Hierarchical functional gradients of pH-responsive self-assembled monolayers using dynamic covalent chemistry on surfaces.

Surface chemistry is an important field of research, especially for the study and design of (bio)nanostructures in which nearly every atom lies at an interface. Here we show that dynamic covalent chemistry is an efficient tool for functionalizing surfaces in such a way that their interfacial properties can be varied controllably in space and time. Modulation of pH is used to tune the fast, selective and reversible attachment of functional amines (with different pK(a) values) to an aldehyde-coated surface. To illustrate the potential of this technique, we developed dynamic self-assembled monolayers ('DynaSAMs'), which enable the hierarchical construction of mixed gradients comprising either small functional molecules or proteins. Control of the (bio)chemical composition at any point on the surface potentially provides a simple bottom-up method to access numerous surface patterns with a broad range of functionalities.