Fabrication of a silica monolith micro-bioreactor entrapping highly activated lipase by a two-step sol-gel method

Micro-bioreactors are effective for high throughput production of expensive products from small amounts of substrates. Lipases are versatile enzymes for chiral syntheses, and highly activated when immobilized in alkyl-substituted silicates by the sol-gel method. For application of the immobilized lipases to a continuous-flow system, a micro-bioreactor loaded with a macroporous silica monolith is well suited, because it can easily be integrated with a separator for optical resolution. We attempted to develop a micro-capillary bioreactor containing a silica monolith-immobilized lipase. A silica monolith without shrinkage during lyophilization of the hydrogel was first formed from a 1:4 mixture of tetramethoxysilane (TMOS) and methyltrimethoxysilane (MTMS). It was then coated with silica precipitates entrapping lipase, derived from a 1:4 mixture of TMOS and n-butyltrimethoxysilane (BTMS). As a result, the monolith treated with the BTMS-based silica entrapping lipase, exhibited approximately ten times higher esterification activity than the non-treated monolith-immobilized lipase derived from the MTMS-based silica.