Electrochemical and Solid-State Letters, 10 共1兲 J1-J3 共2007兲
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1099-0062/2006/10共1兲/J1/3/$20.00 © The Electrochemical Society
ZnO-Based Cyclodextrin Sensor Using Immobilized Polydiacetylene Vesicles C. W. Lee,a H. Choi,a M. K. Oh,a D. J. Ahn,a,z J. Kim,a J.-M. Kim,b F. Ren,c,* and S. J. Peartond,* a
Department of Chemical and Biological Engineering, Korea University, Seoul 136-701, South Korea Department of Chemical Engineering, Hanyang University, Seoul 133-791, South Korea Department of Chemical Engineering and dDepartment of Materials Science and Engineering, University of Florida, Gainesville, Florida 32611, USA b c
We report that polydiacetylenes 共PDAs兲 vesicles were successfully immobilized and chemisorbed on single crystal ZnO surfaces. Immobilized PDAs on ZnO were found to be sensitive to temperature and selectively sensitive to ␣- and ␥-cyclodextrins. This approach is attractive for the on-chip integration of various types of sensors, ultraviolet light emitting diodes, and transparent electronics with PDAs. © 2006 The Electrochemical Society. 关DOI: 10.1149/1.2364306兴 All rights reserved. Manuscript submitted June 2, 2006; revised manuscript received June 30, 2006. Available electronically November 1, 2006.
Recently there has been intense interest in the development of ZnO for applications in ultraviolet 共UV兲 light emitters, transparent high power electronics, transparent electrodes in displays, and in photovoltaic devices, piezoelectric transducers, and chemical and gas sensing.1-5 In addition, ZnO is lattice matched to InGaN at an In composition of 22%, allowing for integration of the two materials to provide enhanced functionality.1 An example would be combining visible or UV light-emitting diodes with fluorescent chemical or biological detectors and off-chip wireless communications circuitry. ZnO of reasonable quality can also be deposited at lower growth temperatures than GaN, leading to the possibility of transparent junctions on cheap substrates, such as glass. This may lead to lowcost UV lasers with important applications in high-density data storage systems, solid-state lighting where white light is obtained from phosphors excited by blue or UV light-emitting diodes, secure communications, and biodetection. ZnO is attractive for sensing applications because of its wide bandgap 共3.2 eV兲, the availability of heterostructures, the ease of synthesizing nanostructures and the biosafe characteristics of this material. Recently, the first applications in pH sensor and gas sensor using ZnO were published.4,5 ZnO is a transparent substrate, which makes it easier to monitor the chemistry occurring on the surface from backside using the optical spectroscopy, compared with opaque GaAs and Si substrates. For these reasons, there is significant interest in ZnO-based chemical and biological sensors. After the first report of polydiacetylene 共PDA兲 supramolecules as an influenza virus sensor, the applications of PDAs as chemosensors and biosensors have been a subject of much recent research.6-8 Polydiacetylene has been known for its unique property that “bluephase” polydiacetylene does not fluoresce but its counterpart “redphase” is fluorescent. The phase transition from blue-phase to redphase happens in response to many stimuli from environments such as temperature,7 pH,8 and ligand-receptor interactions.9 We recently reported the unique effects of cyclodextrins on the formation and colormetric transition of polydiacetylene vesicles as well as the new approach for the immobilization of PDA on glass.10-12 Furthermore, the functionalized PDAs can be used as chemosensors to monitor ion, glucose, protein and E. Coli.13 Because the immobilized PDA supramolecule showed better sensitivity against smaller amount of target analytes than PDA solution, it would be advantageous to integrate immobilized PDA in micrometer-size regions with ZnObased devices.
electron concentration of 9 ⫻ 1016 cm−3 and mobility of 200 cm2 /V s. To immobilize PDA on the ZnO surface, the ZnO was first cleaned with acetone and ethanol. Then, the Zn-face surface of ZnO was treated using an ozone plasma for 30 min to remove surface hydrocarbons. After ozone treatment, ZnO was dipped in an amine solution 共3-aminopropyltriethoxysilane:ethanol = 1:10 in volume ratio兲 for 4 h. When the contact angle was measured against pure water 共pH 5.5, room temperature兲 after this process, it was 65.5° 共Fig. 1兲. Then, it was dipped in a solution containing 1 mg N-hydroxysuccinimidobiotin dissolved in 1 mL dimethysulfoxide and 3 mL phosphate buffered saline 共PBS; pH 7.2兲. for 2 h and avidin for another 2 h. At this point, the surface of ZnO was ready for the immobilization of supramolecules 共here, vesicles兲 after the treatments of biotin and avidin 共Fig. 2a兲. To make selfassembled surface patterns of the vesicles, PCDA-ABA 共10,12-pentacosadiynoic acid-aminobutyric acid兲:PCDA-biotin共10, 12-pentacosadiynoic acid-2,2⬘-共ethylenedioxy兲-bis-共ethylamide兲biotin兲兲 =9:1 was used to fabricate vesicles through a standard sonication method.14 The size distribution of the vesicles was measured by light scattering to be mono-modal and the average size was ⬃169 nm. A microarrayer 共Nano-plotter from Gesim兲 was employed for patterning to immobilize vesicle on the ZnO surface. After the supramolecule 共self-assembled PCDA-ABA:PCDABiotin兲 was deposited on the ZnO surface, the supramolecule/ZnO hybrid structure was exposed to UV light of 254 nm for polymerization at the intensity of 1 mW/cm2 for 5 min. Finally, the formed PDA supramolecular surface pattern arrays were immobilized and chemisorbed on ZnO surface 共Fig. 2b兲. To confirm the immobiliza-
Experimental The bulk ZnO hexagonal-phase single crystals from Cermet, Inc. were 1 cm2 in dimension and were nominally undoped with 300 K
* Electrochemical Society Fellow. z
E-mail:
[email protected]
Figure 1. 共Color online兲 Contact angle measurement against pure water 共pH 5.5, room temperature兲 after dipping in amine solution for 4 h.
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Electrochemical and Solid-State Letters, 10 共1兲 J1-J3 共2007兲
Figure 2. 共Color online兲 共a兲 Schematic procedure of surface treatment with biotin and avidin and 共b兲 immobilization of PDA vesicles on ZnO.
tion, ZnO was washed with deionized water and heated to 110°C to stimulate PDA supramolecules, which are responsive to a threshold temperature.
biotin兲兴 is only sensitive to ␣-CD,10 two pieces of functionalized ZnO were dipped in each ␣- and ␥-CD solutions for 30 min. Figure 5 shows that our immobilized PDA is only sensitive to ␣-CD, which is confirmed from red fluorescence measurements by a fluorescence
Results and Discussion Figure 3 shows that no fluorescence image was detectable before heating, but there was a well-defined fluorescence image after thermal treatment, which confirmed two things, namely, that PDAs pattern arrays 共spot size = 250 m兲 were successfully immobilized on the ZnO surface and second, that they were responsive to temperature. Because we know that the polymerized vesicles were immobilized on the ZnO surface, we tried to use it for cyclodextrin 共CD兲 sensing because these CDs have different binding specificities against ␣- and ␥-CDs, which make it valuable to study the ligandreceptor interactions. These were then tested for selectivity. Figure 4 shows the structures of each CD. Because PCDA-ABA 关one of components of supramolecule 共self-assembled PCDA-ABA:PCDA-
Figure 3. 共Color online兲 Fluorescence image after thermal treatment to confirm the immobilization of PDA vesicles on ZnO.
Electrochemical and Solid-State Letters, 10 共1兲 J1-J3 共2007兲
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Figure 4. Structures of ␣- and ␥-CDs.
microscope 共Olympus BX51; excitation at 480–550 nm and emission at 580 nm兲 共Fig. 5, left兲. By sharp contrast, there was no fluorescence from PDA-immobilized ZnO after dipped in ␥-CD solution 共Fig. 5, right兲. Conclusions PDA vesicle was successfully immobilized on the surface of ZnO single-crystal substrates. The regions on which the PDA was immobilized were as small as 250 m and were achieved by chemisorption. PDA pattern arrays on ZnO showed the same function as PDA solutions, which is sensitive to a number of environmental parameters. For example, PDA on ZnO was responsive to temperature and selectively sensitive to ␣-CD, but not to ␥-CD. This is an important first step in the application of the PDA vesicle system extended to ZnO-based chemical sensors and to the integration with ZnO-based microelectronics.
Figure 5. 共Color online兲 Fluorescence images showing selective detection of ␣-CD 共left兲 over ␥-CD 共right兲.
Acknowledgments The research at Korea University was supported by Brain Korea 21 program in 2006, a Korea University Grant Fund, KRF, and MOH. The work at Hanyang University was supported by KOSEF 共Basic research Program兲. The work at UF is partially supported by AFOSR, F49620-03-1-0370, by ARO DAAD19-01-1-0603, AFOSR 共F49620-02-1-0366 and F49620-03-1-0370兲, NSF共CTS-0301178, monitored by Dr. M. Burka and Dr. D. Senich兲, 共DMR 0400416, Dr. L. Hess兲 References 1. S. J. Pearton, D. P. Norton, K. Ip, Y. W. Heo, and T. Steiner, J. Vac. Sci. Technol. B, 22, 932 共2004兲. 2. J. E. Nause, III-V’s Review, 12, 28 共1999兲. 3. D. Look, Mater. Sci. Eng., B, 80, 383 共2001兲. 4. L. C. Tien, P. W. Sadik, D. P. Norton, L. F. Voss, S. J. Pearton, H. T. Wang, B. S. Kang, F. Ren, J. Jun, and J. Lin, Appl. Phys. Lett., 87, 222106 共2005兲. 5. B. S. Kang, F. Ren, Y. W. Heo, L. C. Tien, D. P. Norton, and S. J. Pearton, Appl. Phys. Lett., 86, 112105 共2005兲. 6. D. H. Charych, J. O. Nagy, W. Spevak, and M. D. Bednarski, Science, 261, 585 共1993兲 7. D. J. Ahn, E.-H. Chae, G. S. Lee, H.-Y. Shim, T.-E. Chang, K.-D. Ahn, and J. M. Kim, J. Am. Chem. Soc., 125, 8976 共2003兲. 8. Q. Cheng and R. C. Stevens, Langmuir, 14, 1974 共1998兲. 9. S. K. Hobbs and G. Shi, M. D. Bednarski, Bioconjugate Chem., 14, 526 共2003兲. 10. J.-M. Kim, J.-S. Lee, J.-S. Lee, S.-Y. Woo, and D. J. Ahn, Macromol. Chem. Phys., 206, 2299 共2005兲. 11. J.-M. Kim, Y. B. Lee, D. H. Yang, J.-S. Lee, G. S. Lee, and D. J. Ahn, J. Am. Chem. Soc., 127, 17580 共2005兲. 12. J.-M. Kim, E.-K. Ji, S.-M. Woo, H. Lee, and D. J. Ahn, Adv. Mater. (Weinheim, Ger.), 15, 1118 共2003兲 13. Z. Ma, J. Li, M. Liu, J. Cao, Z. Zou, J. Tu, and L. Jiang, J. Am. Chem. Soc., 120, 12678 共1998兲. 14. J.-M. Kim, J.-S. Lee, H. Choi, D. Sohn, and D. J. Ahn, Macromolecules, 38, 9366 共2005兲.
