild room-temperature aqueous solution mineralization process to prepare the uniform olive-like ZnO particles using SF peptide as a template, and their photoluminescence (PL) properties are investigated. Bacteriological tests were performed on Staphylococcus aureus, Escherichia coli, and Streptococcus agalactiae in order to determine their toxicity. Due to SF peptide coating, the mineralized ZnO particles displayed no toxicity to these bacteria and presented good biocompatibility. On the basis of their good PL and biocompatible properties, the biomineralized ZnO particles for biodevice applications would be envisioned.

10.1021/jp808805w CCC: $40.75  2009 American Chemical Society Published on Web 04/03/2009

6048 J. Phys. Chem. B, Vol. 113, No. 17, 2009

Yan et al.

TABLE 1: Amino acid Composition of Silk Fibroin of Bombyx mori37 amino acid

Asp

Thr

Ser

Glu

Gly

Ala

Val

Tyr

percentum (mol%)

4.43 1.61 12.51 1.13 39.42 34.92 1.11 0.41

amino acid

Ile

Leu

Phe

Lys

His

Arg

Pro

percentum (mol%)

0.07

0.18

0.08

0.79

0.17

0.90

0.26

Experimental Procedures B. mori silk fiber was boiled for 30 min in 0.3% Na2CO3 solution to degum the glue-like sericin coating. After dried, silk fibroin was hydrolyzed in 6 M HCl at 80 °C for a series of hours. The SF-hydrolyzed solution was adjusted to pH 7 and dialyzed with distilled water for about 24 h at 4 °C. The 0.1 M zinc nitrate solution was mixed with the same volume of 0.2 M hydrate of sodium. The produced Zn(OH)2 was rinsed several times with distilled water, and then, the final concentration of Zn(OH)2 was 0.1 M. A 2 mL solution of SFhydrolyzed solution (0.1 mg/ml) was added to 40 mL of Zn(OH)2(sol) solution, and the solution was incubated at room temperature. When precipitated particles were observed, they were rinsed with distilled water to remove residual Zn(OH)2(sol) and then dried at room temperature for 24 h. The morphology of the ZnO particles was obtained by scanning electron microscopy (SEM, JSM-5900LV, Japan). The crystal structure of the samples was characterized by highresolution transmission electronic microscopy (HRTEM, Philips TECNAI 20 high-resolution TEM at 400 kV) and X-ray diffraction (XRD, X’Pert, Holand) with Cu KR radiation. Fourier transform infrared (FT-IR) spectra were recorded by an IRPrestige-21 spectrometer. Optical properties were investigated by photoluminescence measurement (F-7000, Hitachi) with a Xe lamp (310 nm in wavelength) as the excitation light source at room temperature. Synchronization of differential thermal analysis (DTA) and thermogravimetry (TG) were carried out with a TG/SDTA851e analyzer of METTLER-TOLEDO Co.

(Switzerland). Approximately 10 mg of the powder was placed into an alumina vessel and heated at a rate of 5 °C min-1 up to 320 °C in air. Antibacterial tests were performed by measuring the growth number of colonies on solid agar plates with different concentrations of ZnO fluids (from 0.3 to 0.003 M). In order to obtain ZnO fluids for the antibacterial tests, a preset amount of dry ZnO particles was mixed with distilled water in a glass beaker with the aid of a magnetic stirrer. Once particles were dispersed in water, the beaker was placed in an ultransoicator (AS72040A, Autosicience Instrument Co. Ltd., Tianjin, China) for 30 min in order to avoid the agglomerates of ZnO particles. Three strains of S. aureus, E. coli, and S. agalactiae were kindly supplied by Cell-biology Laboratory of Southwest University for Nationalities (China). Bacteria strains were cultivated in LB medium (pH 7.2) containing 5 g/L of yeast extract, 10 g/L of tryptone, and 10 g/L of NaCl in a shaking incubator at 180 rpm and 37 °C overnight until the cell counts reached a minimum of 107 CFU/ mL. Bacteria cultures were further diluted to obtain a final inocula of ∼103 CFU/mL. In a typical experiment, 50 µL of the bacteria culture and 200 µL of autoclaved ZnO fluids were coated by a glass spatula on the surface of solid agar plates. Agar plates without ZnO were established as controls. The plates were incubated at 37 °C, and colony counts were taken after 24 h of incubation. All experiments were conducted in triplicate for each strain. TEM analyses of bacteria thin sections were used to study the biocidal effect of ZnO NPs. Results and Discussion In this study, SF peptide was utilized as a template to promote crystal growth. Silk is spun by the B. mori and mainly consists of two major proteins, SF, the major structural protein, and sericin, the glue-like protein.34 The sericin protein coating of silkworm fibers are reported to stimulate an immune response.35 SF, which can be obtained by removing the outer sericin of silk fiber in the sodium carbonate solution, is one of the most extensively studied biomaterials because of its good biodegradability and biocompatibility.36 SF is made up of two polypeptide

Figure 1. SEM images of ZnO particles biomineralized in different SF peptide templates; SF hydrolyzed in 6 M HCl at 80 °C for (a) 4, (b) 8, (c) 10, and (d) 12 h.

Characterization and Bacterial Response of Zinc Oxide

J. Phys. Chem. B, Vol. 113, No. 17, 2009 6049

Figure 2. SEM images of ZnO grown at different mineralization times; (a) 6 h, (b) 12 h, (c) 2 days, (d) 7 days, (e) 14 days, (f) 21 days, and (g) 28 days.

chains linked by a disulfide bridge. The larger heavy chain (391 kDa) is comprised of 12 low-complexity “crystalline” domains made up of Gly-X repeats and covering 94% of the sequence; X is Ala in 64%, Ser in 22%, Tyr in 10%, Val in 3%, and Thr in 1.3% of the repeats. Each crystalline domain is made up of subdomains of ∼70 residues, which, in most cases, begin with repeats of the GAGAGS hexapeptide and terminate with the GAAS tetrapeptide.37-39 The detailed amino acid composition of silk fibroin of B. mori is presented in Table 1. In order to investigate the effect of SF peptide on the morphology of ZnO particles, SF protein hydrolyzed for 4 (peptide 1#), 8 (peptide 2#), 10 (peptide 3#) and 12 h (peptide 4#) were used as templates. Different molecular chains of SF peptide were obtained by different hydrolysis times, and the molecular chains were shortened with the increase of hydrolysis time in 6 M HCl.40 SEM images in Figure 1 show the heterogeneous morphology of ZnO particles obtained using SF peptides 1#-4# as the

templates. Figure 1a shows many globe-like particles with diameters of 1.0-3.0 µm in the template of peptide 1#, and each one is composed of small particles with diameters of 0.1-0.5 µm. ZnO particles in the presence of peptide 2# are mineralized to form hexagonal platelets with diameters of ∼1 µm and thicknesses of ∼100 nm (shown in Figure 1b). In Figure 1c, not only ZnO platelets with a size of ∼1 µm but also olive-like particles with diameters of ∼0.2 µm were observed in the template of peptide 3#. Figure 1d obviously shows uniform olivelike particles with ∼0.2 µm diameters and ∼0.5 µm lengths. The results of these SEM images indicated that SF peptide chains had a substantial influence on ZnO particle morphology during the mineralization process. Obviously, the shorter peptide molecular chains tended to yield smaller particles (shown in Figure 1d). In this paper, SF peptide 4# was chosen as a template in following work.

6050 J. Phys. Chem. B, Vol. 113, No. 17, 2009

Figure 3. XRD patterns of ZnO grown with different mineralization times.

On the basis of the above results, we have known that peptides present important an influence on the morphology of ZnO particles during the mineralization process. The special effects of peptides have been investigated by Peter et al.41 The Pro, Cit, and Gly-Gln of peptide chains could absorb Zn(OH)2 and yield a zincite crystal nucleus. 41 His or Gly-His can inhibit the formation of larger crystals and stabilize nanoparticles. As mentioned above, SF peptide as a template includes abundant Gly-X repeats (X is Ala, Ser, Tyr, Val, and Thr). In addition, because of their special primary structure and many charged amino acids, the SF peptides could allow electrostatic absorption of positively and negatively charged molecules and nanoparticles. Electrostatic absorption is very important in the nucleation process, in which amphiphile amino acid residues of SF peptide are able to capture cationic Zn2+ and anionic OH-. Zn2+ in Zn(OH)2(sol) tends to associate with the amphiphile zones of the peptide; then, they aggregate together, and Zn(OH)2 further condenses into ZnO particles through a biochemical process. The SEM images in Figure 2 show different ZnO morphologies in the presence of peptide 4# for different mineralization times. Figure 2a shows that ZnO particles after 6 h of growth are about 100 nm, suggesting that Zn(OH)2 has been biomineralized into ZnO particles in the template of SF peptide. After 12 h, the remarkable change of the ZnO morphology occurred. The particles grew bigger and tended to form an olive-like shape with a diameter of about 0.5 µm (shown in Figure 2b). After 2 days, the SEM image (Figure 2c) shows an olive-like anisotropic growth with diameters of 0.8-1 µm. In Figure 2, ZnO particles in the short growth time are much smoother than those in the long growth time. Compared with samples obtained in the short time (6 h-14 days), ZnO particles obtained in 28 d (shown in Figure 3g) include some fine particles accreted on the olive’s

Yan et al. surface. During the mineralization process, the nucleation occurred in the template of the SF peptide; subsequently, abundant amounts of Zn(OH)2 were transformed into ZnO crystals, and a lot of hollow structures also occurred along with the formation of ZnO, which resulted in the rough surfaces of ZnO particles. In addition, the size of ZnO particles was increased with the mineralization time. However, SEM results indicate that ZnO particles are rather uniform in size from 2 to 28 days. A distinct change of morphology in 12 h indicates that the nucleation and major crystal growth processes should happen in this period. Figure 3 shows XRD patterns of ZnO particles at different mineralization times. For all samples, their diffraction peaks can be well indexed as the pure ZnO zincite structure. Compared with the standard diffraction patterns (JCPDS Card File 361454), no characteristic peaks from other phases were detected. The intensity of ZnO particles of 14 days of mineralization is stronger than that of 7 days and 2 days of mineralization time. Moreover, the ZnO particles of 28 days possess the strongest intensity in all samples. The enhanced intensity of their diffraction patterns indicates that the crystallite sizes in ZnO particles are increased with the increase of mineralization time. In addition, the strongest peaks of their diffraction patterns are (002) ones, suggesting that the preferred growth orientation of these samples is the c-axis. The HRTEM image in Figure 4a shows a segment from the top of a typical olive-like ZnO particle. Only the fringes of the (002) planes with a lattice space of about 2.8 Å can be clearly observed, indicating that the mineralized ZnO particles have a good crystal structure. It further confirms that the growth orientation is along the (002) direction, which is consistent with the result of XRD pattern (shown in Figure 3). In addition, the ZnO particle is covered with an amorphous thin layer of peptide coating (marked by the black arrow in Figure 4a). The hydrophilic outer shell of the peptide could enhance the cellular absorption on the surface of ZnO particles. Figure 5 illustrates the FT-IR absorption spectrum of a mineralized ZnO sample. A peak at 3428 cm-1 is the stretching vibration of the H-O bond. Two peaks at 1620 and 1390 cm-1 are assigned to the vibrations of amide I and amide II, respectively. The peak of the phenyl group of phenylalanine centers at ∼865 cm-1. A peak at ∼480 cm-1 is the stretching vibration of the Zn-O bond in ZnO particles. Furthermore, the vibration of the Zn-O bond is interfered with by the SF peptide coating of ZnO particles, leading to the distinct peak of ∼413 cm-1. Figure 6 shows the PL intensity of the biomineralized ZnO particles at different growth times. Three peaks located at about 410, 470, and 530 nm could be observed. ZnO particles of long

Figure 4. (a) HRTEM image of a segment from the top of a ZnO particle corresponding to the rectangle region of (b) a typical olive-like ZnO particles; a black arrow points out the amorphous thin layer on the ZnO particles.

Characterization and Bacterial Response of Zinc Oxide

J. Phys. Chem. B, Vol. 113, No. 17, 2009 6051

Figure 5. FT-IR absorption spectrum of mineralized ZnO particles.

Figure 6. Room-temperature PL spectra of biomineralized ZnO particles at different times.

growth time have a stronger luminescence intensity than that of the short growth time. Furthermore, the increase of the luminescence intensity is proportional to the increase of mineralization time. The enhanced luminescence intensity of ZnO particles indicates that the crystallite size in ZnO particles was increased with the mineralization time. An obvious green band at ∼530 nm appears in the PL spectra of ZnO particles in the shorter growth time (6 and 12 h), suggesting that the green band emission corresponds to the singly ionized oxygen vacancy in these ZnO particles.42,43 Namely, a very high concentration of oxygen vacancy in ZnO particles was generated using the biomineralization method. However, the oxygen vacancy decreases with the mineralization time, suggesting that the integrity and crystallization of ZnO particles was increased with the mineralization time. In order to examine the toxicity of biomineralized ZnO particles, bacteriological tests were performed on S. agalactiae, S. aureus, and E. coli. The biocidal effect of biomineralized samples (with size of about 100 nm obtained in 6 h) on these three bacteria are presented in Figure 7. The initial cell counts for these three experimental runs were about 200 CFU per plate. The concentration of ZnO particles was varied from 0.3 to 0.003 M. A ZnO suspension of the concentration between 0.3 and 0.038 M could inhibit bacterial growth of 30-50% for S. agalactiae. For a ZnO suspension of 0.019 M concentration, a slight increase in the amount of S. agalactiae colonies was detected. Besides, the S. agalactiae colony amount increases with the decrease of the concentration of the ZnO suspension. The concentration of 0.3 M could inhibit E. coli and S. aureus growth of 25%. With the decrease of concentration of the ZnO

Figure 7. Means and standard errors of CFU per plate of (a) S. agalactiae, (b) E. coli, and (c) S. aureus incubated in LB media in the presence of different concentrations of ZnO particles for 24 h; the experiments were performed in triplicate.

suspension, a remarkable promoting effect on the growth of E. coli and S. aureus was detected. Especially with concentrations of 0.019 and 0.009 M, the colony amount is several times that of the control group. We have reported in previous work that ZnO particles prepared by the chemical method have antibacterial properties.33 Compared with them, the biomineralized ZnO particles with the thin coating layer of SF peptide possess a remarkable nontoxicity to these bacteria, suggesting that the biomineralized samples have good cytocompatibility. TEM images of bacterial ultrathin sections allow direct visualization of morphology changes of cells after contact with the mineralized ZnO NPs. S. agalactiae and S. aureus are two kinds of Gram-positive cocci. Figure 8a and c shows that the mineralized NPs (marked by black arrows) penetrated the cell membrane and were internalized inside of S. agalactiae and S.

6052 J. Phys. Chem. B, Vol. 113, No. 17, 2009

Yan et al.

Figure 8. TEM images of bacteria thin sections with biomineralized sample (0.003 M) internalization; (a) Streptococcus agalactiae, (b) Escherichia coli, and (c) Staphylococcus aureu, in which the NP is ZnO.

as an oligoelement,44 which results in the biomineralized ZnO particles being nontoxic for three bacteria. In this study, cell permeability significantly increases at the certain concentration of ZnO. Obviously, the coating of SF peptide not only could permit the mineralized particle to penetrate through the cell wall, which is not damaged, but could also promote bacterial growth by metabolization. We can also predict through their good PL and cytotoxic properties that the biomineralized ZnO particles would be used in the preparation of biodevices or the biodegradable fillings in vivo. Conclusion Figure 9. TG/DTG curves of the sample obtained in 28 days.

aureus. Furthermore, the cell membranes remained integral, cell euchromatins dispersed homogenously inside of cytoplasm, and no intracellular vacuole was observed. E.coli is a moderate Gram-negative bacillus that presents a tubular form. The E. coli cell wall is composed of an organized triple membrane, including a thin inner layer of peptidoglycan between an outer membrane including porins, phospholipid molecules, lipopolysaccharides, lipoproteins, and surface proteins and a cytoplasmic membrane including phospholipids molecules and porins. E. coli results in a ZnO-LB agar medium that also shows that the cell walls are not obviously damaged. The biomineralized NPs inside of the cells can be clearly observed (shown in Figure 8b). The cell walls of E. coli are integral, and the intracellular content does not leak out. All of these results indicate that the biomineralized ZnO NPs have no cytotoxicity on both Grampositive and Gram-negative cells, which is not consistent with the previous results of ZnO NPs prepared by the chemical method.33,44 Obviously, the SF peptide coated on the surface of ZnO NPs plays an important role in the promotion of bacteria growth. TG was carried out to determine the content of SF peptide in ZnO particles. Figure 9 shows the TG/DTG curve of the ZnO sample obtained in 28 days. Moderate weight loss for the ZnO particles up to 100 °C is attributed to the release of adsorbing water on the surface. The exothermic events with weight loss of about 4% at ∼170 °C result from the thermal decomposition of the SF peptide. In terms of cell compatibility, SF is arguably well-suited for cell culture purposes. Chiarini45 and Minoura46 both reported that the coating layers of SF result in better cell adherence and consequently greater proliferation of fibroblasts in comparison to the layers without SF. In this report, the bacteriological effect of the SF peptide-coated ZnO particles on S. agalactiae, S. aureus, and E. coli shows a remarkable bacterial promotion in certain concentrations. Maybe one could believe through these results that these increases are metabolismdependent because bacteria can metabolize SF peptide and Zn2+

Olive-like ZnO particles have been successfully prepared by the biomineralization process with the assistance of SF peptide at room temperature. SF peptides as the template induce the heterogeneous nucleation of ZnO and substantially influence the morphology of the mineralized ZnO particles. Bacterial experiments indicated that mineralized ZnO particles with certain concentrations remarkably promote the growth of bacteria. Compared with ZnO particles prepared by a chemical method, the mineralized ZnO particles possess no toxicity to bacteria, indicating favorable cytocompatibility due to the SF peptide coating on the mineralized ZnO particles. On the basis of the noncytotoxic and good PL properties of the biomineralized material, a potential application of bio-optical detectors could be envisioned. Acknowledgment. This work has been supported by the National Natural Science Foundation of China (Project No. 60871062 and 50873066). The support of Sichuan Province through a Science Fund for Distinguished Young Scholars of Sichuan Province (08ZQ026-007 and 07ZQ026-118) and Key Technologies Research and Development Program of Sichuan Province (2008SZ0021 and 2006Z08-001-1) are also acknowledged with gratitude. This work was also supported by the Research Fund for the Doctoral Program of Higher Education from Ministry of Education of China (No. 20070610131). We thank the Analytical & Testing Center, Sichuan University, for assistance with the microscopy work. References and Notes (1) Xia, Y.; Yang, P.; Sun, Y.; Wu, Y.; Mayers, B.; Gates, B.; Yin, Y.; Kim, F.; Yan, H. AdV. Mater. 2003, 15, 353. (2) Mann, S. Biomineralization: Principle and Concepts in Bioinorganic Materials Chemistry; Oxford University Press: Oxford, 2001. (3) Coffer, J. L.; Russell, F. P.; Li, X.; Yong, G. R.; Chen, Y. D.; Robert, M. P.; Irma, L. P. AdVances in Microcrystalline and Nanocrystalline Semiconductor, Materials Research Society Symposium, San Francisco, CA, March 31–April 4, 1997. (4) Liang, H. J.; Angelini, T. E.; Braun, P. V.; Wong, G. C. L. J. Am. Chem. Soc. 2004, 126, 14157. (5) Banfield, J. F.; Chan, C. S.; Stasio, G. D.; Welch, S. A.; Girasole, M.; Frazer, B. H.; Nesterova, M. V.; Fakra, S. Science 2004, 303, 1656.

Characterization and Bacterial Response of Zinc Oxide (6) Whaley, S. R.; English, D. S.; Hu, E. L.; Barbara, P. F.; Belcher, A. M. Nature (London) 2000, 405, 665. (7) Sarikaya, M.; Tamerler, C.; Jen, A.K.-Y.; Schulten, K.; Baneyx, F. Nat. Mater. 2003, 2, 577. (8) Falini, G. Int. J. Inorg. Mater 2000, 2, 455. (9) Yu, S. H.; Coelfen, H.; Xu, A. W.; Dong, W. F. Cryst. Growth Des. 2004, 4, 33. (10) Yu, S. H.; Antonietti, M.; Coelfen, H.; Hartmann, J. Nano Lett. 2003, 3, 379. (11) Wu, X.; Du, J.; Li, H.; Zhang, M.; Xi, B.; Fan, H.; Zhu, Y.; Qian, Y. J. Solid State Chem. 2007, 180, 3288. ¨ ger, N.; Dickerson, M. B.; Ahmad, G.; Cai, Y.; Haluska, M. S.; (12) KrO Sandhage, K. H.; Poulsen, N.; Sheppard, V. C. Angew. Chem., Int. Ed. 2006, 45, 7239. (13) Lee, S.-Y.; Gao, X.; Matsui, H. J. Am. Chem. Soc. 2007, 129, 2954. (14) Banfield, J. F.; Welch, S. A.; Zhang, H.; Ebert, T. T.; Penn, R. L. Science 2000, 289, 751. (15) Tsukazaki, A.; Ohtomo, A.; Onuma, T.; Ohtani, M.; Makino, T.; Sumiya, M.; Ohtani, K.; Chichibu, S. F.; Fuke, S.; Segawa, Y.; Ohno, H.; Koinuma, H.; Kawasaki, M. Nat. Mater. 2005, 4, 42. (16) Lin, H.; Tzeng, S.-J.; Hsiau, P.-J.; Tsai, W.-L. Nanostruct. Mater. 1998, 10, 465. (17) Huang, M. H.; Mao, S.; Feick, H.; Yan, H.; Wu, Y.; Kind, H.; Weber, E.; Russo, R.; Yang, P. Science 2001, 292, 1897. (18) Zu, P.; Tang, Z. K.; Wong, G. K. L.; Kawasaki, M.; Ohtomo, A.; Koinuma, H.; Segawa, Y. Solid State Commun. 1997, 103, 459. (19) Li, Y.; Meng, G. W.; Zhang, L. D.; Phillipp, F. Appl. Phys. Lett. 2000, 76, 2011. (20) Gao, P. X.; Lao, C. S.; Hughes, W. L.; Wang, Z. L. Chem. Phys. Lett. 2005, 408, 174. (21) Gao, T.; Wang, T. H. Appl. Phys. A: Mater. Sci. Process. 2005, 80, 1451. (22) Tian, Z. R.; Voigt, J. A.; Liu, J.; McKenzie, B.; McDermott, M. J. J. Am. Chem. Soc. 2002, 124, 12954. (23) Pan, Z. W.; Dai, Z. R.; Wang, Z. L. Science 2001, 291, 1947. (24) Gao, P. X.; Ding, Y.; Mai, W. J.; Hughes, W. L.; Lao, C. S.; Wang, Z. L. Science 2005, 309, 1700. (25) Liu, B.; Zeng, H. J. Am. Chem. Soc. 2004, 126, 16744.

J. Phys. Chem. B, Vol. 113, No. 17, 2009 6053 (26) Mo, M.; Yu, J. C.; Zhang, L.; Li, S.-K. A. AdV. Mater. 2005, 17, 756. (27) Zhou, J.; Xu, N. S.; Wang, Z. L. AdV. Mater. 2006, 18, 2432. (28) Ito, M. Biomaterials 1991, 12, 41. (29) Orstavik, D.; Hongslo, J. K. Biomaterials 1985, 6, 129. (30) Osamu, Y. Int. J. Inorg. Mater 2001, 3, 643. (31) Stoimenov, P. K.; Klinger, R. L.; Marchin, G. L.; Klabunde, K. J. Langmuir 2002, 18, 6679. (32) Umetsu, M.; Mizuta, M.; Tsumoto, K.; Ohara, S.; Takami, S.; Watanabe, H.; Kumagai, I.; Adschiri, T. AdV. Mater. 2005, 17, 2571. (33) Huang, Z.; Zheng, X.; Yan, D.; Yin, G.; Liao, X.; Kang, Y.; Yao, Y.; Huang, D.; Hao, B. Langmuir 2008, 24, 4140. (34) Oguz, B.; Ozge, M.; Yarkin, O.; Aysegul, B. Eue. J. Pharm. Biopharm. 2005, 60, 373. (35) Panilaitis, B.; Altman, G. H.; Chen, J.; Jin, H. J.; Karageorgiou, V.; Kaplan, D. L. Biomaterials 2003, 24, 3079. (36) Chen, X.; Shao, Z.; Marinkovic, N. S.; Miller, L. M.; Zhou, P.; Chance, M. R. Biophys. Chem. 2001, 89, 25. (37) Gage, L. P.; Manning, R. F. J. Biol. Chem. 1980, 255, 9444. (38) Tanaka, K.; Kajiyama, N.; Ishikura, K.; Waga, S.; Kikuchi, A.; Ohtomo, K.; Takagi, T.; Mizuno, S. Protein Struct. Mol. Enzymol. 1999, 1432, 92. (39) Mita, K.; Ichimura, S.; Zama, M.; James, T. C. J. Mol. Biol. 1988, 203, 917. (40) Bhat, N. V.; Nadiger, G. S. J. Appl. Polym. Sci. 1980, 25, 921. (41) Gerstel, P.; Hoffmann, R. C.; Lipowsky, P.; Jeurgens, L. P. H.; Bill, J.; Aldinger, F. Chem. Mater. 2006, 18, 179. (42) Vanheusden, K.; Warren, W. L.; Seager, C. H.; Tallant, D. R.; Voigt, J. A.; Gnade, B. E. J. Appl. Phys. 1996, 79, 7983. (43) Monticone, S.; Tufeu, R.; Kanaev, A. V. J. Phys. Chem. B 1998, 102, 2854. (44) Brayner, R.; Ferrari-Iliou, R.; Brivois, N.; Djediat, S.; Benedetti, M. F.; Fie´vet, F. Nano Lett. 2006, 6, 866. (45) Chiarini, A.; Petrini, P.; Bozzini, S.; Pra, I. D.; Armato, U. Biomaterials 2003, 24, 789. (46) Minoura, N.; Aiba, S.; Higuchi, M.; Gotoh, Y.; Tsukada, M.; Imai, Y. Biochem. Biophys. Res. Commun. 1995, 208, 511.

JP808805W