Amination of surfaces via self-assembly of dopamine.

Catechols can strongly bind to a variety of substrates so as to functionalize the target surfaces by forming self-assembled monolayer. However, catecholic amine might self-oxidize and polymerize at high pH since the amine is susceptible to nucleophilic addition reaction that results in polymerized oligomers on surfaces. Therefore, the availability of amines for further derivation reaction would be restricted to a large extent. Herein, by controlling pH values to avoid self-oxidative polymerization, dopamine (DA) forms thin and surface-adherent monolayers onto a wide range of inorganic and organic materials, including mica, silica, and Au surface, allowing amination of the surfaces that resemble commercially used aminosilanization. The self-assembly process was traced by surface topography and elemental composition analysis using atomic force microscope (AFM), X-ray photoelectron spectroscopy (XPS), and electrochemical characterization (electrochemical impedance spectroscopy and cyclic voltammetry measurements). Then, the aminated surfaces were used for secondary derivation reactions to create a variety of ad-layers, including patterned streptavidin through specific binding interaction with biotin and ferrocene surface via amidation reaction. The surface and interface properties of the obtained surfaces were tested by electrochemical measurements.