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BACKGROUND Polyethyleneimine (PEI) has attracted wide interest due to not only its good hydrophilicity but also its high density of amino groups across the polymer chain. In order to study in depth the effect of PEI as spacer arm on dye ligand modification and further protein adsorption, poly(methylmethacrylate) (PMMA) magnetic microspheres were fabricated, grafted with PEI, and further modified with an affinity dye‐ligand, Cibacron Blue F3GA (CB). RESULTS CB density of these CB‐PEI‐PMMA microspheres was determined to be 370.7 µmol g‐1 for CB‐PEI 600‐PMMA, 355.2 µmol g‐1 for CB‐PEI 1800‐PMMA, and 317.6 µmol g‐1 for CB‐PEI 70000‐PMMA microspheres, respectively. Moreover, bovine serum albumin (BSA) adsorption capacity of PEI‐PMMA and CB‐PEI‐PMMA microspheres increased greatly compared with PMMA microspheres. The effects of temperature, BSA initial concentration, pH and ionic strength on BSA adsorption were studied. CB‐PEI 70000‐PMMA microspheres exhibited the maximum adsorption of 103.6 mg g‐1. CONCLUSION The results demonstrated the versatility of PEI as spacer arm. The information obtained from the present work could be utilized for rational design of carriers for protein adsorption or enzyme immobilization. © 2017 Society of Chemical Industry

BACKGROUND: To immobilize protein firmly and maintain its native conformation, a 'nano molecular cage' was designed to encapsulate bovine serum albumin (BSA) on the surface of poly(methyl methacrylate) (PMMA) magnetic microspheres by cross-linking poly(ethylene imine) (PEI) chains. RESULTS:The amount of BSA adsorbed on PMMA@PEI microspheres decreased significantly from 70.6 to 7.6 mg g −1 microsphere after desorption under high ionic strength. A similar phenomenon could also be observed for BSA adsorbed on PMMA@PEI-CB (Cibacron Blue F3GA) microspheres. In contrast, the amount of BSA encapsulated in molecular cages only decreased a little after desorption. Furthermore, conformational analysis by Fourier transform infrared spectroscopy (FTIR) showed that the contents of -helices and -sheets decreased slightly by 3.3 and 0.3% respectively on encapsulating BSA in molecular cages. Furthermore, the effects of various factors, including glutaraldehyde amount, cross-linking time and temperature, on BSA encapsulation were investigated. CONCLUSION:The results demonstrated that molecular cages could not only immobilize protein firmly but also maintain its native conformation. Therefore molecular cage encapsulation is suggested to be a potentially valuable protocol in enzyme immobilization. Attachment of CB onto magnetic microspheresCB was attached onto PMMA@PEI magnetic microspheres by nucleophilic reactions between the amino group of PEI and the chloro group of CB. Briefly, 20 mg of PMMA@PEI magnetic microspheres were added into 2 mL of CB solution (3 mg mL −1 ) in a shaker at 160 rpm and 50 ∘ C. To deposit the dye on the microspheres, 140 mg of NaCl was added into the mixture. After 30 min, 100 mg of Na 2 CO 3 was added to speed up the reaction. The reaction was carried out for 4 h. Thereafter, the resulting PMMA@PEI-CB magnetic microspheres were washed with 950 mL L −1 alcohol and distilled water several times until no CB was detected in the supernatant.