Combination of deep eutectic solvent and organic–inorganic hybrid monomer to prepare monolith for improvement of hydrophilic protein extraction

Two kinds of monomers based on deep eutectic solvents (DESs) and 3-aminopropyl triethoxysilane-methacrylic acid (APTES-MAA) have been synthesized and used to prepare hybrid monoliths for hydrophilic protein extraction. A typical polymerization system consists of APTES-MAA (hybrid monomer), choline chloride/methacrylic acid (MAA) [DES monomer]), and ethylene glycol dimethacrylate (EDMA) in the presence of binary porogens of PEG 20,000 and methanol. The combined effect of the DES monomer and hybrid monomer in the monolithic column material was demonstrated by the recovery of bovine serum albumin (BSA). Compared with the DES/APTES-MAA-free monolith, the poly(APTES-MAA-co-DES-co-EDMA) monolith displayed a higher recovery of 95.5% (relative standard deviation < 5.0%). Monolith-characterization studies including field emission scanning electron microscopy, nitrogen adsorption, and thermal gravimetric analysis showed that the simultaneous use of DES and hybrid monomer to prepare monolith formed a unique structure. The study on the affinity of the monolithic column to protein was carried out by extracting BSA, ovalbumin (OVA), cytochrome c (Cyt c), avidin, and horseradish peroxidase (HRP). Experimental results demonstrated that the proposed poly(APTES-MAA-co-DES-co-EDMA) monolith performed significantly better in the extraction of hydrophilic proteins (BSA, Cyt c, and avidin) than the hydrophobic protein (HRP) and amphiphilic protein (OVA). The separation performance of poly(APTES-MAA-co-DES-co-EDMA) monolith against the hydrophilic acidic protein and basic protein was evaluated using sodium dodecyl sulfate–polyacrylamide gel electrophoresis. The successful extraction of BSA from calf serum was also achieved using the resulting monolith as a solid-phase extraction adsorbent. Thus, poly(APTES-MAA-co-DES-co-EDMA) monolith could be a potential material to extract proteins according to their hydrophilicity/hydrophobicity and for further separation based on their acidity/basicity.