Chemically-Gated and Sustained Molecular Transport through Nanoporous Gold Thin Films in Biofouling Conditions.

Sustained release and replenishment of the drug depot are essential for the long-term functionality of implantable drug-delivery devices. This study demonstrates the use nanoporous gold (np-Au) thin films for in-plane transport of fluorescein (a small-molecule drug surrogate) over large (mm-scale) distances from a distal reservoir to the site of delivery, thereby establishing a constant flux of molecular release. In the absence of halides, the fluorescein transport is negligible due to a strong non-specific interaction of fluorescein with the pore walls. However, in the presence of physiologically relevant concentration of ions, halides preferentially adsorb onto the gold surface, minimizing the fluorescein-gold interactions and thus enabling in-plane fluorescein transport. In addition, the nanoporous film serves as an intrinsic size-exclusion matrix and allows for sustained release in biofouling conditions (dilute serum). The molecular release is reproducibly controlled by gating it in response to the presence of halides at the reservoir (source) and the release site (sink) without external triggers (e.g., electrical and mechanical).