Biocatalytic Performance of pH‐Sensitive Magnetic Nanoparticles Derived from Layer‐by‐Layer Ionic Self‐Assembly of Chitosan with Glucoamylase

Based on the characteristics of polycations of chitosan and glucoamylase, which are oppositely charged, they were successfully alternatingly deposited onto the surface of aldehyde‐modified Fe₃O₄ nanoparticles by using a layer‐by‐layer ion exchange method to form magnetic carriers to construct multilayer films (designated as Fe₃O₄@(CS/GA)_n). The (CS/GA)_n film systems were endowed with the pH‐dependent properties of chitosan as well as the catalytic activity of glucoamylase. The changes in weight loss and surface chemistry, morphology, and magnetic sensitivity were monitored and verified by UV/Vis spectroscopy, zeta potential, TEM, and a vibrating sample magnetometer. Subsequently, the influence of the number of bilayers, storage stability, pH, temperature, and reusability of Fe₃O₄@(CS/GA)₅ biocatalysts on catalytic activity were investigated. The results from characterization and determination remarkably indicate that Fe₃O₄@(CS/GA)₅ presents excellent catalytic activity, storage stability, pH stability, and reusability in comparison with free enzyme. Fe₃O₄@(CS/GA)₅ retained >60 % of its initial activity at 65 °C over 6 h; the optimum temperature and pH also increased to the ranges of 45–65 °C and 2.5–3.5, respectively, and only 27 % activity was lost after 10 cycles. This new strategy simplifies the reaction protocol and improves encapsulation efficiency and catalytic activity for new potential applications in biotechnology.