Lipase immobilization on facile synthesized polyaniline-coated silver-functionalized graphene oxide nanocomposites as novel biocatalysts: stability and activity insights

Abstract

Enzymes perform an essential role in catalysing extensive reactions. Yet, their instability upon repetitive use, as well as their activity inhibition by different solvent remains a cumbersome task. We present here a simple method to immobilize Aspergillus niger lipase (ANL) onto polyaniline–silver functionalized graphene oxide nanocomposites (PANI/Ag/GO), involving the facile synthesis of PANI/Ag/GO and the preparation of ANL@PANI/Ag/GO nanocomposites. Covalent bonding was achieved via glutaraldehyde as a cross linking agent onto these nanocomposites. The resulting ANL@PANI/Ag/GO with a nanoscale dimension has a remarkably high enzymatic activity recovery yield of 88.5% and immobilization yield upto 94%. The apparent optimum temperature and pH for ANL@PANI/Ag/GO were higher than those of free ANL. ANL@PANI/Ag/GO exhibited comparatively higher catalytic efficiency and enzyme–substrate affinity. The binding of ANL on PANI/Ag/GO-NCs was confirmed by Fourier transform infrared spectroscopy, transmission electron microscopy, scanning electron microscopy, dynamic light scattering and atomic force microscopy. The metal content was examined by energy-dispersive X-ray spectroscopy. ANL@PANI/Ag/GO biocatalyst retained over 86% of its initial enzyme activity after 11 repeated uses. ANL@PANI/Ag/GO displayed significantly enhanced solvent tolerance and high thermal stability compared to the free enzyme, it might be due to the increase in enzyme structure rigidity. This remarkable stability and nanobiocatalytic performance in conditions concerning temperature and solvents, will have a deep impact on the industrial scale up of biocatalytic systems.