Efficient Biocatalytic System for Biosensing by Combining Metal–Organic Framework (MOF)-Based Nanozymes and G-Quadruplex (G4)-DNAzymes

Abstract

A high catalytic efficiency associated to a robust chemical structure are among the ultimate goals when developing new biocatalytic systems for biosensing applications. To get ever closer to these goals, we report here on a combination of metal-organic framework (MOF)-based nanozymes and G-quadruplex (G4)-based catalytic system known as G4-DNAzyme. This approach aims at combining the advantages of both partners (chiefly, the robustness of the former, the modularity of the latter). To this end, we used MIL-53(Fe) MOF and linked it covalently to a G4-forming sequence (F3TC), itself covalently linked to its cofactor hemin. The resulting complex (referred to as MIL-53(Fe)/G4-hemin) exhibited exquisite peroxidase-mimicking oxidation activity and an excellent robustness (being stored in water for weeks). These properties were exploited to devise a new biosensing system, based on a cascade of reactions catalyzed by the nanozyme (ABTS oxidation) and an enzyme, the alkaline phosphatase (or ALP, ascorbic acid 2-phosphate dephosphorylation). The product of the latter poisoning the former, we thus designed a biosensor for ALP (a marker of bone diseases and cancers), with a very low limit of detection (LOD, 0.02 U L -1 ) which is operative in human plasma samples.

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

“…It is well-known that hydrophobic hemin possesses low catalytic activity in aqueous solution due to dimerization, and the introduction of G4 can form a noncovalent G4/hemin DNAzyme system with HRP-like activity. , Recently, our group reported that covalently anchored hemin at the 3-terminal of G4 was more active than the previous nonconjugated system, , which stimulated us to test whether covalent attachment of hemin to both ends of G4 (3′- and 5′-terminal, denoted as dHemin-G4) would further improve the peroxidase activity of the system. As expected, the catalytic activity of the dHemin-G4 DNAzyme system coupled with hemin at both ends of G4 was significantly higher than that of noncovalent G4/hemin and also was 182 times higher than that of hemin.…”

“…The preparation method of double hemin covalently connected to the both ends of G4 DNA sequence, 5′-CTG­GGT­GGG­TGG­GTG­GGTC-3′, that is, dHemin-G4, was based on a reported method of construction of single covalent linkage of G4 and hemin with minor modifications . Specifically, 1 mL of hemin DMSO solution (1 mM) was mixed with 0.5 mL of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) and N -hydroxysuccinimide (NHS) solution (10 mM each) followed by stirring for 2 h at room temperature to activate the carboxyl group of hemin.…”

“…Cascade biocatalysis, an important class of chemical transformation, is significant for biological signal transduction and metabolic pathways by providing sequential intercommunication and instant signal feedback in cellular environments. − Unsurprisingly, mimicking enzyme biocatalytic cascades for the construction of complex chemical transformation networks is receiving increasing concerns. ,− Among them, glucose oxidase (GOx) and horseradish peroxidase (HRP) constitute a typical cascade reaction system, which has been widely used in bioanalysis. − Recent efforts have been devoted to developing economical and robust HRP substitutes, such as nanozymes and DNAzymes. − Interestingly, hemin is an inexpensive and promising substitute of HRP, usually obtained from the active center of hemin-containing enzymes. , Unfortunately, hemin is a hydrophobic small molecule and shows low catalytic activity in aqueous media owing to its poor aqueous solubility and molecular aggregation . To increase the catalytic activity and aqueous stability of hemin, several strategies have been proposed by modification of nanomaterials (i.e., graphene and MOFs) and anchoring to the biological macromolecules (i.e., protein, polypeptide, and G-quadruplex). − …”

“…10 –7 M) compared with HRP, , which needs to be improved. Recently, our group reported an efficient system in which hemin covalently linked to the 3′-terminal of G4 can obviously enhance its catalytic activity and reduce the background signal, showing a clear advantage over nonconjugated G4/hemin. , Encouraged by the efficient catalytic performance of the conjugated G4-hemin system, we sought to explore higher catalytic activity than that of reported covalent G4-hemin system by covalent integration of hemin at both 3′- and 5′- ends of G4, denoted as dHemin-G4 DNAzyme, which has not been reported previously.…”

Duplex-Specific Nuclease-Enabled Target Recycling on Semiconducting Metal–Organic Framework Heterojunctions for Energy-Transfer-Based Organic Photoelectrochemical Transistor miRNA Biosensing

“…Metal–organic frameworks (MOFs) are an interesting family of hybrid porous polymeric materials assembled by the coordination of metal ions and organic linkers. − MOFs have drawn tremendous interdisciplinary interest because of their multiple desirable characteristics, e.g., ultrahigh porosity, tunable pore size, high surface area, adjustable structure, and composition as well as functional diversity. − Among numerous MOFs, semiconductor MOFs, e.g., MOF-5, MIL-100­(Fe), UiO-66­(Zr), MIL-125­(Ti), and porphyrinic MOFs, are of particular interest due to their light-harvesting properties. Currently, various semiconductor MOFs and their functional heterojunctions have been explored as advanced materials for specific biomedical applications. − Although a promising perspective has been revealed, the full potential of semiconductor MOFs remains largely untapped, especially research concerning their application in bioelectronics and optoelectronics is quite scarce.…”