A Double Hemin Bonded G-Quadruplex Embedded in Metal-Organic Frameworks for Biomimetic Cascade Reaction

Biocatalytic transformations in living cells, such as enzymatic cascades, function effectively in spatially confined microenvironments. However, mimicking enzyme catalytic cascade processes is challenging. Herein, we report a new dual-Hemin-G-quadruplex (dHemin-G4) DNAzyme with high catalytic activity over noncovalent G4/Hemin and monocovalent counterparts (G4-Hemin and Hemin-G4) by covalently linking hemin to both ends of an intramolecular G4. We use MAF-7, a hydrophilic metal-organic framework (MOF), as the protecting scaffold to integrate a biocatalytic cascade consisting of dHemin-G4 DNAzyme and glucose oxidase (GOx), by a simple and mild method with a single-step encapsulation of both enzymes. Such a MAF-7-confined cascade system shows superior activity over not only traditional G4/Hemin but also other MOFs (ZIF-8 and ZIF-90), which was mainly attributed to high-payload enzyme packaging. Notably, the introduction of hydrophilic G4 allows to avoid the accumulation of hydrophobic hemin on the surface of MAF-7, which decreases cascade biocatalytic activity. Furthermore, MAF-7 as protective coatings endowed the enzyme with excellent recyclability and good operational stability in harsh environments, including elevated temperature, urea, protease, and organic solvents, extending its practical application in biocatalysis. In addition, the incorporated enzymes can be replaced on demand to broaden the scope of catalytic substrates. Taking advantages of these features, the feasibility of dHemin-G4/GOx@MAF-7 systems for biosensing was demonstrated. This study is conducive to devise efficient and stable enzyme catalytic cascades to facilitate applications in biosensing and industrial processes.