One-Step Confined Polymerization of Catecholamine Biopolymers for the Patterned <i>In Situ</i> Growth of Plasmonic Metasurfaces with Single-Particle Resolution

Patterned in situ growth of plasmonic nanostructures is emerging as a rational bottom-up route to fabricating functional plasmonic metamaterials. In this family of approaches, the combination of simple wet-chemistry principles with tailored surface-chemistry modifications unlocks new, scalable, and versatile strategies to produce ordered nanoparticle arrays showing strong electromagnetic responses. Herein, the self-polymerization of catecholamine monomers is exploited to achieve region-specific chemical contrast via a one-step polymer patterning approach that is compatible with different materials and can be completed in a few minutes. To highlight the robustness and versatility of this methodology, the confined polymerization protocol was successfully applied across multiple length scales, from micrometer-sized patterns to nanometric arrays with feature sizes down to a few tens of nanometers, enabling the simultaneous fabrication of multiple patterns on a single substrate within the same preparation. The obtained chemically patterned substrates were exploited to control the gold nanoparticle nucleation point with nanometric precision, leading to the growth of plasmonic arrays. The size of the gold nanoparticles and the number of particles per polymer-patterned feature can be controlled by tuning the growth conditions, underscoring the power of bottom-up wet-chemical in situ approaches for the scalable fabrication of tunable plasmonic architectures showing single-particle resolution (i.e., single nucleation for each active area). The obtained plasmonic metasurfaces exhibit lattice plasmon resonances in the visible and near-infrared spectral regions, reaching quality factors as high as 130. Overall, these results pave the way for advanced sensing, catalytic, and other nanophotonic applications requiring large-area, highly ordered arrays.