Biomolecule and Nanoparticle Transfer on Patterned and Heterogeneously Wetted Superhydrophobic Silicon Nanowire Surfaces Gae ¨lle Piret, ² Yannick Coffinier, ² Cle ´ment Roux, ‡ Oleg Melnyk, ‡ and Rabah Boukherroub* ,² Institut de Recherche Interdisciplinaire (IRI, CNRS-USR 3078) and Institut d’Electronique, de Microe ´ lectronique et de Nanotechnologie (IEMN, CNRS-UMR 8520), Cite ´ Scientifique, AVenue Poincare ´ - B.P. 60069, 59652 VilleneuVe d’Ascq, France, and Institut de Biologie de Lille (IBL, CNRS-UMR 8525), 1 rue du Pr. Calmette, 59021 Lille, France ReceiVed December 21, 2007. In Final Form: January 21, 2008 We report on the use of patterned superhydrophobic silicon nanowire surfaces for the efficient, selective transfer of biological molecules and nanoparticles. Superhydrophilic patterns are prepared on superhydrophobic silicon nanowire surfaces using standard optical lithography. The resulting water-repellent surface allows material transfer and physisorption to the superhydrophilic islands upon exposure to an aqueous solution containing peptides, proteins, or nanoparticles. The study of wetting properties on superhydrophobic surfaces is crucial for potential applications including hydrophobic interactions, microfluidic devices, and self-cleaning surfaces. 1-3 Superhydrophobic surfaces display a water advancing contact angle higher than 150° with low hysteresis. A microdroplet deposited on a superhydrophobic surface attains a quasi-spherical shape and accordingly reduces the contact area between the droplet and the solid substrate. The reduced contact area between a superhydrophobic surface and water will have a significant impact on the interfacial chemical and biochemical reactions. We have recently shown that reversible electrowetting can be achieved on superhydrophobic silicon nanowires. 4 The result opens new opportunities for potential applications in the field of lab-on- chip and particularly in the preparation of highly functional microfluidic devices. 5 Patterned surfaces with different wetting properties are useful for the study and manipulation of biomolecules 6 and in the fabrication of microfluidic channels. 7 Surface patterning has been achieved using several means: microcontact printing, photoli- thography, and scanning probes. 8 The difference in the contact angle between the patterns is, however, smaller than 90°, which may limit practical applications of the hydrophilic-hydrophobic patterns. To date, there have been only a few reports on patterned superhydrophobic-superhydrophilic surfaces. 9-13 The contrast in the wetting properties has previously been used to direct polymers selectively to hydrophilic regions of patterned super- hydrophobic surfaces. 13 In this letter, we show that superhydrophilic regions obtained through the photolithographic patterning of superhydrophobic SiNWs allow easy, fast, and selective transfer of peptides, proteins, and gold nanoparticles. The silicon nanowires (SiNWs) investigated in this study were prepared by the chemical etching 14,15 of crystalline silicon in AgNO 3 /HF aqueous solution or using the vapor-liquid-solid (VLS) 4,16,17 growth mechanism, according to previously published work. Figure 1A displays a top-view scanning electron microscopy (SEM) image of the nanowires synthesized by silicon dissolution in AgNO 3 /HF solution. 14,15 The nanowire diameter is in the range of 20-80 nm, as evidenced by the cross-sectional SEM view (Figure 1B). The as-prepared SiNWs, after exposure to the atmosphere, are covered with a thin silicon oxide layer that confers superhydrophilic character to the surface. A water contact angle of <5° was measured for such a surface. Chemical modification of the surface with octadecyltrichlorosilane (OTS) led to the formation of a superhydrophobic surface with a contact angle of 160° with low hysteresis (0-2°) (inset in Figure 1B). 18,19 The surface roughness combined with the low surface energy induced by the surface modification ensured air trapping between the substrate and the liquid droplets, which is necessary to achieve superhydrophobicity. 3-5,18 The contrast between superhydro- philicity and superhydrophibicity is evident in the optical photographs displayed in Figure 2. The as-prepared SiNW * To whom correspondence should be addressed. E-mail: rabah.boukherroub@iemn.univ-lille1.fr. Tel: +33 3 20 19 79 87. Fax: +33 3 20 19 78 84. ² Institut de Recherche Interdisciplinaire (IRI, CNRS-USR 3078) and Institut d’Electronique, de Microe ´lectronique et de Nanotechnologie (IEMN, UMR 8520). ‡ Institut de Biologie de Lille (IBL, CNRS-UMR 8525). (1) Nakajima, A.; Hashimoto, K.; Watanabe, T. Monatsh. Chem. 2001, 132, 31-41. (2) Sun, T.; Feng, L.; Gao, X.; Jiang, L. Acc. Chem. Res. 2005, 38, 644-652. (3) Zhang, X.; Shi, F.; Niu, J.; Jiang, Y.; Wang, Z. J. Mater. Chem., in press. (4) Verplanck, N.; Galopin, E.; Camart, J.-C.; Thomy, V.; Coffinier, Y.; Boukherroub, R. Nano Lett. 2007, 7, 813-817. (5) Verplanck, N.; Coffinier, Y.; Thomy, V.; Boukherroub, R. Nanoscale Res. Lett. 2007, 2, 577-596. (6) Hook, A. L.; Thissen, H.; Voelcker, N. H. Trends Biotechnol. 2006, 24, 417-477. (7) Seeman, R.; Brinkmann, M.; Kramer, E. J.; Lange, F. F.; Lipowsky, R. Proc. Natl. Acad. Sci. U.S.A. 2005, 102, 1848-1852. (8) Xia, Y.; Whitesides, G. M. Angew. Chem., Int. Ed. 1998, 37, 550. (9) Tadanaga, K.; Morinaga, J.; Matsuda, A.; Minami, T. Chem. Mater. 2000, 12, 590-592. (10) Tadanaga, K.; Morinaga, J.; Minami, T. J. Sol-Gel Sci. Technol. 2000, 19, 211-214. (11) Notsu, H.; Kubo, W.; Tatsuma, T. J. Mater. Chem. 2005, 15, 1523-1527. (12) Martines, E.; Seunarine, K.; Morgan, H.; Gadegaard, N.; Wilkinson, C. D. W.; Riehle, M. O. Nano Lett. 2005, 5, 2097-2103. (13) Zhai, L.; Berg, M. C.; Cebeci, F. C.; Kim, Y.; Milwid, J. M.; Rubner, M. F.; Cohen, R. E. Nano Lett. 2006, 6, 1213-1217. (14) Peng, K.; Wu, Y.; Fang, H.; Zhong, X.; Xu, Y.; Zhu, J. Angew. Chem., Int. Ed. 2005, 44, 2737-2742. (15) Peng, K.; Fang, H.; Hu, J.; Wu, Y.; Zhu, J.; Yan, Y.; Lee, S. T. Chem.s Eur. J. 2006, 12, 7942-7947. (16) Cui, Y.; Duan, X.; Hu, J.; Lieber, C. M. J. Phys. Chem. B 2000, 104, 5213. (17) Salhi, B.; Grandidier, B.; Boukherroub, R. J. Electroceram. 2006, 16, 15-21. (18) Coffinier, Y.; Janel, S.; Addad, A.; Blossey, R.; Gengembre, L.; Payen, E.; Boukherroub, R. Langmuir 2007, 23, 1608-1611. (19) Superhydrophobic silicon nanowire surfaces were obtained by chemical functionalization of the native oxide with a 10 -3 M octadecyltrichlorosilane solution in hexane for 16 h at room temperature in a dry-nitrogen-purged glovebox. The resulting surface was rinsed with CHCl3 and i-PrOH and dried in a gentle stream of nitrogen. 1670 Langmuir 2008, 24, 1670-1672 10.1021/la703985w CCC: $40.75 © 2008 American Chemical Society Published on Web 02/06/2008