Laccase immobilization and surface modification of activated carbon fibers by bio-inspired poly-dopamine

In this study, we developed a new synthesis method for modifying activated carbon fibers (ACFs) by dopamine with oxidation-based self-polymerization (DA-ACFs). In addition, laccase was immobilized on the surface of unmodified ACFs (L-ACFs) and DA-ACFs (LDA-ACFs) via cross-linking after being incubated for 12 h at 5 °C. The surface composition and microstructure of the samples were characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, attenuated total reflectance Fourier-transform infrared reflection and thermo-gravimetric analysis. The optimized laccase concentration for preparing the samples was 2.0 g L(−1). The results demonstrated that the successful poly-dopamine modification increased the catalytic abilities of the ACFs in terms of biocompatibility and hydrophilicity. Compared with free laccase, the immobilized laccase exhibited significantly higher relative activity over a pH range of 3.5–6.5 and a temperature range of 30–60 °C; the thermo-stability increased, and 50% relative activity of the LDA-ACFs remained after 5 h at 55 °C. After six cycles of reuse, the relative activity of LDA-ACFs remained ≥60%, compared to 40% activity remaining for L-ACFs, and long-term storage stability was demonstrated. Moreover, the kinetic parameters (K(m)) of the two immobilized laccases were both higher than that of free laccase, whereas the maximum velocities (V(max)) were lower. These results indicate that the DA-ACFs are economical, simple, and efficient carries for enzyme immobilization, and can be suitable for further biotechnology and environmental applications.