Magnetic metal-organic frameworks as scaffolds for spatial co-location and positional assembly of multi-enzyme systems enabling enhanced cascade biocatalysis

Magnetic multi-enzyme nanosystems have been prepared via co-precipitation of enzymes and metal-organic framework HKUST-1 precursors in the presence of magnetic Fe3O4 nanoparticles. The spatial co-localization of two enzymes was achieved using a layer-by-layer positional assembly strategy. Glucose oxidase (GOx) and horseradish peroxidase (HRP) were used as the model enzymes for cascade biocatalysis. By controlling the spatial positions of enzymes, three bienzyme nanosystems GOx@HRP@HKUST-1@Fe3O4, GOx-HRP@HKUST-1@Fe3O4 and HRP@GOx@HKUST-1@Fe3O4 were prepared in which GOx and HRP containing layers were in close proximity, either encapsulated in the HKUST-1 inner layer, or immobilized on the HKUST-1 outer shell, or randomly distributed in the two MOF layers. Their properties were characterized by transmission electron microscopy, energy-dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, thermal gravimetric analysis, and zeta potential measurements. The highest activity was observed at pH = 6 and a temperature of 20 degrees C. Thanks to the favorable positioning of enzymes, the GOx@HRP@HKUST1@Fe3O4 nanosystem revealed superior kinetics with a Michaelis constant K-m = 0.8 mmol L-1 and the maximum reaction rate V-max = 11.3 mu mol L-1 min(-1). The enzyme-HKUST-1 conjugates exhibited remarkably high operational stability compared to the free enzymes. This work provides a facile and versatile approach to spatially organized multienzyme systems with well-defined nanostructures and greatly enhanced the overall biocatalytic efficiency.