3-16: Immobilization of cellulase on a silica gel substrate modified using a 3-APTES self-assembled monolayer

Abstract

Cellulase is an important but expensive catalyst for production of cellulosic ethanol. Immobilization of the enzyme would allow the catalyst to be recycled for multiple batches, significantly increasing the economics of this process. For this purpose, cellulase was immobilized onto silica gel surfaces.  Silica gel was pretreated with (3-Aminopropyl) triethoxy-silane (3-APTES), and glutaraldehyde was used as a cross-linker between cellulase layer and 3-APTES layer. Hydrolysis of carboxymethylcellulose sodium salt (CMC) solution made in pH=6 acetate buffer was used to determine the activity of both free and immobilized cellulase. Fluorescamine protein assay was utilized to determine the amount of protein in the enzyme solution. As a result, cellulase was successfully immobilized on the modified silica gel surface, and no detectable amount of enzyme was stripped off during the hydrolysis of CMC solution. The specific activity of the immobilized cellulase is 7% compared with the similar amount of free cellulase. Significant activity over multiple reuses was observed.  The seventh batch achieved 82% activity of the initial batch, and the fifteenth batch retained 31% (with little decrease through 26 cycles of reuse). It was observed that the immobilized cellulase retained 48% of its initial activity after 4 days, and 22% even after 14 days.