A sustainable platform of polydopamine-functionalization of alkali-activated halloysite nanotubes for efficient β-glucosidase immobilization

Halloysite nanotubes (HNTs), naturally abundant clay minerals with unique tubular structures and biocompatibility, offer significant potential as an enzyme immobilization matrix. Conventional functionalization methods often involve energy-intensive processes or compromise enzyme activity, however. The study offers an approach to functionalizing HNTs via alkali activation and polydopamine (PDA) coating for efficient immobilization of β-glucosidase (BG). Alkali treatment enhanced surface hydroxyl density and defect sites, while PDA deposition through mild oxidative polymerization provided a reactive interface for covalent enzyme conjugation mediated by N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride (EDC) crosslinking. Structural characterization (XRD, FTIR, SEM-EDS) confirmed successful PDA coating and enzyme binding while preserving the crystalline integrity of HNTs. At an optimal loading of 167 mg g –1 support , the immobilization efficiency was 83% with retained activity. The immobilized BG not only exhibited optimal catalytic performance at pH 6.0 and 60°C but also enhanced stability against pH/temperature fluctuations through immobilization. Kinetic analysis revealed a 39% increase in V max (4.73 vs 3.40 mM L –1 min –1 ) and sustained substrate affinity (K m =10.4 mM L –1 ). The biocatalyst retained ≥84% activity after 30 days of storage at 4°C and 53% activity over six re-use cycles, attributed to the rigid enzyme conformation stabilized by covalent PDA coupling and HNTs confinement. The research results presented are expected to broaden the application scope of halloysite in the field of enzyme catalysis and provide a feasible solution for improving the catalytic stability of β-glucosidase.