Formation and characterization of laccase : polyelectrolyte complexes and their integration in layer-by-layer assemblies for wastewater treatment

Details

Supervisors

Sophie Demoustier ; Christine Dupont

Faculty

Ecole polytechnique de Louvain

Degree label

Master [120] : ingénieur civil biomédical, à finalité spécialisée

Abstract

Water is humanity’s most vital resource. However, the growth of human activity has led to an alarming increase in untreated wastewater, contaminating soils, rivers, and other natural resources, posing a major threat to people and ecosystems. Due to water scarcity and high demand, wastewater is now seen as a potential water source, rather than just waste. This transformation from waste to resource is done by wastewater treatment, which removes most pollutants from water. This study focuses on enzymatic bioremediation, an ecological and cost-effective method that offers some advantages, including the treatment of certain pollutants that conventional methods cannot treat. However, a main drawback comes with this process. To be cost-effective and implemented on a larger scale, enzymes must be immobilized to prevent their leaching from their carrying material. In this work, we will study the immobilization of an enzyme from the oxidoreductase family, called laccase, by the Layer-by-Layer (LbL) technique. Previous work demon strated that multilayers only composed of laccase and branched polyethylenimine (bPEI) lacked (structural) stability and were not suited for developing reusable materials. Therefore, this work aims at using Protein-Polyelectrolyte Complexes (PPC) as a new building block for LbL assembly. In theory, the use of PPC instead of free enzymes allows more efficient multilayer formation and results in more stable films. For that reason, this work focuses on the creation and characteri zation of Laccase-Polyelectrolyte complexes and their integration in LbL assemblies. First, PPC were formed by mixing different amounts of laccase and poly(allylamine hydrochloride) (PAH). Complexes were detected and characterized by turbidity, zeta potential, and dynamic light scattering measurements. They exhibited different characteristics depending on the PAH/Laccase mass ratios. Not all the created complexes were suitable for LBL assembly but could be used in other applications or immobilization systems. Then the selected PPC were immobilized by LbL using poly(sodium-4-styrene sulfonate) as counter-polyion. Obtained multilayers exhibited lower initial activity than those made of free laccase. However, LbL assemblies built with complexes show a slightly higher stability than assemblies with free laccase. In conclusion, this work has led to the creation and characterization of different PPC of laccase. The results show that such complexes for multilayer formation only slightly improve stability while decreasing activity. In addition, this work highlighted a possible complexation method specific to laccase, that opens new approaches for laccase isolation.