DNA-directed enzyme immobilization on Fe3O4 modified with nitrogen-doped graphene quantum dots as a highly efficient and stable multi-catalyst system

The exploration of new tactics for manufacturing artificial immobilized multi-enzyme systems based on enzyme cascades has recently attracted considerable interest because of the urgent need for multi-enzyme catalysts and the high cost of free enzymes. Because of the inevitable limitations of native enzymes such as instability and storage issues, the development of nanozyme–enzyme cascades is needed. A versatile strategy was developed for fabricating an efficient multi-catalyst system by immobilizing glucose oxidase (GO x ) on ferriferous oxide nanocomposites functionalized with nitrogen-doped graphene quantum dots (Fe 3 O 4 @N-GQDs) through DNA-directed immobilization. The Fe 3 O 4 @N-GQDs acted as a carrier for the natural enzyme and showed high peroxidase activity which enabled an enzyme cascade that included GO x to be set up. This multi-catalyst system showed great catalytic activity, reversibility and operational stability. The surfaces of GO x -targeted magnetic nanoparticles were regenerated by mild dehybridization of DNA. The Michaelis constant ( K m ) and maximum initial velocity ( V max ) of the multi-catalyst system were 1.069 mM and 11.2 × 10 −8  M s −1 , respectively, which are considerably better than the corresponding values for adsorbed and free bienzyme combinations. The increased bioactivity of the multi-catalyst system is ascribed to the satisfactory peroxidase-like activity of Fe 3 O 4 @N-GQDs, the enzyme–promoting effect of the QDs and enhancement by DNA-directed immobilization. Because of the diverse range of possible nanozyme–enzyme combinations and high efficiency of this approach, this work provides a novel pathway for the manufacturing of synthetic enzyme catalyst systems, which have great potential in the field of biotechnology.