Magnetic Poly(VPA-co-EGDMA)-TiO2 Polymeric Microspheres as Supports for Acetylcholinesterase Immobilization: Kinetic Behavior, Stability, and Reusability

Magnetic poly(vinylphosphonic acid-co-ethylene glycol dimethacrylate)-TiO2 [m-poly(VPA-co-EGDMA)-TiO2] microspheres were synthesized by suspension polymerization and evaluated as supports for direct acetylcholinesterase (AChE) immobilization. The microspheres were characterized by SEM, FT-IR, BET, XRD, XPS, VSM, and zeta potential analyses and exhibited porous morphology, magnetic responsiveness, a specific surface area of 195 m2 g−1, and a swelling ratio of 40.19%. AChE was immobilized mainly through physical adsorption and multipoint non-covalent enzyme–support interactions. The optimum pH was pH 10 for both free and immobilized AChE. Under the tested assay conditions, immobilized AChE showed apparent kinetic parameters of Km = 0.028 mM and Vmax = 0.132 EU.mL−1. Immobilized AChE retained 58.2% of its initial activity after 60 days at 4 °C and 24% after 20 reuse cycles. Overall, the microspheres offer a magnetically recoverable support for AChE immobilization, although further optimization is required to improve kinetic performance and long-term operational stability.