CO₂ and Magnetic Dual-Responsive Microspheres That Reversibly and Selectively Capture Target Proteins under Mild Conditions

CO 2 -responsive polymers transform from hydrophobic to hydrophilic under a gas stimulus, which can be used to capture proteins under mild conditions; however, the selectivity is not high enough. In this work, Fe 3 O 4 enveloped with silicon dioxide (SiO 2 ) was prepared and grafted on poly(2-(diethylamino)ethyl methacrylate) (PDEA) through the atom transfer radical polymerization (ATRP) technique, yielding a CO 2 -responsive magnetic microsphere. The molecularly imprinted surface was then fabricated using poly(dopamine) (PDA) with bovine serum albumin (BSA) as a template, producing gas and magnetic dual-responsive microspheres with good selectivity, denoted as Fe 3 O 4 /SiO 2 /PDEA-MIP. Their chemical structure and CO 2 responsiveness were confirmed. Their adsorption capacity for BSA was 55 mg g –1 under the concentration of 0.8 mg mL –1 with good reversibility. The imprinting factor (IF) reached as high as 5.73 under optimized adsorption conditions, which further makes it specifically capture the target protein from a mixture and separate the protein under gas or magnetic control. The interaction between BSA with unprotonated and protonated PDEA was theoretically studied by quantum mechanics calculations, which prove its reversibility under the CO 2 stimulus. Furthermore, the circular dichroism (CD) spectra approved that the conformation of proteins remained unchanged under the CO 2 stimulus, indicating that it is a moderate separation technique for proteins. This work supplied a strategy to develop highly selective and switchable materials to realize protein recognition and separation under mild conditions.