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Langmuir 2007, 23, 4728-4731
Recyclable Hydrophilic-Hydrophobic Micropatterns on Glass for Microarray Applications Hua Zhang, Yong Yeow Lee, Kwong Joo Leck, Namyong Y. Kim,* and Jackie Y. Ying* Institute of Bioengineering and Nanotechnology, 31 Biopolis Way, The Nanos, Singapore 138669 ReceiVed December 29, 2006. In Final Form: March 4, 2007 A novel method for fabricating recyclable hydrophilic-hydrophobic micropatterns on glass chips is presented. TiOx patterns (100-2000 µm) were sputtered on glass chips via a through-hole mask. The patterned chips were then vapor-coated with fluoroalkylsilane, for example, (heptadecafluoro-1,1,2,2-tetrahydrodecyl)triethoxysilane (FTES) to form a hydrophobic coating layer. The fluoroalkyl chain of FTES film on TiOx patterns was photocleaved under UV irradiation, exposing the fresh hydrophilic TiOx patterns. The resulting chip could be used multiple times by repeating the coating and photocleaving processes with negligible deterioration of the hydrophobic FTES film coated on glass. If desired, bare glass patterns could also be generated by removing the TiOx patterns with KOH. The patterned glass chips have been successfully used for microarray fabrication.
Microarrays of biomaterials consisting of either DNA, proteins, or cells have found widespread applications in disease diagnosis,1,2 pathogen detection,3,4 biomarker discovery,5,6 and biomolecular interaction analysis.7 Often the scope and performance of biomicroarrays are determined by the quality of coatings employed for surface patterning. Patterned surfaces have been fabricated by many methods including microcontact printing (µCP),8-13 microfluidic lithography (µFL),8,9,14-19 and conventional photolithography.9,10,20 However, they have limited practical applications due to several disadvantages. For example, µCP and µFL lack reliability and consistency, particularly in industrial scale-up. Furthermore, these methods are often incompatible with popular coating conditions as they involve long exposure to organic solvents or high-temperature vapor-phase deposition. Conventional photolithographic methods for surface patterning limit the range of coating reagents and methods available due to the presence of photoresist films. In addition, the photoresist * Corresponding authors. E-mail:
[email protected] (J.Y.Y.);
[email protected] (N.Y.K.). Phone: (+65) 6824-7000. Fax: (+65) 6478-9080. (1) MacGregor, P. F. Expert ReV. Mol. Diagn. 2003, 3, 185. (2) Lorenzi, C.; Tubazio, V.; Serretti, A.; De Ronchi, D. Curr. Genomics 2004, 5, 499. (3) Kostrzynska, M.; Bachand, A. Can. J. Microbiol. 2006, 52, 1. (4) Stoughton, R. B. Annu. ReV. Biochem. 2005, 74, 53. (5) Kingsmore, S. F. Nat. ReV. Drug DiscoVery 2006, 5, 310. (6) Devarajan, P.; Mishra, J.; Supavekin, S.; Patterson, L. T.; Potter, S. S. Mol. Genet. Metab. 2003, 80, 365. (7) Satoh, J.; Nanri, Y.; Yamamura, T. J. Neurosci. Methods 2006, 152, 278. (8) Kane, R. S.; Takayama, S.; Ostuni, E.; Ingber, D. E.; Whitesides, G. M. Biomaterials 1999, 20, 2363. (9) Falconneta, D.; Csucsb, G.; Grandina, H. M.; Textor, M. Biomaterials 2006, 27, 3044. (10) Gaspar, S.; Schuhmann, W.; Laurell, T.; Csoregi, E. ReV. Anal. Chem. 2002, 21, 245. (11) Stevens, M. M.; Mayer, M.; Anderson, D. G.; Weibel, D. B.; Whitesides, G. M.; Langer, R. Biomaterials 2005, 26, 7636. (12) Foley, J.; Schmid, H.; Stutz, R.; Delamarche, E. Langmuir 2005, 21, 11296. (13) Xia, Y.; Whitesides, G. M. Angew. Chem., Int. Ed. 1998, 37, 550. (14) Andersson, H.; van den Berg, A. Sens. Actuators B 2003, 92, 315. (15) Hung, P. J.; Lee, P. J.; Sabounchi, P.; Aghdam, N.; Lin, R.; Lee, L. P. Lab Chip 2005, 5, 44. (16) Rhee, S. W.; Taylor, A. M.; Tu, C. H.; Cribbs, D. H.; Cotmanb, C. W.; Jeon, N. L. Lab Chip 2005, 5, 102. (17) Murthy, S. K.; Sin, A.; Tompkins, R. G.; Toner, M. Langmuir 2004, 20, 11649. (18) Ohashi, R.; Otero, J. M.; Chwistek, A.; Hamel, J. F. P. Electrophoresis 2002, 23, 3623. (19) Tourovskaia, A.; Figueroa-Masot, X.; Folch, A. Lab Chip 2005, 5, 14. (20) Falconnet, D.; Koenig, A.; Assi, F.; Textor, M. AdV. Funct. Mater. 2004, 14, 749.
films may leave residual materials on the surface, which can either interfere with or complicate subsequent surface coating. Most importantly, these patterned surfaces can be used only once despite the significant fabrication cost and time involved. Herein we report a convenient, recyclable, and reliable method for fabricating hydrophilic-hydrophobic micropatterns on glass chips. Our method takes advantage of the photocatalytic activity of TiOx21-25 in generating and recycling surface patterns. Recently, Tadanaga et al. reported superhydrophilic-superhydrophobic micropatterns on a TiOx surface using the sol-gel method.26 Although it is attractive, this approach presents a few challenges when applied to bio-microarrays.27 First, the hydrophobic coating on TiOx tends to deteriorate under ambient atmosphere due to the photocatalytic activity of TiOx. Second, precise alignment is required for the recycling of hydrophilically patterned areas. Third, it is difficult to generate a naked glass surface for the immobilization of biomolecules where desired. Last, the surface has not been demonstrated for use with biological applications. In this paper, we propose a flexible and convenient method for generating hydrophilic-hydrophobic micropatterns on glass chips. In addition, we show that the chip can be used for biological applications, such as cell attachment and growth. Scheme 1 shows the method we have developed to generate hydrophilic-hydrophobic micropatterns on glass chips. In a typical experiment, a 4 in. Pyrex 7740 glass wafer was diced to rectangular chips with dimensions of 38 mm × 18 mm. After cleaning with piranha solution (H2SO4/H2O2 volume ratio ) 7:3) at 110 °C for 0.5 h, the chip was rinsed with Milli-Q H2O and dried with N2. Next, the cleaned glass chips were coated with TiOx at room temperature or at 500 °C using a homemade sputter via a mask with through-holes of 100-2000 µm diameter (step A in Scheme 1). This step produced patterned coatings of amorphous TiOx or a mixture of anatase-amorphous TiOx on the glass surface.28,29 The power of the Ti source was 200 W. The Ar and O2 gas flow rates were 25.2 and 10.8 standard cm3, (21) Wang, H.; Wu, Y.; Xu, B. Q. Appl. Catal. B 2005, 59, 139. (22) Gu, Z. Z.; Fujishima, A.; Sato, O. Angew. Chem., Int. Ed. 2002, 41, 2067. (23) Carp, O.; Huisman, C. L.; Reller, A. Prog. Solid State Chem. 2004, 32, 33. (24) Masuda, Y.; Sugiyama, T.; Koumoto, K. J. Mater. Chem. 2002, 12, 2643. (25) Masuda, Y.; Ieda, S.; Koumoto, K. Langmuir 2003, 19, 4415. (26) Tadanaga, K.; Morinaga, J.; Matsuda, A.; Minami, T. Chem. Mater. 2000, 12, 590. (27) See Supporting Information for details on generating chemical patterns on TiOx.
10.1021/la063759i CCC: $37.00 © 2007 American Chemical Society Published on Web 03/30/2007
Letters
Langmuir, Vol. 23, No. 9, 2007 4729 Scheme 1. Schematic of Surface Patterning
respectively. The chamber pressure for sputtering was 2 mTorr. Upon sputtering for 1-5 min, a pattern of 5-20 nm thick TiOx film was formed on the glass chip.30 Next, the TiOx-patterned glass chips were vapor-coated with (heptadecafluoro-1,1,2,2tetrahydrodecyl)triethoxysilane (FTES) (Gelest, Inc., Morrisville, PA) at 115 °C for 2 h under 1 mTorr of pressure to form a hydrophobic coating (step B in Scheme 1).31 The thickness of the FTES film was 1-2 nm as determined by ellipsometry. Functioning as a photocatalyst,21-23 TiOx can oxidize organic adsorbates under UV irradiation. The photocleaving of the FTES film on the TiOx would change the surface property from hydrophobic to hydrophilic.26 Figure 1 shows the change in the contact angle of water on bulk FTES-coated, amorphous TiOxcoated, or mixed TiOx-coated glass surfaces with increasing UV irradiation time (wavelength ) 254 nm, 120 mJ/cm2, XL-1500 UV Crosslinker with six 15-watt UV-C tubes, Krackeler Scientific, Inc., Albany, NY). The FTES film on both amorphous and mixed TiOx films demonstrates similar profiles of degradation. After 2 h of UV irradiation, the advancing angle changed from 119 ( 2° to 0°, suggesting the complete removal of the hydrophobic FTES film from the surface. During UV irradiation, the difference between advancing and receding angles increased dramatically before both angles approached 0°. This result was expected as the chemical non-uniformity of a surface would be
Figure 1. Advancing and receding contact angle (CA) of water on mixed anatase-amorphous TiOx surface and amorphous TiOx surface subjected to different UV irradiation periods. The uncertainty in CA measurements is (2°. Small contact angles of
