Enzyme immobilization in Cage-like 3D-network PVA-H and GO modified PVA-H (GO@PVA-H) with stable conformation and high activity

Abstract In this work, polyvinyl alcohol hydrogel (PVA-H) and graphene oxide doped polyvinyl alcohol hydrogel (GO@PVA-H) with cage-like 3D network structure were synthesized by freeze/thaw recycling method and used for the immobilization of horse radish peroxidase (HRP). The variations of the network structures in PVA-H and GO@PVA-H were investigated under varied conditions. With the increasing PVA content (4–12%) and stirring time, both PVA-H and GO@PVA-H were tended to form more uniform pores and cage-like structure as well as smaller channel size. When GO was introduced, the stirring time was reduced to achieve appropriate mixing during the GO@PVA-H synthesis, compared to PVA-H with the same PVA content. HRP could be caged in PVA-H and GO@PVA-H and remained relatively high enzymatic activity. Experimental results showed that the structure and configuration of PVA-H and GO@PVA-H had significant effects on the enzyme accessibility and the conformational transformation of immobilized HRP. The structure analysis showed that the enzymatic conformation of HRP was changed by the immobilization under different conditions. The conformational transformation of immobilized HRP was restrained effectively in GO@PVA-H. After improving the structure of PVA-H and GO@PVA-H, the immobilized HRP acquired high dispersity, good accessibility and stable conformation, showed high-efficient activity similar as free HRP. Compared to PVA-H, not only the immobilization rate of HRP in GO@PVA-H but also the stability and reusability of HRP in the degradation of bisphenol A (BPA) was all improved. Therefore, PVA-H and GO@PVA-H were efficient in terms of storage and recycle of free enzymes in water treatment.