Covalent Immobilization of Aspergillus niger Lipase on Epoxy-Activated Silver Oxide Nanoparticles-Impregnated Chitosan Surfaces: Characterization, Stability & Kinetic Studies

The immobilization of Aspergillus niger Lipase (E.C.3.1.1.3) via covalent binding on epoxy-activated chitosan-coated silver oxide nanoparticles (Ag 2 O/Chitosan) under optimized conditions was studied. Ultraviolet–visible spectroscopy, Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction spectral analysis (XRD), Transmission electron microscopy (TEM), Field-emission scanning electron microscopy (FE-SEM), and energy-dispersive X-Ray Microanalysis (EDAX) were employed to characterize the size, structural composition, crystallinity, surface morphologies, & percentage elemental composition of prepared Ag 2 O NPs & Ag 2 O/Chitosan nanocomposites. Optimal immobilization conditions (coupling time (16 h), pH (7.8), activating agent concentration (4% v/v), enzyme concentration (0.6 mg/ml)) were evaluated to acquire maximum expressed activity of bound lipases. The optimum catalytic activity of immobilized & solubilized lipases was exhibited at pH 8.5, 60 °C, and pH 7.0, 45 °C respectively. Thermal stability of immobilized lipases (Ag 2 O/Chitosan-EPI@Lip) preserved 76.47% of catalytic activity at 60 °C after 2 h of incubation while solubilized lipases retained only 40.51% of catalytic activity under similar conditions. Kinetic parameters (K m , V max ) of immobilized (39.69 µM, 21.32 µM/min) & native lipase (34.12 µM, 21.83 µM/min) were determined, demonstrating the enhanced efficacy of lipase after immobilization. Moreover, bound lipases exhibited remarkable reusability and storage stability. Thus, the present methodology suggests that (Ag 2 O/Chitosan-EPI@Lip) bioconjugate would be a potential biocatalyst for promoting sustainable productions & advanced technologies. Graphical Abstract