Characterization of biofunctional thin films deposited by activated vapor silanization
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osé Pérez-Rigueiro Department of Materials Science, Escuela Te´cnica Superior de Ingenieros (ETSI) Caminos, Canales y Puertos, Universidad Politécnica de Madrid, 28040 Madrid, Spain
Ana Conde Department of Corrosion and Protection, Centro Nacional de Investigaciones Metalúrgicas (CENIM-CSIC), 28040 Madrid, Spain
Aurelio Climent and Raul Gago Centro de Micro-Análisis de Materiales, Universidad Autónoma de Madrid, 28049 Madrid, Spain
Miguel Manso and José M. Martínez-Duart Faculty of Sciences, Department of Applied Physics C-12, Universidad Autónoma de Madrid, 28049 Cantoblanco, Madrid, Spain (Received 28 November 2007; accepted 31 March 2008)
A novel technique based in the combination of vapor silanization and chemical vapor deposition, hereafter referred to as activated vapor silanization (AVS), is shown to be an effective biofunctionalization technique. The AVS process results in thin organic films with a high surface amine concentration when deposited on substrates with different chemical characteristics, such as silicon, porous silicon, or gold. Chemical characterization shows that the films are composed of carbon (hydrocarbon, C–Si, C–C), silicon (different oxidation states), nitrogen (primary and secondary amines), oxygen, and hydrogen. Relevantly, the amines are also distributed along the film thickness, ensuring functionality even after some degradation of the films. AVS films behave practically as monocrystalline silicon substrates under loading–unloading tests. In addition, the AVS films behave as permeable membranes for molecules smaller than 5 Å, and the amine surface concentration is estimated to be 8 NH2/nm2 for molecules of about 12 Å, which is three times higher than that obtained with standard silanization procedures. I. INTRODUCTION
Biomedical applications of materials require development of stable interfaces between their surfaces and the biological systems. Such hybrid interfaces are commonly created by surface modification of the materials through deposition of functional groups, i.e., thiols (–SH), carboxyls (–COOH), or amines (–NH2). Surface modification of materials for the subsequent interaction with biological systems is known as biofunctionalization. Some of the most popular biofunctionalization techniques are self-assembled monolayers (SAMs),1,2 hydrosilylation,3–5 and silanization.6–8 All of these techniques require tight compatibility between the nature of the substrates and the biofunctionalization precursor molecules, so that their application is restricted to a reduced number a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2008.0241 J. Mater. Res., Vol. 23, No. 7, Jul 2008
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of linked materials and molecules. Thus, SAMs are used mainly in the immobilization of thiolated molecules on gold, hydrosilylation employs alkenes or alkynes as precursors to functionalize H-rich substrates, and silanization requires silane-coupling agents to functionalize OHrich surfaces. Among these techni
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