Porous ceramic monoliths assembled from microbeads with high specific surface area for effective biocatalysis

Abstract

Most bio-technological applications such as enzyme immobilization for biocatalysis or biosensing require highly suitable carriers that offer high accessible surface area and good liquid flow permeability at the same time. Porous monolithic adsorbents (MAds), combining large specific surface areas with high liquid flow permeabilities, are prepared in a fast and versatile two step synthesis via the ionotropic gelation route. The obtained MAds consist of 3-dimensionally assembled porous microbeads with tailorable specific surface areas up to 50 m2 g−1 after sintering. The pores inside microbeads and MAds are highly interconnected with hierarchical pore diameters between 15 nm and 105 μm. MAds permeability constants are: k1 = 6 × 10−9 m2 and k2 = 4 × 10−4 m. The obtained MAds are excellent platforms for further bio-chemical surface modifications applying established silanization protocols. We perform an amino functionalization of the MAds which is subsequently used to covalently link the model enzyme laccase to the MAds. The applied amino molecules are situated across the whole cross-sectional area of each microbead, and enzymes like laccase with a mass of approximately 70 kDa are able to completely access the intra-bead pores. The maximum effectiveness factor η is 0.90 for freshly immobilized laccase. Furthermore, laccase keeps about 85% of its activity as compared to the free enzyme in solution, and after 9 days of storage the activity is still 80%. An additional flux test confirms that the immobilized enzyme remains active under continuous flux conditions for at least 16 h.