Reactive monolayers for surface gradients and biomolecular patterned interfaces

Self-assembled monolayers (SAMs) are an excellent platform to implement and develop interfacial reactions for the preparation of versatile materials of pivotal importance for the fabrication of, among others, biochips, sensors, catalysts, smart surfaces and electronic devices. The development of methods for selective, efficient, simple and rapid surface transformations with control over the surface composition is still a fundamental challenge in surface science. The research described in this thesis is aimed at the fabrication and investigation of functional and reactive SAM-based platforms for the development of bioactive monolayers and surface chemical gradients. In the first part (Chapters 3-4), a thiol-reactive fluorogenic platform has been employed for the simultaneous immobilization and detection of bioactive ligands and proteins. In particular, this system allowed the selective and sensitive signaled immobilization of active peptides for cell adhesion and cell differentiation studies. Moreover, this method has been used to fabricate patterned protein arrays with control over the protein orientation via covalent and non-covalent immobilization strategies. In the second part (Chapters 5-8), electrochemically derived concentration gradients of a catalyst (Cu(I)) in solution have been employed to make micron-scale surface gradients by means of the surface-confined copper(I)-catalyzed azide-alkyne 1,3-dipolar cycloaddition. The system allowed mapping of the reaction kinetics in space and direct visualization of the reaction order. Additionally, the shape of the surface chemical gradients was tuned by the reaction conditions. The fabrication of a pH-sensitive platform allowed the in-situ visualization and quantification of micron-scale pH gradients induced by the electrolysis of water. Combination of the thiol-reactive fluorogenic platform and the micron-scale surface gradient fabrication method provided a supramolecular platform that allowed the first experimental evidence of superselectivity in a multivalent host-guest system. In summary, the results described in this thesis demonstrate the power of reactive monolayers to provide valuable tools for biological applications and to control the local surface composition by the fabrication of surface gradients. In both cases, the reactive SAMs allow the systematic investigation of micron-scale physicochemical phenomena at interfaces. Reactive monolayers thus constitute a valuable tool for the modification of surfaces leading to new functionalities and novel materials. We expect that future developments will show new functionalization schemes in particular by the integration of dynamic systems in the fabrication processes, thus providing spatiotemporal control over the surface composition and properties and allowing to tackle unique challenges in surface science and biology.