A Spring in Performance: Silica Nanosprings Boost Enzyme Immobilization in Microfluidic Channels

Enzyme microreactors are important tools of miniaturized analytics and have promising applications in continuous biomanufacturing. A fundamental problem of their design is that plain microchannels without extensive static internals, or packings, offer limited exposed surface area for immobilizing the enzyme. To boost the immobilization in a manner broadly applicable to enzymes, we coated borosilicate microchannels with silica nanosprings and attached the enzyme, sucrose phosphorylase, via a silica-binding module genetically fused to it. We showed with confocal fluorescence microscopy that the enzyme was able to penetrate the ∼70 μm-thick nanospring layer and became distributed uniformly in it. Compared with the plain surface, the activity of immobilized enzyme was enhanced 4.5-fold upon surface coating with nanosprings and further increased up to 10-fold by modifying the surface of the nanosprings with sulfonate groups. Operational stability during continuous-flow biocatalytic synthesis of α-glucose 1-phosphate was improved by a factor of 11 when the microreactor coated with nanosprings was used. More than 85% of the initial conversion rate was retained after 840 reactor cycles performed with a single loading of enzyme. By varying the substrate flow rate, the microreactor performance was conveniently switched between steady states of quantitative product yield (50 mM) and optimum productivity (19 mM min^-1) at a lower product yield of 40%. Surface coating with silica nanosprings thus extends the possibilities for enzyme immobilization in microchannels. It effectively boosts the biocatalytic function of a microstructured reactor limited otherwise by the solid surface available for immobilizing the enzyme.