CotA laccase immobilized on functionalized magnetic graphene oxide nano-sheets for efficient biocatalysis

In this work, a novel type of functionalized magnetic graphene oxide (MGO) nano-sheets which have the ability to capture His-tagged CotA laccase was synthesized. Nα,Nα-Bis(carboxymethyl)- l -lysine hydrate (NTA-NH 2 ) was attached on MGO then chelated with Ni 2+ and Cu 2+ separately. The Cu 2+ -chelated MGO (MGO-NTA-Cu 2+ ) exhibited the highest adsorption capacity of 177   mg/g-support when compared with both MGO and Ni 2+ -chelated MGO (MGO-NTA-Ni 2+ ) which exhibited an adsorption capacity of 49.9 and 145   mg/g-support, respectively. CotA laccase immobilized on MGO-NTA-Cu 2+ nano-sheets showed the highest activity recovery when compared with that immobilized on MGO-NTA-Ni 2+ nano-sheets. The catalytic properties of MGO-NTA-Cu-CotA laccase were significantly improved in comparison with those of the free laccase. MGO-NTA-Cu-CotA laccase showed efficient decolorization for Congo Red (CR), and the decolorization rate reached 100% after 5   h reaction at 60   °C and pH 8. Furthermore, MGO-NTA-Cu-CotA laccase retained 89.4% of its initial activity after 10 consecutive cycles. Together these results indicated that the Cu 2+ chelated MGO nano-sheets are promising support for efficient CotA laccase immobilization for environmental and industrial applications under high temperature and alkaline condition.