Immobilized enzymes and cell systems: an approach to the removal of phenol and the challenges to incorporate nanoparticle-based technology

Application of electrospun chitosan-based nanofibers as immobilization matrix for biomolecules

Nanofiber meshes from electrospun chitosan, highly modified with biotin and arylazides, are well-suited for application as enzyme immobilization matrices. To test this, catalytically active biomolecules were immobilized onto photocrosslinked nanofibrous nonwovens consisting mainly of biotinylated fungal chitosan and a small amount (10 w%) of poly ethylene oxide. In this study, we show that over 10 μg eugenol oxidase per milligram dry polymer matrix can be loaded on UV-crosslinked chitosan nanofibers. We further demonstrate that bound enzyme activity can be fully retained for over 7 days of storage at ambient conditions in aqueous buffer. Samples loaded at maximum enzyme carrying capacity were tested in a custom-made plug-flow reactor system with online UV-VIS spectroscopy for activity determination. High wettability and durability of the hydrophilic chitosan support matrix enabled continuous oxidation of model substrate vanillyl alcohol into vanillin with constant turnover at flow rates of up to 0.24 L/h for over 6 h. This proves the above hypothesis and enables further application of the fibers as stacked microfluidic membranes, biosensors, or structural starting points for affinity crosslinked enzyme gels. KEY POINTS: • Biotinylated chitosan-based nanofibers retain enzymes via mild affinity interactions • Immobilized eugenol oxidase shows high activity and resists continuous washing • Nanofiber matrix material tolerated high flow rates in a continuous-flow setup.

Construction of Bio-TiO2/Algae Complex and Synergetic Mechanism of the Acceleration of Phenol Biodegradation

Microalgae have been widely employed in water pollution treatment since they are eco-friendly and economical. However, the relatively slow treatment rate and low toxic tolerance have seriously limited their utilization in numerous conditions. In light of the problems above, a novel biosynthetic titanium dioxide (bio-TiO₂ NPs)-microalgae synergetic system (Bio-TiO₂/Algae complex) has been established and adopted for phenol degradation in the study. The great biocompatibility of bio-TiO₂ NPs ensured the collaboration with microalgae, improving the phenol degradation rate by 2.27 times compared to that with single microalgae. Remarkably, this system increased the toxicity tolerance of microalgae, represented as promoted extracellular polymeric substances EPS secretion (5.79 times than single algae), and significantly reduced the levels of malondialdehyde and superoxide dismutase. The boosted phenol biodegradation with Bio-TiO₂/Algae complex may be attributed to the synergetic interaction of bio-TiO₂ NPs and microalgae, which led to the decreased bandgap, suppressed recombination rate, and accelerated electron transfer (showed as low electron transfer resistance, larger capacitance, and higher exchange current density), resulting in increased light energy utilization rate and photocatalytic rate. The results of the work provide a new understanding of the low-carbon treatment of toxic organic wastewater and lay a foundation for further remediation application.

Immobilization of enzymes for bioremediation: A future remedial and mitigating strategy

Over the years, extensive urbanization and industrialization have led to xenobiotics contamination of the environment and also posed a severe threat to human health. Although there are multiple physical and chemical techniques for xenobiotic pollutants management, bioremediation seems to be a promising technology from the environmental perspective. It is an eco-friendly and low-cost method involving the application of microbes, plants, or their enzymes to degrade xenobiotics into less toxic or non-toxic forms. Moreover, bioremediation involving enzymes has gained an advantage over microorganisms or phytoremediation due to better activity for pollutant degradation with less waste generation. However, the significant disadvantages associated with the application of enzymes are low stability (storage, pH, and temperature) as well as the low possibility of reuse as it is hard to separate from reaction media. The immobilization of enzymes without affecting their activity provides a possible solution to the problems and allows reusability by easing the process of separation with improved stability to various environmental factors. The present communication provides an overview of the importance of enzyme immobilization in bioremediation, carrier selection, and immobilization methods, as well as the pros and cons of immobilization and its prospects.

Synthesis and Comparative Studies of Glucose Oxidase Immobilized on Fe3O4 Magnetic Nanoparticles Using Different Coupling Agents

Squaric acid (SA) is a compound with potential to crosslink biomacromolecules. Although SA has become over the last years a well-known crosslinking agent as a result of its good biocompatibility, glutaraldehyde (GA), a compound with proven cytotoxicity is still one of the most used crosslinkers to develop nanomaterials. In this regard, the novelty of the present study consists in determining whether it may be possible to substitute GA with a new bifunctional and biocompatible compound, such as SA, in the process of enzyme immobilization on the surface of magnetic nanoparticles (MNPs). Thus, a direct comparison between SA- and GA-functionalized magnetic nanoparticles was realized in terms of physico-chemical properties and ability to immobilize catalytic enzymes. The optimal conditions of the synthesis of the two types of GOx-immobilized MNPs were described, thus emphasizing the difference between the two reagents. Scanning Electron Microscopy and Dynamic Light Scattering were used for size, shape and colloidal stability characterization of the pristine MNPs and of those coupled with GOx. Binding of GOx to MNPs by using GA or SA was confirmed by FT-IR spectroscopy. The stability of the immobilized and free enzyme was investigated by measuring the enzymatic activity. The study confirmed that the resulting activity of the immobilized enzyme and the optimization of enzyme immobilization depended on the type of reagent used and duration of the process. The catalytic performance of immobilized enzyme was tested, revealing that the long-term colloidal stability of SA-functionalized MNPs was superior to those prepared with GA. In conclusion, the SA-functionalized bioconjugates have a better potential as compared to the GA-modified nanosystems to be regarded as catalytic nanodevices for biomedical purposes such as biosensors.