Bienzyme Magnetic Nanobiocatalyst with Fe³⁺-Tannic Acid Film for One-Pot Starch Hydrolysis

In this study, a novel co-immobilization biocatalyst for one-pot starch hydrolysis was prepared through shielding enzymes on the Fe₃O₄/SiO₂ core-shell nanospheres by a Fe³⁺-tannic acid (TA) film. In brief, α-amylase and glucoamylase were covalently immobilized on amino-modified Fe₃O₄/SiO₂ core-shell nanospheres using glutarldehyde as a linker. Then, a Fe³⁺-TA protective film was formed through the self-assembly of the Fe³⁺ and TA coordination complex (Fe³⁺-TA@Fe₃O₄/SiO₂-enzymes). The film acts a "coating" to prevent the enzyme from denaturation and detachment, thus significantly improving its structural and operational stability. Furthermore, the immobilization efficiency reached 90%, and the maximum activity recovery of α-amylase and glucoamylase was 87 and 85%, respectively. More importantly, the bienzyme magnetic nanobiocatalyst with Fe³⁺-TA film could be simply recovered by a magnet. The Fe³⁺-TA@Fe₃O₄/SiO₂-enzymes kept 55% of the original activity after reuse for 9 cycles, indicating outstanding reusability. However, the bienzyme magnetic nanobiocatalyst without Fe³⁺-TA film maintained 28% of the initial activity.