Chemically Robust, Primary Amine Rich Mussel-Inspired Nanoscale Coatings via a Cation-π Interaction Independent Pathway

Polydopamine (PDA) coatings have emerged as a versatile surface modification strategy owing to their substrate-independent coating capability and aqueous processability. However, the stability of conventional PDA coatings is primarily determined by weak cation-π interactions, which render them inherently unstable under strongly basic conditions or in highly polar aprotic solvents. This interaction-dominated nature fundamentally limits their chemical robustness and practical applicability. Here, we report a cation-π interaction-independent route for catechol-based coating strategy that replaces weak noncovalent interactions with chemically fixed covalent networks. By coupling catechol with diamine building blocks at pH 11, a cation-free condition, via a Michael addition reaction, we construct oligo(catechol)-diamine coatings in which C-N covalent linkages serve as the dominant structural backbone and driving force for coating formation. This reaction-driven, fast-coating strategy yields smooth, conformal ultrathin films that remain stable in strong bases (pH > 10), polar aprotic solvents, and nonpolar organic media. Importantly, the resulting coatings retain accessible primary amine groups at the surface, enabling postfunctionalization, while also significantly suppressing fluorescence quenching by tuning the diamine length. This fully aqueous, scalable approach provides a chemically robust and economically viable alternative to conventional PDA and silane-based coatings, offering a new framework for designing stable functional materials.