Characteristics of glucose oxidase immobilized on carbon-encapsulated iron nanoparticles decorated with polyethyleneimine

This study aimed to conjugate glucose oxidase (GOX) with carbon-encapsulated iron nanoparticles (Fe@C) which were functionalized with carboxylic groups and decorated with branched polyethyleneimine (PEI), in order to yield Fe@C-NH-PEI-GOX and Fe@C-(CH2)2-CONH-PEI-GOX derivatives. The process of electrostatic attachment of the GOX enzyme on the Fe@C-NH-PEI and Fe@C-(CH2)2CONH-PEI constructs was optimized, and the amount of enzyme attached on the constructs was also estimated. The steady-state kinetics of β-D-glucose oxidation by molecular oxygen, a reaction catalyzed by GOX, were compared using a native GOX enzyme obtained from Aspergillus niger and nanoparticles-conjugated GOX. The Fe@C-NH-PEI-GOX and Fe@C-(CH2)2-CONH-PEI-GOX constructs were formed by electrostatic interaction between positively charged Fe@C-NH-PEI and Fe@C-(CH2)2-CONH-PEI and negatively charged GOX in water media at pH 6. The activity of the immobilized enzyme on Fe@C-NH-PEI-GOX and Fe@C-(CH2)2-CONH-PEI-GOX derivatives was preserved, with Km values of 3271 and 1605 µM, respectively. However, the catalytic activity of Fe@C-NH-PEI-GOX and Fe@C-(CH2)2-CONH-PEI-GOX was reduced up to 20- and tenfold in comparison to that of the free GOX enzyme. The results of the study suggest that PEI is a promising cationic polymer with a high loading capacity and that the use of a simple adsorption process for preparing Fe@C-NH-PEI-GOX and Fe@C-(CH2)2-CONH-PEI-GOX conjugates is a highly efficient approach for stable immobilization of GOX enzyme on carbon-encapsulated iron nanoparticles.