Silica-based monoliths for enzyme catalyzed reactions in microfluidic systems with an emphasis on glucose 6-phosphate dehydrogenase and cellulase

Abstract

An efficient on-chip enzyme immobilized monolith microreactor for glucose 6-phosphate dehydrogenase and its extension to cellulase catalyzed reactions is reported. The monoliths were fabricated using the sol–gel technique, where two different silica precursors were investigated, tetraethoxysilane (TEOS) and ethylene glycol modified silane (EGMS) by determining the activity and aging of the enzymes in the gels. Subsequently catalytic reactions were conducted in continuous flow microreactors and the performance of the system was evaluated by applying various flow rates (5, 10, 15, 20μl/min). The addition of polyethylene oxide (PEO) reduced shrinkage of the gels during a period of 4days after gel preparation suggesting a strengthened gel skeleton leading to a reduced channeling within the porous structure. In the microfluidic systems, the highest conversion rates achieved were 20.0% and 28.8% at a flow rate of 5μl/min with TEOS–PEO and EGMS–PEO gels. Continuous reaction exhibited better yield than batch-wise operation using same volume/enzyme ratios which can be attributed to favorable enzyme substrate affinities. However, increase in the flow rate resulted in reduced conversion rates due to lower residence times. Consequently, the applied technique not only provided shorter preparation times but also sustained the stability of immobilized enzymes.