Environmental and intercellular Pb2+ ions determination based on encapsulated DNAzyme in nanoscale metal-organic frameworks

Tunable metal-organic frameworks assist in catalyzing DNAzymes with amplification platforms for biomedical applications

Various binding modes of tunable metal organic frameworks (MOFs) and functional DNAzymes (Dzs) synergistically catalyze the emergence of abundant functional nanoplatforms. Given their serial variability in formation, structural designability, and functional controllability, Dzs@MOFs tend to be excellent building blocks for the precise "intelligent" manufacture of functional materials. To present a clear outline of this new field, this review systematically summarizes the progress of Dz integration into MOFs (MOFs@Dzs) through different methods, including various surface infiltration, pore encapsulation, covalent binding, and biomimetic mineralization methods. Atomic-level and time-resolved catalytic mechanisms for biosensing and imaging are made possible by the complex interplay of the distinct molecular structure of Dzs@MOF, conformational flexibility, and dynamic regulation of metal ions. Exploiting the precision of DNAzymes, MOFs@Dzs constructed a combined nanotherapy platform to guide intracellular drug synthesis, photodynamic therapy, catalytic therapy, and immunotherapy to enhance gene therapy in different ways, solving the problems of intracellular delivery inefficiency and insufficient supply of cofactors. MOFs@Dzs nanostructures have become excellent candidates for biosensing, bioimaging, amplification delivery, and targeted cancer gene therapy while emphasizing major advancements and seminal endeavors in the fields of biosensing (nucleic acid, protein, enzyme activity, small molecules, and cancer cells), biological imaging, and targeted cancer gene delivery and gene therapy. Overall, based on the results demonstrated to date, we discuss the challenges that the emerging MOFs@Dzs might encounter in practical future applications and briefly look forward to their bright prospects in other fields.

Ultralow background one-pot detection of Lead(II) using a non-enzymatic double-cycle system mediated by a hairpin-involved DNAzyme

A double-cycle system has been developed for specifically detecting trace amounts of Pb2+ by significantly decreasing the background signal. The detection involves two types of RNA cleavage reactions: one using a Pb2+-specific GR5 DNAzyme (PbDz) and the other utilizing a newly constructed 10-23 DNAzyme with two hairpins embedded in its catalytic center (hpDz). The ring-structured hpDz (c-hpDz) exhibits significantly lower activity compared to the circular 10-23 DNAzyme without hairpin structures, which plays a crucial role in reducing the background signal. When Pb2+ is present, PbDz cleaves c-hpDz to its active form, which then disconnects the molecular beacon to emit the fluorescent signal. The method allows for rapid and sensitive Pb2+ detection within 40 min for 10 fM of Pb2+ and even as short as 10 min for 100 nM of Pb2+. Additionally, visual detection is possible through the non-crosslinking assembly of Au nanoparticles. The entire process can be performed in one pot and even one step, making it highly versatile and suitable for a wide range of applications, including food safety testing and environmental monitoring.

A promising nucleic acid therapy drug: DNAzymes and its delivery system

Based on the development of nucleic acid therapeutic drugs, DNAzymes obtained through in vitro selection technology in 1994 are gradually being sought. DNAzymes are single-stranded DNA molecules with catalytic function, which specifically cleave RNA under the action of metal ions. Various in vivo and in vitro models have recently demonstrated that DNAzymes can target related genes in cancer, cardiovascular disease, bacterial and viral infection, and central nervous system disease. Compared with other nucleic acid therapy drugs, DNAzymes have gained more attention due to their excellent cutting efficiency, high stability, and low cost. Here, We first briefly reviewed the development and characteristics of DNAzymes, then discussed disease-targeting inhibition model of DNAzymes, hoping to provide new insights and ways for disease treatment. Finally, DNAzymes were still subject to some restrictions in practical applications, including low cell uptake efficiency, nuclease degradation and interference from other biological matrices. We discussed the latest delivery strategy of DNAzymes, among which lipid nanoparticles have recently received widespread attention due to the successful delivery of the COVID-19 mRNA vaccine, which provides the possibility for the subsequent clinical application of DNAzymes. In addition, the future development of DNAzymes was prospected.

DNAzyme-Based Microscale Thermophoresis Sensor

Microscale thermophoresis (MST) technology has emerged as a powerful growing method in a molecular interaction study by measuring fluorescence responses of molecules inside a capillary to infrared (IR) laser heating with the benefits of rapid ratiometric measurement, separation-free, no immobilization, and low sample consumption. Combining the advantages of RNA-cleaving DNAzymes in target recognition and enzymatic catalysis and the strength of MST technology for fluorescence signaling, here, we reported a DNAzyme-based MST method for sensitive target detection. We introduced a fluorescein terminal label at the RNA-cleaving DNAzyme, and the substrate was linked to DNAzyme together with a poly-T sequence in a unimolecular design or not conjugated with DNAzyme in a bimolecular design. The presence of the cofactor activated DNAzyme to catalytically cleave the substrate, causing molecular structure alteration and significant changes in MST signals. This DNAzyme MST sensor enabled sensitively detecting activator targets Pb²⁺ and l-histidine, with a detection limit of 49 pM Pb²⁺ and 3.9 μM l-histidine. This biosensing strategy is universal and promising for wide applications.

Dual-emissive ratiometric fluorescent nanosensor based on multi-nanomaterials for Ag+ determination in lake water

In this study, a sensitive ratiometric fluorescent nanosensor was constructed using a facile one-pot method by encapsulating carbon dots (CDs) and cadmium telluride quantum dots (CdTe QDs) into the pore cavities of a metal-organic framework (ZIF-8). In this nanosensor (CD/CdTe QD@ZIF-8), the fluorescence attributed to CdTe QDs was quenched by silver ions (Ag⁺), and the fluorescence intensity of CDs did not change. The introduction of ZIF-8 into the system can not only adsorb Ag⁺ but also easily separate CDs and CdTe QDs from the matrix. The developed CD/CdTe QD@ZIF-8 composite used as a ratiometric fluorescent probe exhibited high sensitivity and selectivity towards Ag⁺. The working linear range was 0.1-20 μM with a limit of detection (LOD) of 1.49 nM. Finally, the proposed nanosensor was applied to determine Ag⁺ in lake water with satisfactory results.

Platform Formed from ZIF-8 and DNAzyme: "Turn-On" Fluorescence Assay for Simple, High-Sensitivity, and High-Selectivity Detection of Pb2

Lead contamination has posed a potential threat to the environment and food safety, arousing extensive concern. In this work, we fabricated a novel fluorescent sensing platform based on zeolitic imidazolate framework-8 (ZIF-8) and DNAzyme for monitoring Pb²⁺ in water and fish samples. ZIF-8 was proposed as a fluorescence quencher with the advantages of simple synthesis, low cost, and high quenching efficiency. The Pb²⁺-dependent GR5 DNAzyme containing the large ssDNA loop can be adsorbed onto ZIF-8 accompanied by fluorescence quenching. Upon binding with Pb²⁺, GR5 DNAzyme was activated and cleaved, leading to the release of FAM-labeled 5-base ssDNA, which restored the fluorescence. The "turn-on" assay can detect Pb²⁺ through the one-pot procedure in the range of 0.01-10.0 nM with a detection limit of 7.1 pM. The platform is promising for on-site monitoring of Pb²⁺ owing to the excellent performance of high sensitivity, low background, strong anti-interference ability, and simple operation.

DNAzyme-Functionalized Nanomaterials: Recent Preparation, Current Applications, and Future Challenges

DNAzyme-nanomaterial bioconjugates are a popular hybrid and have received major attention for diverse biomedical applications, such as bioimaging, biosensor development, cancer therapy, and drug delivery. Therefore, significant efforts are made to develop different strategies for the preparation of inorganic and organic nanoparticles (NPs) with specific morphologies and properties. DNAzymes functionalized with metal-organic frameworks (MOFs), gold nanoparticles (AuNPs), graphene oxide (GO), and molybdenum disulfide (MoS₂ ) are introduced and summarized in detail in this review. Moreover, the focus is on representative examples of applications of DNAzyme-nanomaterials over recent years, especially in bioimaging, biosensing, phototherapy, and stimulation response delivery in living systems, with their several advantages and drawbacks. Finally, the perspective regarding the future directions of research addressing these challenges is also discussed and highlighted.