Bioactive Covalent Organic Framework Capsules for Lactate Synthesis

Capsular covalent organic frameworks (COFs) offer unique and highly tunable spaces for enzyme immobilization. Herein, a kind of bioactive covalent organic framework (bio-COF) capsule was fabricated through a sacrificial templating method for the synthesis of lactate from pyruvate. The synthesis time of COF and the amount of enzyme were optimized during the preparation of bio-COF capsules. The enzymes were entrapped in the capsule wall with a thickness of ∼240 nm and a major pore size of ∼1.8 nm. The porous structure of bio-COF capsules ensured rapid diffusion of substrates through the capsule wall. Thereby, the bio-COF capsule retained 70% of its initial activity under reaction conditions at pH 6 and 35 °C. The confinement of the capsule wall toward enzymes remarkably improved the operational stability and organic solvent tolerance. After treatment under pH 4 and 60 °C for 120 min, the bio-COF capsules still retained the relative activities of 79 and 60%, respectively. Furthermore, the bio-COF capsules exhibited superior recyclability, retaining over 85% relative activity after 8 cycles. Our study offers a general platform for immobilizing enzymes and expands the potential application of COFs in the green biomanufacturing field.