Conformal vacuum-deposited polymer coatings on nanoporous gold for tunable pH-Dependent release

Official URL: https://dx.doi.org/10.1016/j.vacuum.2026.115615

Engineered nanoporous gold (NPG) surfaces have shown promise for controlled molecular release, however, achieving reproducible surface modification while preserving pore accessibility and scalability remains a key challenge. In this study, NPG, obtained by an atomic gold self-arrangement process, was functionalized with a pH-responsive poly(4-vinylpyridine-co-ethylene glycol dimethacrylate) coating using initiated chemical vapor deposition (iCVD) to enable triggered release of a small-molecule drug surrogate, rose bengal (RB), under varying pH conditions. The polymerization kinetics in vacuum were primarily governed by the surface monomer concentration, and the deposition process preserved the NPG pore morphology while introducing pH-responsive functionality to the surface. Release studies performed at different pH values showed that pristine NPG displayed pH-independent release (∼14% of the total load), whereas c-NPG exhibited pH-triggered burst release of RB with values up to 50% of the total load. Weibull-based kinetic model showed that coating induces changes in release arising from a shift in the balance between the initial burst phase and the later diffusion-controlled regime. This behavior is consistent with a mechanism that involves pH-dependent changes in RB-polymer interactions and swelling-mediated transport hindrance within the responsive coating, demonstrating that vacuum-based pore functionalization can convert a passive porous substrate into a chemically responsive release platform.