Polymeric Nanogels for Selenite Delivery and Release in Foliar Biofortification: Experimental and Theoretical Insights into Polymer–Ion Interactions

Abstract This work reports an integrated experimental and theoretical study of polymeric nanogels as tunable colloidal platforms for selenite binding and controlled ion delivery. Three formulations (N600, N3000, and Nmix) form stable colloidal dispersions (120–260 nm) with structure and interfacial properties governed by polymer architecture and network composition. Performance is evaluated under foliar application in Eruca sativa as a proof-of-concept system, showing enhanced selenium uptake and reduced phytotoxicity compared to free selenite. N600 exhibits the most balanced behavior, combining moderate binding strength, efficient ion release, and high compatibility. Multitechnique characterization and density functional theory (DFT) calculations reveal that selenite interaction with the polymer network is governed by coupled polymer–ion interactions, proton-transfer equilibria, and solvation effects. At pH 5.5, where HSeO3– predominates, binding is dynamic and reversible, enabling polymer-mediated selenium delivery. N3000 and Nmix show stronger stabilization via proton-transfer-assisted interactions, whereas N600 is dominated by weaker electrostatic association, consistent with polymer protonation state and pKa-dependent behavior. The results demonstrate that the balance between ion stabilization and mobility governs binding and release behavior. This study provides molecular-level insight into polymer–ion systems and establishes design principles for tunable colloidal platforms for controlled ion delivery.