Intracellular miRNA Imaging Based on a Self-Powered and Self-Feedback Entropy-Driven Catalyst-DNAzyme Circuit

A rolling circle amplification-based DNAzyme walker against intracellular degradation for imaging tumor cells' microRNA

We present a novel DNA molecular machine (RCA-D-Walker) that integrates a DNAzyme-based molecular beacon with RCA-based vectors for miRNA imaging in tumor cells. It can accurately target tumor cells through the sgc8 aptamer. The target miRNA can restore the DNAzyme's ability to cleave the substrate, which in turn produces an amplified fluorescent signal. The RCA-D-Walker exhibits enhanced tumor cell targeting, improved cell permeability, and greater resistance to nuclease degradation. Utilizing this strategy, we achieved accurate and efficient imaging of miRNA-21 in tumor cells.

A portability self-powered sensor facilitates sensitive Cd2+ detection: Dual mechanism and three quantitative mode

As a common heavy metal contaminant, Cd2+ has adverse effects on food safety and consumer health. It is very important for human health to realize highly sensitive Cd2+ detection methods. The self-powered sensing system based on enzyme biofuel cells (EBFCs) does not need an external power supply, which can simplify the experimental equipment and has great application value in portable detection. Thus, the biosensor is innovatively integrated into the screen-printed electrode to construct a new type of portable sensor suitable for on-site and real-time Cd2+ detection. Hybridization chain reaction (HCR) combined with the Cd2+-dependent deoxyribose (DNAzyme) signal amplification strategy is used to enhance the detection sensitivity while specifically recognizing the Cd2+. Moreover, the self-powered sensor combines with smartphones to realize quantitative Cd2+ detection without other instruments and has the characteristic of Effectively improving the hazard detection technology is essential to ensure food safety. Portability, simplicity, and speed are suitable for real-time Cd2+ detection in the field. The dual mechanism and three quantitative modes combining colorimetric and two electrical signals output modes are adopted to realize the visualization and accurate detection. A series of research results confirm that this strategy is of great significance to strengthen the development of intelligent Cd2+ technology, expand the application of self-powered sensing technology, and improve the safety detection system.

Recent Advances in DNA-Based Nanoprobes for In vivo MiRNA Imaging

As a post transcriptional regulator of gene expression, microRNAs (miRNA) is closely related to many major human diseases, especially cancer. Therefore, its precise detection is very important for disease diagnosis and treatment. With the advancement of fluorescent dye and imaging technology, the focus has shifted from in vitro miRNA detection to in vivo miRNA imaging. This concept review summarizes signal amplification strategies including DNAzyme catalytic reaction, hybrid chain reaction (HCR), catalytic hairpin assembly (CHA) to enhance detection signal of lowly expressed miRNAs; external stimuli of ultraviolet (UV) light or near-infrared region (NIR) light, and internal stimuli such as adenosine triphosphate (ATP), glutathione (GSH), protease and cell membrane protein to prevent nonspecific activation for the avoidance of false positive signal; and the development of fluorescent probes with emission in NIR for in vivo miRNA imaging; as well as rare earth nanoparticle based the second near-infrared window (NIR-II) nanoprobes with excellent tissue penetration and depth for in vivo miRNA imaging. The concept review also indicated current challenges for in vivo miRNA imaging including the dynamic monitoring of miRNA expression change and simultaneous in vivo imaging of multiple miRNAs.

Autocatalytic DNA circuitries

Autocatalysis, a self-sustained replication process where at least one of the products functions as a catalyst, plays a pivotal role in life's evolution, from genome duplication to the emergence of autocatalytic subnetworks in cell division and metabolism. Leveraging their programmability, controllability, and rich functionalities, DNA molecules have become a cornerstone for engineering autocatalytic circuits, driving diverse technological applications. In this tutorial review, we offer a comprehensive survey of recent advances in engineering autocatalytic DNA circuits and their practical implementations. We delve into the fundamental principles underlying the construction of these circuits, highlighting their reliance on DNAzyme biocatalysis, enzymatic catalysis, and dynamic hybridization assembly. The discussed autocatalytic DNA circuitry techniques have revolutionized ultrasensitive sensing of biologically significant molecules, encompassing genomic DNAs, RNAs, viruses, and proteins. Furthermore, the amplicons produced by these circuits serve as building blocks for higher-order DNA nanostructures, facilitating biomimetic behaviors such as high-performance intracellular bioimaging and precise algorithmic assembly. We summarize these applications and extensively address the current challenges, potential solutions, and future trajectories of autocatalytic DNA circuits. This review promises novel insights into the advancement and practical utilization of autocatalytic DNA circuits across bioanalysis, biomedicine, and biomimetics.

DNA domino circuits based on a hairpin exonuclease assistance signal transmission architecture for temporal logic operations

DNA circuits are important fundamental tools for performing temporal logic operations with complex structures, but they lack sequence orthogonality. Here, we developed a simple and orthogonal hairpin exonuclease assistance signal (H-EAST) architecture to construct DNA domino circuits with time-delay characteristics and temporal logic operations, which has potential applications in biomolecular computing.

Facile, green and scalable synthesis of single-layer manganese dioxide nanosheets and its application for GSH and cTnI colorimetric detection

Manganese dioxide (MnO2) nanosheets possess unique physical and chemical properties, making them widely applicable in various fields, such as chemistry and biomedicine. Although MnO2 nanosheets are produced using bottom-up wet chemistry synthesis methods, their scale is below the gram level and requires a long processing time, restricting their effective scale-up from laboratory to market. We report a facile, green and scalable synthesis of MnO2 nanosheets by mixing Shiranui mandarin orange juice and KMnO4 for 30 minutes. We produced more than one gram (1.095) of MnO2 nanosheets with a 0.65 nm mean thickness and a 50 nm mean lateral size. Furthermore, we established a visual colorimetric biosensing strategy based on MnO2 nanosheets for the assay of glutathione (GSH) and cardiac troponin I (cTnI), offering high sensitivity and feasibility in clinical samples. For GSH, the limit of detection was 0.08 nM, and for cTnI, it was 0.70 pg mL-1. Meanwhile, the strategy can be used for real-time analysis by applying a smartphone-enabled biosensing strategy, which can provide point-of-care testing in remote areas.

A cancer-targeted glutathione-gated probe for self-sufficient ST/CDT combination therapy and FRET-based miRNA imaging

A cancer-targeted glutathione (GSH)-gated theranostic probe (CGT probe) for intracellular miRNA imaging and combined treatment of self-sufficient starvation therapy (ST) and chemodynamic therapy (CDT) was developed. The CGT probe is constructed using MnO2 nanosheet (MS) as carrier material to adsorb the elaborately designed functional DNAs. It can be internalized by cancer cells via specific recognition between the AS1411 aptamer and nucleolin. After CGT probe entering the cancer cells, the overexpressed GSH, as gate-control, can degrade MS to Mn2+ which can be used for CDT by Fenton-like reaction. Simultaneously, Mn2+-mediated CDT can further cascade with the enzyme-like activities (catalase-like activity and glucose oxidase-like activity) of CGT probe, achieving self-sufficient ST/CDT synergistic therapy. Meanwhile, the anchored DNAs are released, achieving in situ signal amplification via disubstituted-catalytic hairpin assembly (DCHA) and FRET (fluorescence resonance energy transfer) imaging of miR-21. The in vitro and in vivo experiments demonstrated that accurate and sensitive miRNA detection can be achieved using the CGT probe. Overall, the ingenious CGT probe opens a new avenue for the development of early clinical diagnosis and cancer therapy.

A two-layer circuit cascade-based DNA machine for highly sensitive miRNA imaging in living cells

Sensitive detection of microRNA (miRNA), one of the most promising biomarkers, plays crucial roles in cancer diagnosis. However, the low expression level of miRNA makes it extremely urgent to develop ultrasensitive and highly selective strategies for quantification of miRNA. Herein, a DNA machine is rationally constructed for amplified detection and imaging of low-abundance miRNA in living cells based on the toehold-mediated strand displacement reaction (TMSDR). The isothermal and enzyme-free DNA machine with low background leakage is fabricated by integrating two DNA circuits into a cascade system, in which the output of one circuit serves as the input of the other one. Once the DNA machine is transfected into breast cancer cells, the overexpressed miRNA-203 initiates the first-layer circuit through TMSDR, leading to the concentration variation of fuel strands, which further influences the assembly of hairpin DNA in the second-layer circuit and the occurrence of fluorescence resonance energy transfer (FRET) for fluorescence imaging. Benefiting from the cascade of the two-layer amplification reaction, the proposed DNA machine acquires a detection limit down to 4 fM for quantification of miR-203 and a 10 000-fold improvement in amplification efficiency over the single circuit. Therefore, the two-layer circuit cascade-based DNA machine provides an effective platform for amplified analysis of low-abundance miRNA with high sensitivity, which holds great promise in biomedical and clinical research.

Programmable Entropy-Driven Circuit-Cascaded Self-Feedback DNAzyme Network for Ultra-Sensitive Fluorescence and Photoelectrochemical Dual-Mode Biosensing

Inspired by natural DNA networks, programmable artificial DNA networks have become an attractive tool for developing high-performance biosensors. However, there is still a lot of room for expansion in terms of sensitivity, atom economy, and result self-validation for current microRNA sensors. In this protocol, miRNA-122 as a target model, an ultrasensitive fluorescence (FL) and photoelectrochemical (PEC) dual-mode biosensing platform is developed using a programmable entropy-driven circuit (EDC) cascaded self-feedback DNAzyme network. The well-designed EDC realizes full utilization of the DNA strands and improves the atomic economy of the signal amplification system. The unique and rational design of the double-CdSe quantum-dot-released EDC substrate and the cascaded self-feedback DNAzyme amplification network significantly avoids high background signals and enhances sensitivity and specificity. Also, the enzyme-free, programmable EDC cascaded DNAzyme network effectively avoids the risk of signal leakage and enhances the accuracy of the sensor. Moreover, the introduction of superparamagnetic Fe3O4@SiO2-cDNA accelerates the rapid extraction of E2-CdSe QDs and E3-CdSe QDs, which greatly improves the timeliness of sensor signal reading. In addition to the strengths of linear range (6 orders of magnitude) and stability, the biosensor design with dual signal reading makes the test results self-confirming.

Catalytic hairpin assembly triggering amplified DNAzyme-feedback for sensitive detection of hepatitis C virus genotype 1b

Developing a simple, reliable, and sensitive hepatitis C virus (HCV) genetic sensing platform is of great significance for diagnosing diseases and selecting appropriate antiviral treatments. Herein, a tandem nucleic acid amplification strategy for sensitive detection of HCV genotype 1b (HCV-1b) was developed by stringing the catalytic hairpin assembly (CHA) and the triggered DNAzyme amplifier. The hairpin reactants were initiated by the target to produce lots of triggering double-stranded DNA sequences which can efficiently activate the subsequent blocked DNAzyme. Thereby, the continuous cleavage of substrate was realized, resulting in the fluorescence signal amplification. The DNA-based isothermal CHA-DNAzyme (CDz) sensing platform was successfully applied for sensitive detection of HCV-1b with the limit of detection (84 pM) and showed good selectivity. Moreover, the practical detection of target DNA in the complex biologic matrix indicated that the developing strategy had good potential for early HCV infection diagnosis.

Hybridization chain reaction assisted multicolor immunosensor for sensitively detection of human chorionic gonadotropin

The level of human chorionic gonadotropin (HCG) is an important indicator for early pregnancy, pregnancy-related diseases trophoblastic diseases and even cancer diagnosis. Therefore, sensitive detection of HCG has crucial significance in clinical, especially in gynaecology and obstetrics. Herein, a hybridization chain reaction (HCR) assisted multicolor immunosensor have been developed for HCG analysis. The proposed method introduced HCR after the immunoreaction between antibody and HCG protein, and produced long double strand DNA (dsDNA) that contain biotin sites. The streptavidin-horseradish peroxidase was linked on the dsDNA by the interaction between biotin and streptavidin, and can further mediated gold nanobipyramids (Au NBPs) etching. The localized surface plasmon resonance absorption peaks of Au NBPs blue shift and accompanied a vivid color change after etching effect. Based on this color change, HCG could be qualitative and semi-quantitative detected. Because of the introduction of HCR and enzyme amplification technique, the proposed method exhibited high sensitivity with a linear range of 0.1-2000 pg/mL and limit of detection (LOD) of 0.1 pg/mL. Finally, the proposed immunosensor was used to detect clinical serum samples. The results show there are no significant differences between clinical results and the test results by this method, indicating the practicability of the proposed method.

Catalytic Assembly of DNAzyme Integrates with Primer Exchange Reaction (CDiPER) for Highly Sensitive Detection of MicroRNA

MicroRNAs (miRNAs) have significant regulatory functions in the modulation of gene expression, making them essential biomarkers for the diagnosis and prognosis of diseases. Nevertheless, the identification of miRNA poses significant difficulty in terms of its low abundance, necessitating sensitive and reliable approaches. Herein, we develop a simple approach, termed Catalytic assembly of DNAzyme integrates with Primer Exchange Reaction (CDiPER), for reliable and sensitive miRNA detection through the target recognition-triggered DNAzyme assembly and primer exchange reaction (PER) strategy. In this method, target miRNA can precisely bind with a specifically designed hairpin probe (H probe) to induce the conformation changes of the H probe, releasing DNAzyme sections to activate the PER process for signal amplification and fluorescence signal production. The established method displays a high dynamic range of over 6 orders of magnitude and a low detection limit of 312 aM. The created method has a number of unique advantages, such as (i) a better sensitivity than existing systems using PER for signal amplification as a result of its integration with the target recognition-triggered DNAzyme assembly and (ii) streamlined operating procedures. Further, the technology was used to detect the expression of miRNA in collected clinical samples from diabetes mellitus patients, revealing that miRNA was decreased in patients and demonstrating the significant clinical promise of the method.

Orthogonally Sequential Activation of Self-Powered DNAzymes Cascade for Reliable Monitoring of mRNA in Living Cells

Ratiometric imaging of tumor-related mRNA is significant, yet spatiotemporally resolved regulation on the ratiometric signals to avoid non-specific activation in the living cells remains challenging. Herein, orthogonally sequential activation of concatenated DNAzyme circuits is, first, developed for Spatio Temporally regulated Amplified and Ratiometric (STAR) imaging of TK1 mRNA inside living cells with enhanced reliability and accuracy. By virtue of the synthesized CuO/MnO2 nanosheets, orthogonally regulated self-powered DNAzyme circuits are operated precisely in living cells, sequentially activating two-layered DNAzyme cleavage reactions to achieve the two ratiometric signal readouts successively for reliable monitoring of low-abundance mRNA in living cells. It is found that the ratiometric signals can only be derived from mRNA over-expressed tumor cells, also irrespective of probes' delivery concentration. The presented approach could provide new insight into orthogonally regulated ratiometric systems for reliable imaging of specific biomarkers in living cells, benefiting disease precision diagnostics.

High-fidelity intracellular imaging of multiple miRNAs via stimulus-responsive nanocarriers and catalytic hairpin assembly

An advanced nanoplatform was developed by integrating catalytic hairpin assembly (CHA) with glutathione-responsive nanocarriers, enabling superior imaging of dual cancer-related miRNAs. Two distinct CHA circuits for the sensing of miRNA-21 and miRNA-155 were functionalized on biodegraded MnO2. In the presence of GSH and the corresponding miRNAs, the degraded MnO2 released the DNA cargos, activating the CHA circuits and recovering the fluorescence. This approach offers a reliable sensing performance with highly selective cell-identification capacity, positioning it as a pivotal tool for imaging multiple biomarkers in living cells.

Stimuli-responsive probes for amplification-based imaging of miRNAs in living cells

MicroRNAs (miRNAs) have emerged as important biomarkers in biomedicine and bioimaging due to their roles in various physiological and pathological processes. Real-time and in situ monitoring of dynamic fluctuation of miRNAs in living cells is crucial for understanding these processes. However, current miRNA imaging probes still have some limitations, including the lack of effective amplification methods for low abundance miRNAs bioanalysis and uncontrollable activation, leading to background signals and potential false-positive results. Therefore, researchers have been integrating activatable devices with miRNA amplification techniques to design stimuli-responsive nanoprobes for "on-demand" and precise imaging of miRNAs in living cells. In this review, we summarize recent advances of stimuli-responsive probes for the amplification-based imaging of miRNAs in living cells and discuss the future challenges and opportunities in this field, aiming to provide valuable insights for accurate disease diagnosis and monitoring.

Concatenated dynamic DNA network modulated SERS aptasensor based on gold-magnetic nanochains and Au@Ag nanoparticles for enzyme-free amplification analysis of tetracycline

Tetracycline (TC) poses a great threat to food and environmental safety due to its misuse in animal husbandry and aquaculture. Therefore, an efficient analytical method is needed for the detection of TC to prevent possible hazards. Herein, a cascade amplification SERS aptasensor for sensitive determination of TC was constructed based on aptamer, enzyme-free DNA circuits, and SERS technology. The capture probe and signal probe were obtained by binding DNA hairpins H1 and H2 to the prepared Fe₃O₄@hollow-TiO₂/Au nanochains (Fe₃O₄@h-TiO₂/Au NCs) and Au@4-MBA@Ag nanoparticles, respectively. The dual amplification of EDC-CHA circuits significantly facilitated the sensitivity of the aptasensor. Additionally, the introduction of Fe₃O₄ simplified the operation of the sensing platform due to its superb magnetic capability. Under optimal conditions, the developed aptasensor exhibited a distinct linear response to TC with a low limit of detection of 15.91 pg mL^-1. Furthermore, the proposed cascaded amplification sensing strategy exhibited excellent specificity and storage stability, and its practicability and reliability were verified by TC detection of real samples. This study provides a promising idea for the development of specific and sensitive signal amplification analysis platforms in the field of food safety.

A Smart Deoxyribozyme-Programmable Catalytic DNA Circuit for High-Contrast MicroRNA Imaging

Synthetic catalytic DNA circuits have been recognized as a promising signal amplification toolbox for sensitive intracellular imaging, yet their selectivity and efficiency are always constrained by uncontrolled off-site signal leakage and inefficient on-site circuitry activation. Thus, the endogenously controllable on-site exposure/activation of DNA circuits is highly desirable for achieving the selective imaging of live cells. Herein, an endogenously activated DNAzyme strategy was facilely integrated with a catalytic DNA circuit for guiding the selective and efficient microRNA imaging in vivo. To prevent the off-site activation, the circuitry constitute was initially caged without sensing functions, which could be selectively liberated by DNAzyme amplifier to guarantee the high-contrast microRNA imaging in target cells. This intelligent on-site modulation strategy can tremendously expand these molecularly engineered circuits in biological systems.

A Smart Metal-Polyphenol-DNAzyme nanoplatform for Gene-Chemodynamic Synergistic Tumor therapy

DNAzyme-based gene regulation shows great potential for the therapy of many cancers. However, ineffective delivery and insufficient cofactor supply pose challenges for potent gene therapy. In this study, we constructed a smart metal-polyphenol-DNAzyme nanoplatform (TA-Mn@Dz NPs) with intrinsic stability, effective delivery, and cofactor self-supply ability for gene-chemodynamic synergistic tumor therapy. Tannic acid, a plant-derived polyphenol, acts as an intermediate structural unit to mediate the assembly of Mn²⁺/DNAzyme and tumor acid environment-responsive nanocarriers. Intracellularly, the acidic environment triggers the decomposition of TA-Mn@Dz NPs to release DNAzyme and Mn²⁺. The Mn²⁺ ion not only boosts the catalytic cleavage of surviving mRNA for effective gene therapy but also activates chemodynamic therapy (CDT), generating highly toxic ·OH from endogenous H₂O₂. When tail intravenously injected into MCF-7 tumor-bearing mice, the TA-Mn@Dz NPs display desirable synergistic gene-chemodynamic antitumor effects, paving the way for developing DNAzyme-based multifunctional theranostic platforms for biomedical applications. STATEMENT OF SIGNIFICANCE: 1. A smart metal-polyphenol-DNAzyme nanoplatform was constructed for gene-chemodynamic synergistic tumor therapy. 2. Tannic acid act as intermediate structural units to mediate the assembly of Mn²⁺/DNAzyme and tumor acid environment-responsive nanocarriers. 3. The Mn²⁺-ion could not only boost the catalytic cleavage of surviving mRNA for effective gene therapy, but also catalyze endogenous H₂O₂ to form cytotoxic hydroxyl radicals for chemodynamic therapy. 4. Our work paves an extremely simple way to integrate gene therapy with CDT for the dual-catalytic tumor treatment.

Compute-and-Release Logic-Gated DNA Cascade Circuit for Accurate Cancer Cell Imaging

Accurate identification of cancer cells is an essential prerequisite for cancer diagnosis and subsequent effective curative interventions. The logic-gate-assisted cancer imaging system that allows a comparison of expression levels between biomarkers, rather than just reading biomarkers as inputs, returns a more comprehensive logical output, improving its accuracy for cell identification. To fulfill this key criterion, we develop a compute-and-release logic-gated double-amplified DNA cascade circuit. This novel system, CAR-CHA-HCR, consists of a compute-and-release (CAR) logic gate, a double-amplified DNA cascade circuit (termed CHA-HCR), and a MnO₂ nanocarrier. CAR-CHA-HCR, a novel adaptive logic system, is designed to logically output the fluorescence signals after computing the expression levels of intracellular miR-21 and miR-892b. Only when miR-21 is present and its expression level is above the threshold C_miR-21 > C_miR-892b, the CAR-CHA-HCR circuit performs a compute-and-release operation on free miR-21, thereby outputting enhanced fluorescence signals to accurately image positive cells. It is capable of comparing the relative concentrations of two biomarkers while sensing them, thus allowing accurate identification of positive cancer cells, even in mixed cell populations. Such an intelligent system provides an avenue for highly accurate cancer imaging and is potentially envisioned to perform more complex tasks in biomedical studies.

Programmable DNA Circuit-Facilitated Determination of Circulating Extracellular Vesicle PD-L1 for Lung Cancer Diagnosis and Immunotherapy Response Prediction

Circulating extracellular vesicle (EV) PD-L1 is correlated with the occurrence and progression of lung cancer and has great potential as a valuable diagnostic and immunotherapy predictive biomarker. In this work, we propose a fluorescent biosensing method for the sensitive and accurate determination of circulating EV PD-L1. Specifically, after the phosphatidylserine-targeting peptide-assisted magnetic enrichment, a programmable DNA circuit is designed to translate the presence of PD-L1 to the appearance of numerous duplex DNA probes on the circulating EV surface. Upon fructose treatment, these newly formed duplex DNA probes are released from the EV surface to activate the trans-cleavage activity of CRISPR/Cas12a system, which finally produces a significant fluorescence signal. Experimental results reveal that the method not only enables sensitive determination of EV PD-L1 with a detection limit of 67 particles/mL but also demonstrates the potential use in the diagnosis and immunotherapy response prediction of lung cancer in a principle-of-proof study. Therefore, the method may provide a useful tool for EV PD-L1 determination, which may provide valuable information for the precise diagnosis and personalized treatment of lung cancer patients.

Ultrasonic-controlled "explosive" hydrogels to precisely regulate spatiotemporal osteoimmune disturbance

Spatiotemporal Immune disorder is a key factor leading to the failure of bone tissue healing. It is of vital importance to accurately suppress excessive peak immune response within 24-48 h of the injury and so regulate the spatiotemporal osteoimmune disturbance of bones. In this study, Ultrasound Controlled "Explosive" (UCE) hydrogels were prepared from gelatin-hyaluronic acid methacrylate hydrogels loaded with resveratrol nanobubbles produced by double emulsification through a condensation reaction. Such materials innovatively enable ultrasound-controlled RES release for precise regulation of spatiotemporal osteoimmune disorders. Under an ultrasonic power level of 1.5 W/cm², the rate of effectively released RES through the blast of UCE hydrogels reached 38.14 %. And compared with the control group, the in vivo inhibition of inflammation and osteogenesis effects of UCE hydrogels were more effective, respectively. As suggested by the results, the excessive local inflammatory response was inhibited by the release of resveratrol, the temporospatial disorder of bone immune was precisely regulated, and as a result, the process of bone repair was accelerated. Altogether, this study confirms that the newly created UCE Hydrogels effectively promote bone repair by intervening peak inflammation during the early phase of fracture healing.

High-fidelity imaging of intracellular microRNA via a bioorthogonal nanoprobe

The spatiotemporal visualization of intracellular microRNA (miRNA) plays a critical role in the diagnosis and treatment of malignant disease. Although DNAzyme-based biosensing has been regarded as the most promising candidate, inefficient analytical resolution is frequently encountered. Here, we propose a bioorthogonal approach toward high-fidelity imaging of intracellular miRNA by designing a multifunctional nanoprobe that integrates MnO₂ nanosheet-mediated intracellular delivery and activation by a fat mass and obesity-associated protein (FTO)-switched positive feedback. MnO₂ nanosheets facilitate nanoprobe delivery and intracellular DNAzyme cofactors are released upon glutathione-triggered reduction. Meanwhile, an m6A-caged DNAzyme probe could be bioorthogonally activated by intracellular FTO to eliminate potential off-target activation. Therefore, the activated DNAzyme probe and substrate probe could recognize miRNA to perform cascade signal amplification in the initiation of the release of Mn²⁺ from MnO₂ nanosheets. This strategy realized high-fidelity imaging of intracellular aberrant miRNA within tumor cells with a satisfactory detection limit of 9.7 pM, paving the way to facilitate clinical tumor diagnosis and prognosis monitoring.

An enzyme-powered microRNA discriminator for the subtype-specific diagnosis of breast cancer

Breast cancer, a disease with highly heterogeneous features, is the most common malignancy diagnosed in people worldwide. Early diagnosis of breast cancer is crucial for improving its cure rate, and accurate classification of the subtype-specific features is essential to precisely treat the disease. An enzyme-powered microRNA (miRNA, RNA = ribonucleic acid) discriminator was developed to selectively distinguish breast cancer cells from normal cells and further identify subtype-specific features. Specifically, miR-21 was used as a universal biomarker to discriminate between breast cancer cells and normal cells, and miR-210 was used to identify triple-negative subtype features. The experimental results demonstrated that the enzyme-powered miRNA discriminator displayed low limits of detection at fM levels for both miR-21 and miR-210. Moreover, the miRNA discriminator enabled the discrimination and quantitative determination of breast cancer cells derived from different subtypes based on their miR-21 levels, and the further identification of the triple-negative subtype in combination with the miR-210 levels. Therefore, it is hoped that this study will provide insight into subtype-specific miRNA profiling, which may have potential use in the clinical management of breast tumours based on their subtype characteristics.