In
this study, a facile, yet effective surface-engineering method
was reported to confer graphene oxide (GO) nanosheets with amphiphilic
feature and numerous binding sites toward enzymes for biphasic reactions
in Pickering emulsions. Briefly, the surface of GO nanosheet is first
modified and simultaneously reduced by polydopamine to endow with
catechol groups. A portion of catechol groups is utilized to anchor
zeolitic imidazolate framework 8 (ZIF-8) nanoparticles onto the polydopamine-modified
graphene oxide (P-rGO) nanosheets through Zn2+–catechol
coordination. The remaining uncoordinated catechol groups in P-rGO
nanosheets are utilized to immobilize lipase onto the P-rGO nanosheets
through chemical conjugation. The resulting two-dimensional P-rGO/ZIF-8/Lipase
nanobiocatalysts with an enzyme loading percent values of 34.05–48.75%
could be spontaneously assembled at the oil/water interface, which
were then utilized to catalyze the hydrolysis of water-insoluble p-nitrophenyl palmitate (p-NPP) into water-soluble p-nitrophenol (p-NP). The Pickering emulsions,
which were robustly stabilized by P-rGO/ZIF-8/Lipase, facilitated
the diffusion of p-NP from the oil/water interface
to aqueous phase, acquiring an enzymatic activity recovery of ∼60%.
Moreover, P-rGO/ZIF-8/Lipase exhibited remarkably enhanced stabilities
against multiple reuses and various harsh conditions compared with
free lipase, GO/Lipase, and P-rGO/Lipase, showing great potential
in practical applications.