Immobilization of biocatalysts in SBA-15 ordered mesoporous silica with cross-linked enzyme aggregates

Abstract

Naturally occurring enzymes have many advantages over synthetic catalysts as biocatalytic materials. In specific, biospecies have greater catalytic activity and are more environmentally friendly. However, the loss of enzyme stability when they are removed from physiological conditions poses a significant challenge to their widespread application. Enzyme entrapment through encapsulation in templated silica materials known as Santa Barbara acid (SBA) is a cost effective and convenient approach to retaining enzyme activity in environments that differ from the physiological state. However, once the SBA host is loaded with enzyme, leaching from the material can lead to a significant loss of activity. Previous work has demonstrated that glutaraldehyde cross-linking of the enzymes to form crosslinked enzyme aggregates (CLEA) reduces leaching. The present work investigates the novel combination of SBA-15 enzyme encapsulation and CLEA formation to generate a matrix that enables hosting of a functionally active enzyme and mitigates leaching. The Brunauer-Emmett-Teller (BET) surface area of our

material that was used to encapsulate either cytochrome b5 or pepsin was 690 ± 60 m2/g. It was demonstrated that the Pluronic P-123 templating agent was necessary to make a uniform porous structure that can be used for encapsulation. Untemplated materials, while generating high surface areas, were not structured enough to effectively load the enzyme. UV-visible spectroscopy was used to probe loading efficiency as a function of pH and encapsulation time; loading efficiency and leaching as a function of loading concentration; and glutaraldehyde concentration as a function of leaching. Encapsulation in a templated silica with post-encapsulation CLEA formation is a promising approach for generating biocatalytic materials.