Langmuir 2006, 22, 11275-11278
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3D-Ordered Macroporous Materials Comprising DNA Linglu Yang, Juan Kang, Yuan Guan, Fang Wei, Shuo Bai, Maofeng Zhang, Zhifeng Zhang, and Weixiao Cao* The Key Laboratory of Polymer Chemistry and Physics of Ministry of Education, College of Chemistry and Molecular Engineering, Peking UniVersity, Beijing 100871, China ReceiVed May 31, 2006. In Final Form: August 9, 2006 Macroporous materials comprising DNA were fabricated with the colloidal crystal template. First, DNA and diazoresin (DR) molecules are fully filled into the voids of a colloidal crystal template. After thermal treatment and removal of the colloids, DNA porous materials with highly ordered structure were obtained. In the process of thermal treatment the cross-linking reaction takes place between DR and DNA, which plays an important role for sustaining the porous framework. The DNA porous materials will turn into a fluorescent DNA/dye composite after staining with Hoechst 33258 (Hoe), a characteristic fluorescent dye for DNA. This kind of composite DNA porous material may have potential applications in optical devices.
Introduction Three-dimensional (3D)-ordered macroporous materials have attracted increasing attention due to their unique properties and diverse potential applications, ranging from photonic crystals to advanced adsorbents, catalysts, and bioassays.1-5 A strategy to create macroporous materials is based on the replication of the colloidal crystal template with ∼26% voids in volume.6-8 Through filling the voids with other materials and then removing the colloids, a variety of porous materials with precisely controlled pore size and highly ordered 3D structure, such as metals,1 metallic oxides,2 inorganic semiconductors,3 ceramics,4 and polymers,5 have been prepared. However, deoxyribonucleic acids (DNA) and proteins are scarcely selected to fabricate 3D-ordered macroporous materials due to their worse crystallization or weak interaction between the molecules. Once the colloids are removed, the porous structures will collapse completely. DNA is a well-known biopolymer with a special double helix structure. It not only can serve as a carrier of genetic information in all living organisms but also has important and unique applications in material fields. For example, it is an anionic polyelectrolyte with phosphate in its backbone and can deposit easily with cationic polyelectrolytes to form self-assembly films. DNA-based films may be important in separation, ion transportation, and biosensors.9-13 Moreover, owning to having plenty of bonding sites (base pairs and phosphate groups), DNA has been successfully employed for the fabrication of metallic or semiconducting nanowires14-17 which may be interesting as a (1) Velev, O. D.; Tessier, P. M.; Lobo, R. F.; Lenhoff, A. M.; Kaler, E. W. Nature 1999, 401, 548. (2) (a) Velev, O. D.; Jede, T. A.; Lobo, R. F.; Lenhoff, A. M. Nature 1997, 389, 447. (b) Holland, B. T.; Blanford, C. F.; Stein, A. Science 1998, 281, 538. (3) (a) Braun, P. V.; Wiltzius, P. Nature 1999, 402, 603. (b) Vlasov, Y. A.; Bo, X.; Sturm, J. C.; Norris, D. J. Nature 2001, 414, 289. (4) Zakhidov, A. A.; Baughman, R. H.; Iqbal, Z.; Cui, C.; Khayrullin, I.; Dantas, S. O.; Marti, J.; Ralchenko, V. G. Science 1998, 282, 897. (5) (a) Johnson, S. A.; Ollivier, P. J.; Mallouk, T. E. Science 1999, 283, 963. (b) Wang, D.; Caruso, F. AdV. Mater. 2001, 13, 350. (6) Liang, Z.; Susha, A. S.; Caruso, F. AdV. Mater. 2002, 14, 1160. (7) Cardoso, A. H.; Leite, C. A. P.; Zaniquelli, M. E. D.; Galembeck, F. Colloids Surf. A 1998, 144, 207. (8) Bardosova, M.; Tredgold, R. H. J. Mater. Chem. 2002, 12, 2835. (9) Nishimura, N.; Ohno, H. J. Mater. Chem. 2002, 12, 2299. (10) Yamada, M.; Kato, K.; Nomizu, M.; Sakairi, N.; Ohkawa, K.; Ya-mamoto, H.; Nishi, N. Chem. Eur. J. 2002, 8, 1407. (11) Ohno, H.; Nishimura, N.; J. Electrochem. Soc. 2001, 148, E168. (12) Lvov, Y.; Decher, G.; Sukhorukov, G. Macromolecules 1993, 26, 5396. (13) Wang, L.; Yoshida, J.; Ogata, N. Chem. Mater. 2001, 13, 1273. (14) Braun, E.; Eichen, Y.; Sivan U.; Ben-Yoseph, G. Nature 1998, 391, 775.
miniature circuit component. Woolley et al. fabricated discrete three-branched metal nanostructures as precursors for threeterminal nanoelectronic devices using DNA as a template.17 Furthermore DNA is also valuable for photonic applications. Grote et al. found that various optical dyes can be inserted into the double helix of DNA to form waveguide materials with excellent nonlinear optical properties.18 Therefore, DNA macroporous material, as a new type of DNA material, is expected to be important for fundamental investigation and technology application. However, to our best knowledge there is no successful example of preparing DNA porous material from the colloidal crystal template. In this article, we provide an effective and easy method to build up DNA porous material. First the DNA and DR were filled into the voids of opal to form a composite colloidal crystal via a vertical deposition method. For enhancing the strength of the DNA framework, a thermotreatment process was employed to form cross-linked structure between DR (a thermal-sensitive polyelectrolyte)19 and DNA. After removal of the colloids by solvents, the 3D-ordered macroporous DNA/DR material was obtained. The main preparation processes are illustrated schematically in Scheme 1. On the basis of this porous DNA/DR material, we prepared the fluorescent DNA/dye composite material by staining with Hoe. This kind of fluorescent porous material may have practical applications in optical devices. Experimental Section Materials. Double-stranded DNA (herring sperm, Sigma.) and Hoechst 33258 (Hoe) are commercial available and were used as received. DR and monodisperse polymer colloids were synthesized according to our previous reports described elsewhere.19,20 Preparation of DNA/DR Porous Material. The colloidal crystal template on Si substrate was prepared using polymer beads of (pstyrene-methyl methacrylate-3-sulfopropyl methacrylate, potassium salt) as a building block according to literature.21 The template should (15) Monson C. F.; Woolley A. T. Nano Lett. 2003, 3, 359. (16) Nyamjav, D.; Ivanisevic, A. Biomaterials 2005, 26, 2749. (17) Becerril, H. A.; Stoltenberg, R. M.; Wheeler, D. R.; Davis, R. C.; Harb, J. N.; Woolley, A. T. J. Am. Chem. Soc. 2005, 127, 2828. (18) Grote, J. G.; Diggs, D. E.; Nelson, R. L.; Zetts J. S.; Hopkins, F. K.; Ogata, N.; Hagen, J. A.; Heckman, E.; Yaney, P. P.; Stone, M. O.; Dalton, L. R. Mol. Crystals Liquid Crystals 2005, 426, 3. (19) Cao, S. G.; Zhao, Ch.; Cao,W. X. Polym. Int. 1998, 44, 142. (20) Yang, L. L.; Cong, H. L.; Cao, W. X. Acta Polymeric Sinica 2005, 2, 223.
10.1021/la0615645 CCC: $33.50 © 2006 American Chemical Society Published on Web 11/04/2006
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Scheme 1. Schematic Representation of the Main Processes to Prepare Macroporous DNA/DR Material
Scheme 2. Schematic Representation of the Cross-Linking Reaction between DNA and DR in Thermal Treatment
be heated at 80 °C for 30 min to form the connection among spheres and enhance its stability. Then it was inserted vertically into an aqueous solution composed of 3.5 mL DNA (1 mg/mL, pH 4.6) and 15 µL DR aqueous solution (2 mg/mL) in a 10 mL vessel. The composite colloidal crystal filled with DNA and DR was achieved after water evaporated thoroughly at ∼25 °C. Then it was heated at 70 °C for 24 h to make DNA and DR cross-link. Finally, the colloids were removed with tetrahydrofuran (THF) to obtain the 3D-ordered porous DNA/DR material. Preparation of Fluorescent DNA/Dye Porous Material. The obtained porous DNA/DR material was immersed in Hoe aqueous solution (0.1 mg/mL) for 15 min in dark at room temperature, rinsed with deionized water thoroughly, and air-dried. In this case, Hoe molecules were inserted into the double helix of DNA to form fluorescent DNA/dye porous material. Characterization. Scanning electron microscopy (SEM) images were taken on a field-emission environmental scanning electron microscope (FEI, Quanta 200) at 15 kV. Normalized UV-vis reflectance spectra were recorded on a Shimadzu-1800 spectrometer with reflectance spectroscopy accessory. Fluorescence images and spectra were collected on an Olympus BX-60M fluorescence microscope. The color images of the porous material were obtained with a CCD microscope system (Sony XC-999P, Japan) under perpendicular irradiation of white light.
porous DNA/DR material was obtained (Figure 1c). We can clearly observe the perfect pore framework. A triangular pattern below every hole can be visualized because each hole just locates above three holes of the nether layer. If we remove the colloids without thermal treatment, we can only obtain a planar DNA film (Figure 1d) resulting from the collapsed pores. Therefore, the thermal treatment (at 70 °C for 24 h) is necessary for obtaining a robust porous material. In this process the columbic interaction between DNA and DR will convert to the covalent bond22 to form a covalently cross-linked structure. The cross-linking reaction is illustrated schematically in Scheme 2.
Results and Discussion Figure 1a shows the colloidal crystal with FCC (face center cubic) packing used as a template in this article, composed of the polymer beads (∼280 nm in diameter) and the voids (darker regions of Figure 1a). Figure 1b shows the composite colloidal crystal in which the voids have been filled completely with DNA and DR molecules. After treatment of the composite colloidal crystal at 70 °C and removal of the colloids, the 3D-ordered (21) Cong, H. L.; Cao W. X. Langumir 2003, 19, 8177.
Figure 1. SEM images of (a) colloidal crystal template; (b) composite colloidal crystal; (c) porous DNA/DR material prepared from b after thermal treatment; (d) planar DNA film resulted from b without thermal treatment.
3D-Ordered Macroporous Materials Comprising DNA
Figure 2. (a) normalized reflectance spectra of composite colloidal crystal (curve 1) and DNA/DR porous material (curve 2); (b) the CCD image of the ordered porous DNA/DR material.
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Figure 3. FL image (a) and spectrum (b) of porous DNA/dye material.
The normalized reflectance spectra of the composite colloidal crystal and porous material are shown in Figure 2a. The main photon band gaps (PBG) of them locate at 688 nm (curve 1) and 542 nm (curve 2), respectively. The appearance of PBG indicates that they both have long-length ordered structure in large areas. The CCD image of DNA/DR porous material is shown in Figure 2b. The brilliant green color originating from Bragg diffraction of the ordered structure is consistent with the wavelength of its PBG (542 nm). It was found that various optical dyes inserted into the double helix of DNA molecules rendered waveguide materials with excellent nonlinear optical properties.18 In addition, 3D-ordered porous structure also can modulate the optical emission in some unique way.23-27 Therefore, DNA/dye 3D-ordered porous materials are very attractive in view of their applications in optical devices. Hoe, a characteristic fluorescent dye of DNA, can bind with DNA through groove-binding interaction.28 By means of immersing DNA porous material in Hoe solution, we obtained a fluorescent DNA/Hoe porous material. The FL image (a) and spectrum (b) of them are shown in Figure 3. The bright green areas (Figure 3a) show that DNA has been stained with Hoe (22) Li, Q.; OuYang, J. H.; Chen, J. Y.; Zhao, X. Sh.; Cao, W. X. J. Polym. Sci. A: Polym. Chem. 2002, 40, 222. (23) Blanco, A.; Lopez, C.; Mayoral, R.; My´guez, H.; Meseguer, F.; Mifsud, A.; Herrero, J. Appl. Phys. Lett. 1998, 73, 28. (24) Lodahl, P.; Van Driel, A. F.; Nikolaev, I. S.; Irman, A.; Overgaag, K.; Vanmaekelbergh, D.; Vos, W. L. Nature 2004, 430, 654. (25) Vlasov, Y. A.; Luterova, K.; Pelant, I.; Honerlage, B.; Astratov, V. N. Appl. Phys. Lett. 1997, 71, 1616. (26) Solovyev, V. G.; Romanov, S. G.; Sotomayor Torres, C. M.; MXller, M.; Zentel, R.; Gaponik, N.; EychmXller, A.; Rogach, A. L. J. Appl. Phys. 2003, 94, 1205. (27) Gaponik, N.; Eychmuller, A.; Rogach, A. L.; Solovyev, V. G.; Sotomayor Torres, C. M.; Romanov, S. G. J. Appl. Phys. 2004, 95, 1029. (28) Zhou, Y. L.; Li, Y. Z. Langmuir 2004, 20, 7208.
Figure 4. SEM images of the DNA/DR porous material after immersing in water for 24 h, (a) without further treatment with DR solution; (b) further treatment with DR solution.
successfully. The black irregular stripes are the crevices originating from the colloidal crystal template. The λmaxF of the porous material sits at 492 nm (Figure 3b) and shifts ∼20 nm to the shorter wavelength as compared with that of Hoe in aqueous solution (512 nm). The DNA/DR porous material has good stability in N,Ndimethylformide (DMF) but will be partly destroyed (Figure 4a)
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after immersion in water for a long time (24 h). It was considered that the porous DNA material cross-linked with small amount of DR (see Experimental Section) is difficult to withstand the etching from water for a long time. To further enhance the waterresistance of DNA porous material, it was treated once again with DR solution (100 mg/mL). In this process more DR molecules can infiltrate into the porous framework. After treating it at 70 °C for 24 h, the porous material becomes very robust and can maintain its framework completely after immersing in water for 24 h (Figure 4b).
crystal and then removing the colloids with THF after thermal treatment. The covalently cross-linking structure is a critical factor to maintain the 3D porous framework. The UV-reflection spectra and CCD images show that the porous material has longlength ordered structure in large areas. DNA porous material can become a fluorescent composite material after staining with Hoechst 33258, which may have important applications in optical devices. The stability of DNA porous materials against water can be improved greatly with the further treatment of DR solution.
Conclusions
Acknowledgment. The authors are grateful to the NSFC for financial support of this work (Grant No: 90406018).
The 3D-ordered macroporous DNA/DR material was prepared through infiltrating DNA and DR into the voids of the colloidal
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