Solvent-driven sod-ZIF-8 ↔ ZIF-C phase transformation preserves nucleic acid functionality for gene delivery

Abstract

Metal–organic frameworks (MOFs) built from zinc ions and 2-methylimidazole (HmIM) are widely explored carriers for gene delivery. Although preliminary reports show phase-dependent properties, often studies label distinct crystalline phases as “ZIF-8” and overlook how routine washing steps influence the property-to-function relationship. Here, we examine in depth how solvent history tunes the crystal phase and biological performance in plasmid DNA (pDNA) encapsulated in Zn–mIM carriers. An aqueous biomimetic mineralization at 25 °C (HmIM : Zn²⁺ = 4 : 1) yields defect-rich sodalite (sod) ZIF-8 with an ∼80% encapsulation efficiency of the input plasmid and four times the loading obtained from an identical ethanolic synthesis. Post-synthetic solvent washes or aging govern phase transformations: media containing ≥70% water trigger a solution-mediated transformation into a carbonate–imidazolate framework (ZIF-C), whereas absolute ethanol stabilizes sod ZIF-8 topology. Despite the extensive recrystallization processes into chemically distinct solids, pDNA loss remains ≤12% for sod → ZIF-C and ≤20% for ZIF-C → sod transformation. The green fluorescent protein (GFP) assays confirm that the recovered pDNA retains full transcriptional activity. Comparative cytotoxicity tests on PC-3 cells show that water-aged ZIF-C sustains ≥85% viability and superior colloidal stability, while ethanol-stabilized sod-ZIF-8 possesses a higher pDNA loading and an on-demand burst release upon first contact with water. By examining how post-processing with ethanol/water yields pure sod, mixed sod/ZIF-C, and pure ZIF-C carriers, this work provides the first solvent-phase guide for MOF gene carriers and establishes simple washing protocols as tools to tune release kinetics, stability, and biocompatibility without altering the ZIF precursors or the reaction temperature. By enabling phase-engineered DNA@ZIF carriers with predictable gene-delivery performance, this study advances MOF-mediated nucleic acid therapies toward reproducible biomedical applications.