A dual-responsive silica-based molecularly imprinted polymer for sustainable and specific adsorption of γ-aminobutyric acid from Moringa oleifera seeds.

A thermos/pH-responsive molecularly imprinted polymer based on polydopamine-modified ethylenediamine-N-propyl-bonded silica gel (PDA@EDAS-MIP) was developed as a solid-phase extraction (SPE) adsorbent for the selective separation of γ-aminobutyric acid (GABA) from Moringa oleifera seeds. In the design of PDA@EDAS-MIP, a PDA layer formed via self-polymerization on the EDAS surface created a dense waterproof barrier that protected the silica-based matrix against water-induced corrosion and significantly reduces silicon leaching. Additionally, this PDA layer serves as a secondary reaction platform for the covalent grafting of MIP. Subsequently, N-isopropylacrylamide (NIPAM) and acrylic acid (AAc) were employed as the thermo-responsive and pH-responsive functional monomers, respectively. Above the lower critical solution temperature (LCST, 45 °C), NIPAM chains shrink to restore the complete imprinted cavities while below the LCST (25 °C), NIPAM chains swell to destroy the imprinted cavities. Electrostatic attraction exists between GABA and AAc at pH 6, whereas electrostatic repulsion occurs at pH 8. AAc also interacts with GABA through hydrogen bonding and van der Waals forces. The dual-responsive characteristics endow PDA@EDAS-MIP with excellent adsorption capacity of 28.74 mg/g and desorption efficiency of 97.8%. The novel SPE column filled with PDA@EDAS-MIP successfully enriched GABA from Moringa oleifera seed with a recovery ratio of 94.1%. In addition, the PDA@EDAS-MIP SPE column exhibits good recyclability and the relative adsorption ratio remained above 80% after 10 repeated uses. This study provides an effective strategy for silica-based MIP to achieve a specific recognition and efficient adsorption-desorption capability in aqueous environments.