Immobilization of laccases on mechanically ground silk fibroin nanofibers for enhanced stability

Azo dyes in textile industry effluents pose significant health and environmental risks. Laccase is an enzyme capable of degrading azo dyes, offering an environmentally friendly solution for treating textile wastewater. However, laccases need to be immobilized on specific carriers to enable effective reuse in batch reactors and continuous operation in flow-through reactors. This study employed silk fibroin nanofibers (SFNFs) obtained by mechanically grinding degummed silkworm silk as sustainable carriers to immobilize laccases through carbodiimide-mediated crosslinking. The immobilized laccases (SFNF-laccases) exhibited improved pH tolerance in the range of pH 3.0-8.0 with a smaller reduction in activity compared to free laccases (SFNF-laccases: 32.9 %, free laccases: 50.4 %). The thermal stability of immobilized laccases was also improved, showing 19, 13, and 9 % higher activities than those of free laccases at 40, 50, and 60 °C, respectively. After 8 days of storage, the activity of SFNF-laccases was 79 % of their activity immediately after immobilization, whereas free laccases retained only 29 % of their initial activity. In addition, SFNF-laccases maintained 73 % of their original operational activity in a flow-through reactor after 8 days. These results demonstrate the great potential of mechanically ground SFNFs as carriers of laccase and the resulting SFNF-laccases in industrial wastewater treatment.