Impact of functionalization linker chemistry on cellulase immobilization: a comparative study of TEOS, APTS, and MPTS functionalized magnetic nanoparticles

Magnetic nanobiocatalysts based on Fe₃O₄ nanoparticles coated with tetraethyl orthosilicate (TEOS) and functionalised with (3-aminopropyl)triethoxysilane (APTS) or (3-mercaptopropyl)trimethoxysilane (MPTS) were developed for cellulase immobilisation and systematically evaluated. Physicochemical characterisation confirmed successful surface modification, while adsorption studies showed that MNPs@TEOS-MPTS achieved the highest immobilisation capacity (q_e = 1.06 mg mg⁻¹) with fast kinetics following a pseudo-second-order model, whereas MNPs@TEOS-APTS displayed lower loading (q_e = 0.94 mg mg⁻¹) and diffusion-limited behaviour. Enzymatic assays revealed that MNPs@TEOS-APTS exhibited the highest catalytic activity (1.92 U g⁻¹) under optimal conditions (pH 5, 50 °C), but with reduced tolerance to alkaline pH, while MNPs@TEOS-MPTS showed slightly lower initial activity (1.61 U g⁻¹) combined with enhanced thermal resistance and operational stability. Reusability tests highlighted MNPs@TEOS–MPTS as the most robust system, retaining 62% of its initial activity after six cycles, compared to 33% for MNPs@TEOS–APTS and 52% for MNPs@TEOS. Molecular docking analysis supported these findings, indicating higher binding affinity for APTS associated with favourable catalytic orientation, whereas MPTS promoted multiple stabilising interactions that increased conformational rigidity. Overall, the results demonstrate that ligand chemistry critically governs the balance between catalytic efficiency and long-term stability, providing rational guidelines for the design of magnetic nanobiocatalysts tailored to industrial applications.