Langmuir 2008, 24, 1053-1057
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Functionalized Silicone Nanofilaments: A Novel Material for Selective Protein Enrichment Jan Zimmermann, Michael Rabe, Dorinel Verdes, and Stefan Seeger* Physikalisch-chemisches Institut, UniVersita¨t Zu¨rich Irchel, Winterthurerstrasse 190, CH-8057 Zu¨rich, Switzerland ReceiVed September 26, 2007. In Final Form: October 31, 2007 We present a simple and versatile technique of tailoring functionalized surface structures for protein enrichment and purification applications based on a superhydrophobic silicone nanofilament coating. Using amino and carboxyl group containing silanes, silicone nanofilament templates were chemically modified to mimic anionic and cationic exchange resins. Investigations on the selectivity of the functionalized surfaces toward adsorption of charged model proteins were carried out by means of fluorescence techniques. Due to a high contact area resulting from the nanoroughness of the coating, excellent protein retention characteristics under various conditions were found. The surfaces were shown to be highly stable and reusable over several retention-elution cycles. Especially the full optical transparency and the possibility to use glass substrates as support material open new opportunities for the development of optical biosensors, open geometry microfluidics, or lab-on-a-chip devices.
Introduction Engineering interfaces with unique chemical, physical, and mechanical properties has become a major branch of material science. In this respect the progress in nanotechnology over the past few decades and the ability to manipulate surfaces on the nanometer scale have had a great impact on both science and industry. Currently the development and optimization of new functional materials that facilitate sample preparation and analyte detection in the field of proteomics is an active area of research. 1,2 In these applications a rapid and efficient enrichment of target molecules from complex biological fluids is often the key step to success. As the biochemical interactions of a surface are primarily influenced by its chemical properties, much research has been directed toward selectively modifying the chemistry of solid interfaces. Typical surface functionalities include active groups designed for normal-phase, reversed-phase, ionic exchange, and metal ion affinity chromatography or receptors with specific affinities toward a class of target molecules.3 One example of a versatile technique for tuning the surface chemical properties which has found widespread application is the self-assembled monolayer (SAM) technique.4 With this method, dense layers of functional silanes or thiols can be applied to a variety of surfaces, the most common being oxide surfaces (silica and silicone but also metal oxides) for SAMs of silanes and gold for SAMs of thiols. Apart from its chemical characteristics, the structure and morphology of an interface are crucial parameters determining its overall properties. The wettability of a surface for instance is known to be enhanced by surface roughness.5 Applying a hydrophobic layer to a rough surface can even result in an extremely nonwetting, so-called superhydrophobic surface.6-8 * To whom correspondence should be addressed. Phone: +41 44 6354451. Fax: +41 44 6356813. E-mail:
[email protected]. (1) Xu, Y.; Bruening, M. L.; Watson, J. T. Mass Spectrom. ReV. 2003, 22, 429. (2) Willner, I.; Willner, B.; Katz, E. ReV. Mol. Biotechnol. 2002, 82, 325. (3) Tang, N.; Tornatore, P.; Weinberger, S. R. Mass Spectrom. ReV. 2004, 23, 34. (4) Onclin, S.; Ravoo, B. J.; Reinhoudt, D. N. Angew. Chem., Int. Ed. 2005, 44, 6282. (5) Wenzel, R. N. Ind. Eng. Chem. 1936, 28, 988. (6) Callies, M.; Que´re´, D. Soft Matter 2005, 1, 55. (7) Li, X.-M.; Reinhoudt, D.; Crego-Calama, M. Chem. Soc. ReV., in press.
Furthermore, micro- and nanoscale roughness is known to enhance interfacial phenomena such as cell adhesion or protein adsorption.9,10 Rough surfaces have therefore gained considerable attention as recognition layers in biosensors11-13 and other applications in which the analytical performance is substantially reliant on a large contact area between the analyte solution and functional surface. Tailoring specific nanostructures on solid supports is currently performed to achieve dynamic droplet control,14 to explore the ability of manipulating protein adsorption,15 or to facilitate the immobilization of active biomolecules.12,13,16 As a means to fabricate functionalized high contact area surfaces for applications in proteomics, 1-D nanostructures such as carbon nanotubes and nanofibers are considered to possess great potential.12,13 Whereas carbon nanotubes can only be functionalized at the tip, nanofibers have the additional advantage that their whole surface can be chemically modified.13 A novel class of surface-attached 1-D nanostructures that has only recently been discovered are silicone nanofibers or nanofilaments.17-20 These filaments are essentially highly cross-linked polysiloxane networks and form on surfaces when short-chain trifunctional silanes react in the gas or solvent phase in the presence of water. They distinguish themselves as being simple and inexpensive in (8) Sun, T. L.; Feng, L.; Gao, X. F.; Jiang, L. Acc. Chem. Res. 2005, 38, 644. (9) Kim, P.; Kim, D. H.; Kim, B.; Choi, S. K.; Lee, S. H.; Khademhosseini, A.; Langer, R.; Suh, K. Y. Nanotechnology 2005, 16, 2420. (10) Rechendorff, K.; Hovgaard, M. B.; Foss, M.; Zhdanov, V. P.; Besenbacher, F. Langmuir 2006, 22, 10885. (11) Lion, N.; Rohner, T. C.; Dayon, L.; Arnaud, I. L.; Damoc, E.; Youhnovski, N.; Wu, Z. Y.; Roussel, C.; Josserand, J.; Jensen, H.; Rossier, J. S.; Przybylski, M.; Girault, H. H. Electrophoresis 2003, 24, 3533. (12) Sotiropoulou, S.; Chaniotakis, N. A. Anal. Bioanal. Chem. 2003, 375, 103. (13) Vamvakaki, V.; Tsagaraki, K.; Chaniotakis, N. Anal. Chem. 2006, 78, 5538. (14) Tserepi, A. D.; Vlachopoulou, M. E.; Gogolides, E. Nanotechnology 2006, 17, 3977. (15) Galli, C.; Collaud Coen, M.; Hauert, R.; Katanaev, V. L.; Gro¨ning, P.; Schlapbach, L. Colloids Surf., B 2002, 26, 255. (16) Zhang, J.; Han, Y. Langmuir 2007, 23, 6136. (17) Jung, S.; Artus, G. R. J.; Zimmermann, J.; Seeger, S. Superhydrophobic Coating. WO2004113456, 2004. (18) Artus, G. R. J.; Jung, S.; Zimmermann, J.; Gautschi, H.-P.; Marquardt, K.; Seeger, S. AdV. Mater. 2006, 18, 2758. (19) Gao, L.; McCarthy, T. J. J. Am. Chem. Soc. 2006, 128, 9052. (20) Rollings, D.-a. E.; Tsoi, S.; Sit, J. C.; Veinot, J. G. C. Langmuir 2007, 23, 5275.
10.1021/la702977v CCC: $40.75 © 2008 American Chemical Society Published on Web 12/22/2007
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their fabrication,17-19 can be applied to a large variety of substrate materials,18 and are chemically and environmentally stable.21,22 Research so far has focused mainly on the application of the silicone nanofilaments as superhydrophobic coatings.18,19,21-23 In this work, the potential of the silicone nanofilaments as solid supports for proteomic applications is explored. Glass substrates coated with a dense layer of silicone nanofilaments were functionalized with amino- and carboxysilanes to mimic ionic exchange resins with a high specific surface area. Their performance was evaluated in terms of selectivity, capacity, reproducibility, and chemical stability toward the adsorption of three different model proteins at varying pH values. Experimental Section Materials. Trichloromethylsilane (TCMS), [2-(carbomethoxy)ethyl]trichlorosilane (CETS), and (aminopropyl)triethoxysilane (APTES) were purchased from ABCR and stored and handled in a drybox under a nitrogen athmosphere. Glass slides were purchased from Menzel Gla¨ser and cleaned with detergent solution (Deconex, Borer Chemie) prior to use. Anhydrous toluene (water content
