Nafion membranes as reusable biocatalytic platforms for α-amylase immobilization: From ionic microenvironment...

Polymer membranes with ionic domains represent a promising platform for biocatalytic systems, yet their super-acidity often restricts direct enzyme binding. In this study, the potential of commercial and laboratory-prepared Nafion membranes (Nafion1 and Nafion2) as supports for the post-immobilization of α-amylase from Bacillus licheniformis (BlAmy), used as a model enzyme, was investigated for the first time. Buffer conditioning of the membranes stabilized the ionic domains of Nafion and created a suitable microenvironment for enzyme immobilization, resulting in binding yields of 46 and 32 µg cm² and activity recoveries of 58 and 78% for BlAmy-Nafion1 and BlAmy-Nafion2, respectively. Electrostatic surface potential analysis indicated that the positively charged regions of BlAmy interact with the negatively charged sulfonate groups of Nafion. Comprehensive structural characterization using multiple instrumental techniques confirmed the successful attachment of the enzyme to the membrane. Immobilization shifted the optimum working pH of the enzyme from 5.5 to 6.5 and increased the optimum working temperature from 50 to 70 °C for both immobilized structures. BlAmy-Nafion1 and BlAmy-Nafion2 showed approximately a 3 and 8-fold higher thermal stability at 70 °C, and both immobilized membranes retained approximately 80% of their activity after 8 consecutive reuse cycles. Furthermore, biocatalysts were tested in artificial starchy wastewater treatments, and BlAmy-Nafion1 and BlAmy-Nafion2 achieved approximately 82 and 93% starch removal, respectively. Future research will focus on studies on large-scale enzymatic membrane reactors for continuous-flow treatment of real wastewater and on examining the co-immobilization of BlAmy with complementary enzymes to achieve synergistic and complete starch hydrolysis.