Facile co-immobilization of laccase and mediator by polyethyleneimine-induced biomimetic mineralization for dye removal

Laccase, a green biocatalyst, has been widely used in the field of biodegradation with the assistance of electron mediators. Herein, a novel strategy, polyethyleneimine (PEI)-induced biomimetic mineralization, was explored and applied to co-immobilize laccase and 2,2′-azino bis (3-ethylbenzothiazoline)-6-sulfonic acid (ABTS). With the PEI doping, calcium phosphate (CaP) could facilely mineralize within 20 min to form PEI@CaP; ABTS could be co-mineralized with PEI to form (PEI + ABTS)@CaP. Laccase, a negatively charged protein, was then immobilized via electrostatic adsorption onto the embedded PEI in the carriers. Both of the immobilized laccase preparations, denoted as Lac-PEI@CaP and Lac-(PEI + ABTS)@CaP, showed high activity recoveries (96.4 % and 88.0 %, respectively), and increased pH tolerance and storage stability as compared to free laccase. ABTS and laccase loading densities of Lac-(PEI + ABTS)@CaP reached 0.83 mmol g−1 and 100 mg g−1, respectively. Lac-(PEI + ABTS)@CaP presented higher malachite green (MG) degradation capability than free laccase and Lac-PEI@CaP with free ABTS, possibly due to the proximity effect of the co-immobilized laccase and ABTS. Moreover, Lac-(PEI + ABTS)@CaP exhibited reusability and kept 83.2 % of MG degradation activity after three recycles and 37.9 % in the sixth. This work provided a new strategy for the co-immobilization of laccase and electron mediator, and demonstrated the potential of the biocatalyst for organic pollutant removal.