Congo red decolorization by immobilized laccase through chitosan nanoparticles on the glass beads

Laccase, the blue oxidase enzyme with high potency in green synthesis and biodegradation of phenolic compounds, was immobilized by means of chitosan nanoparticles (CS-NPs) on the surface of activated glass beads. Decolorization of Congo red, a harmful industrial dye, was accomplished with nanoparticulated immobilized laccase, directly attaching enzyme on the surface of the glass beads, as well as the free enzyme in order to assess the decolorization activity of immobilized and non-immobilized laccase. Glass surface functionalization was achieved by using chemicals such as sodium hydroxide, 3-aminopropyltriethoxysilane (APES), and glutaraldehyde. Dynamic light scattering (DLS) and scanning electron microscopy (SEM) were used for characterizing enzyme-associated CS-NPs, made by the ion gelation method. Fourier Transform Infrared Spectroscopy (FT-IR) was carried out to identify the attached chemical groups on the surface of the glass beads. Immobilization yields for nanoparticulated and non-nanoparticulated enzymes were 75 ± 4.2 and 68.6 ± 6.4%, respectively whereas, immobilization efficiency for nanoparticulated and non-nanoparticulated laccases were calculated as 40.1 ± 3.4 and 32.2 ± 7.5%, respectively. The applied method for immobilization resulted in increased thermal stability, reusability, and lifetime of the enzyme. Thermal stability of the nanoparticulated immobilized enzyme increased up to near boiling temperature. In addition, 98% of initial decolorization activity of the nanoparticulated immobilized enzyme was retained after 25 successive cycles.

► Laccase was immobilized by chitosan nanoparticles on the activated glass beads.
► CS-NPs were applied for decolorization of Congo red, a harmful industrial dye.
► Thermal stability of the nanoparticulated immobilized enzyme was increased to 95 °C.
► The reusability was determined for 25 rounds by decreasing by less than 4%.