A fluorescent microarray platform based on catalytic hairpin assembly for MicroRNAs detection

A target-triggered colorimetric sensor for ultrasensitive detection of miRNAs based on self-powered three-dimensional DNA walker

MicroRNAs (miRNAs) play an important role in the process of heart failure (HF) and are emerging biomarkers that can be used for the auxiliary diagnosis of HF. However, it is very challenging to accurately analyze the expression levels of trace miRNAs in complex clinical samples. Here, we developed an enzyme-free colorimetric sensor for the ultrasensitive detection of miRNA-423-5p (HF-associated miRNA) based on three-dimensional DNA walkers constructed from functional nucleic acids and gold nanoparticles (AuNPs). DNAzyme with cleavage activity was specifically activated by miRNA-423-5p to sustainably cleave the substrate, thereby releasing the trigger sequence to initiate the subsequent mismatched catalytic hairpin assembly (MCHA) cycle. Then, as the MCHA cycle proceeded to continuously expose the G-quadruplex (GQ) sequence, the sequence bound with hemin to form a large amount of GQ/hemin DNAzyme on the surface of the AuNPs, which rapidly catalyzed the chromogenic oxidation of 3,3',5,5'-tetramethylbenzidine to yield an amplified colorimetric signal readout. The colorimetric sensor exhibited an ultralow detection limit (32 fM), showed excellent specificity and performed well in serum samples. The sensor was applied to detect miRNA-423-5p in clinical plasma samples from healthy individuals and HF patients, and the results revealed its good clinical application in HF diagnosis. Thus, the developed colorimetric sensor provides a convenient detection tool for early screening and diagnosis of HF, as well as for pathophysiological studies.

Label-free fluorescent biosensor based on AuNPs etching releasing signal for miRNA-155 detection

Quantitative microRNA (miRNA) detection is crucial for early breast cancer diagnosis and prognosis. However, quick and stable fluorescence sensing for miRNA identification is still challenging. This work developed a novel label-free detection method based on AuNPs etching for quantitatively detecting miRNA-155. A layer of AuNPs was grown on the surface of mesoporous silica nanoparticles (MSN) loaded with Rhodamine 6G (R6G) using seed-mediated growth, followed by probe attachment. In the presence of miRNA-155, the MSN@R6G@AuNP surface loses the protection of the attached probe, rendering AuNPs susceptible to etching by hydrochloric acid. This results in a significant fluorescent signal being released in the free space. The encapsulation with AuNPs effectively reduces signal leakage, while the rapid etching process shortens detection time. This strategy enables sensitive and fast detection with a detection range of 100 fM to 100 nM, a detection limit of 2.18 fM, and a detection time of 30 min. The recovery rate in normal human serum ranges from 99.02 % to 106.34 %. This work presents a simple biosensing strategy with significant potential for application in tumor diagnosis.

Rapid enzyme-free detection of miRNA-21 in human ovarian cancerous cells using a fluorescent nanobiosensor designed based on hairpin DNA-templated silver nanoclusters

BACKGROUND

Cancer is known as one of the main non-communicable diseases and the leading cause of death in the new era. Early diagnosis of cancer requires the identification of special biomarkers. Currently, microRNAs (miRNAs) have attracted the attention of researchers as useful biomarkers for cancer early detection. Hence, various methods have been recently developed for detecting and monitoring miRNAs. Among all miRNAs, detection of miRNA-21 (miR-21) is important because it is abnormally overexpressed in most cancers. Here, a new biosensor based on silver nanoclusters (AgNCs) is introduced for detecting miR-21.

RESULTS

As a fluorescent probe, a rationally designed hairpin sequence containing a poly-cytosine motif was used to facilitate the formation of AgNCs. A guanine-rich sequence was also employed to enhance the sensing signal. It was found that in the absence of miR-21, adding a guanine-rich sequence to the detecting probe caused only a slight change in the fluorescence emission intensity of AgNCs. While in the presence of miR-21, the emission signal enhanced. A direct correlation was observed between the increase in the fluorescence of AgNCs and the concentration of miR-21. The performance of the proposed biosensor was characterized thoroughly and confirmed. The biosensor detected miR-21 in an applicable linear range from 9 pM to 1.55 nM (LOD: 2 pM).

SIGNIFICANCE

The designed biosensor was successfully applied for detecting miR-21 in human plasma samples and also in human normal and lung and ovarian cancer cells. This biosensing strategy can be used as a model for detecting other miRNAs. The designed nanobiosensor can measure miR-21 without using any enzymes, with fewer experimental steps, and at a low cost compared to the reported biosensors in this field.

Catalytic hairpin assembly-based AIEgen/graphene oxide nanocomposite for fluorescence-enhanced and high-precision spatiotemporal imaging of microRNA in living cells

The low abundance, heterogeneous expression, and temporal changes of miRNA in different cellular locations pose significant challenges for both the detection sensitivity of miRNA liquid biopsy and intracellular imaging. In this work, we report an intelligently assembled biosensor based on catalytic hairpin assembly (CHA) and aggregation-induced emission (AIE), named as catalytic hairpin aggregation-induced emission (CHAIE), for the ultrasensitive detection and intracellular imaging of miRNA-155. To achieve such goal, tetraphenylethylene-N3 (TPE-N3) is used as AIE luminogen (AIEgen), while graphene oxide is introduced to quench the fluorescence. When the target miRNA is present, CHA reaction is triggered, causing the AIEgen to self-assemble with the hairpin DNA. This will restrict the intramolecular rotation of the AIEgen and produce a strong AIE fluorescence. Interestingly, CHAIE does not require any enzyme or expensive thermal cycling equipment, and therefore provides a rapid detection. Under optimal conditions, the proposed biosensor can determine miRNA in the concentration range from 2 pM to 200 nM within 30 min, with the detection limit of 0.42 pM. The proposed CHAIE biosensor in this work offers a low background signal and high sensitivity, making it applicable for highly precise spatiotemporal imaging of target miRNA in living cells.

A New SPQC Biosensor for the Detection of a New Target of Escherichia/Shigella Genera Based on a Novel Method of Synthesizing Long-Range DNA

The rapid and sensitive detection of Escherichia/Shigella genera is crucial for human disease and health. This study introduces a novel series of piezoelectric quartz crystal (SPQC) sensors for detecting Escherichia/Shigella genera. In this innovative biosensor, we propose a new target and novel method for synthesizing long-range DNA. The method relies on the amplification of two DNA probes, referred to as H and P amplification (HPA), resulting in the products of long-range DNA named Sn. The new target was screened from the 16S rRNA gene and utilized as a biomarker. The SPQC sensor operates as follows: the Capture probe is modified on the electrodes. In the presence of a Displace probe and target, the Capture can form a complex with the Displace probe. The resulting complex hybridizes with Sn, bridging the gap between the electrodes. Finally, silver wires are deposited between the electrodes using Sn as a template. This process results in a sensitive response from the SPQC. The detection limit of the SPQC sensor is 1 CFU/mL, and the detection time is within 2 h. This sensor would be of great benefit for food safety monitoring and clinical diagnosis.

Parasite-derived microRNA let-7-5p detection for metacestodiasis based on rolling circular amplification-assisted CRISPR/Cas9

Metacestodiasis is an infectious disease caused by the larval stage of cestode parasites. This disease poses a serious health hazard to wildlife, livestock, and humans, and it incurs substantial economic losses by impacting the safety of the livestock industry, the quality of meat production, and public health security. Unfortunately, there is currently no available molecular diagnostic method capable of distinguishing cysticercus- and Echinococcus-derived microRNAs (miRNAs) from other helminthes and hosts in the plasma of metacestode-infected animals. This study aims to develop a specific, sensitive, and cost-efficient molecular diagnostic method for cysticercosis and echinococcosis, particularly for early detection. The study developed a rolling circular amplification (RCA)-assisted CRISPR/Cas9 detection method based on parasite-derived miRNA let-7-5p. Using a series of dilutions of the let-7 standard, the limit of detection (LOD) of the qPCR, RCA, and RCA-assisted CRISPR/Cas9 methods was compared. The specificity of qPCR and CRISPR/Cas9 was evaluated using four artificially synthesized let-7 standards from different species. A total of 151 plasma samples were used to evaluate the diagnostic performance. Additionally, the study also assessed the correlation between plasma levels of let-7-5p, the number of Taenia pisiformis cysticerci, and the weight of Echinococcus multilocularis cysts. The results demonstrated that the RCA-assisted CRISPR/Cas9 assay could significantly distinguish let-7 from cestodes and other species, achieving a LOD of 10 aM; the diagnostic sensitivity and specificity for rabbit cysticercosis and mouse E. multilocularis were 100% and 97.67%, and 100% and 100%, respectively. Notably, let-7-5p gradually increased in the plasma of T. pisiformis-infected rabbits from 15 days post infection (dpi), peaked at 60 dpi, and persisted until 120 dpi. In E. multilocularis-infected mice, let-7-5p gradually increased from 15 dpi and persisted until 90 dpi. Furthermore, the expression of let-7-5p positively correlated with the number of cysticerci and cyst weight. These results indicated that the let-7-5p-based RCA-assisted CRISPR/Cas9 assay is a sensitive and specific detection method that can be used as a universal diagnostic method for metacestodiasis, particularly for early diagnosis (15 dpi).

DNA-directed formation of plasmonic core-satellite nanostructures for quantification of hepatitis C viral RNA

Hepatitis C virus (HCV) continues to be a significant public health challenge, affecting an estimated 71 million people globally and posing risks of severe liver diseases. Despite advancements in treatments, diagnostic limitations hinder the global elimination efforts targeted by 2030. This study introduces an innovative diagnostic approach, integrating catalytic hairpin assembly (CHA) with plasmonic core-satellite gold nanoparticle (AuNP) assemblies, to enable sensitive and specific detection of HCV RNA. We optimized the stoichiometry of DNA hairpins to form highly stable three-way junctions (3WJs), minimizing non-specific reactions in an enzyme-free, isothermal amplification process. The resulting dual-transduction biosensor combines colorimetric and surface-enhanced Raman spectroscopy (SERS) techniques, utilizing the Raman reporter malachite green isothiocyanate (MGITC) for signal generation. Our system targets a conserved 23-nucleotide sequence within the HCV 5'-UTR, essential for RNA replication, facilitating pan-genotypic HCV detection that complements direct-acting antiviral strategies. We evaluated the biosensor's efficacy using fluorescence spectroscopy, native PAGE, AFM, and TEM. Findings indicate that the 60 nm core AuNPs surrounded by 20 nm satellite AuNPs achieved a ten-fold increase in sensitivity over the 10 nm satellites, detecting HCV RNA concentrations as low as 1.706 fM. This sensitivity is crucial, given the extremely low viral loads present during early infection stages. Our research demonstrates the promise of enzyme-free molecular biosensors for HCV, with the potential to provide cost-efficient, rapid, point-of-care testing, although further sensitivity enhancements are needed to address the challenges of early-stage detection.

Hybridization chain reaction assisted terahertz metamaterial biosensor for highly sensitive detection of microRNAs

MicroRNA (miRNA) is closely related to the occurrence and development of cancer. Accurate determination of the miRNA concentration is of great significance for early cancer diagnosis. However, due to the short sequence and low concentration of miRNA, it is still a challenge to achieve low-concentration detection. In this work, we proposed a method for the highly sensitive detection of miRNA-21 using a terahertz (THz) metamaterial sensor combined with a Hybridization chain reaction (HCR). First, a capture hairpin probe was combined with gold nanoparticles (AuNPs), which were then modified to the surface of the sensor for specific binding of miRNA-21. Then the signal amplification technique of HCR is used to amplify the trace amount of miRNA, and the super-long dendritic DNA macromolecules are formed on the surface of the sensor. This changes the dielectric environment of the sensor surface, and the resonance frequency of the sensor is shifted. The method has good specificity and sensitivity, and the concentration of miRNA-21 in the range of 100 aM to 10 nM shows excellent linear relationship with frequency shift. Most importantly, it paves the way for low-cost, easy-to-operate and marker-free miRNA detection.

A dual-mode method for detection of miRNA based on the photoluminescence and resonance light scattering

MicroRNAs (miRNAs) hold potential as useful biomarkers for early diagnosis and evaluation of diverse cancers, but their low abundance and short length make the detection of miRNAs face low sensitivity and accuracy. Herein, a photoluminescence (PL)-resonance light scattering (RLS) dual-mode method was developed for the sensitive and accurate detection of miRNA-141 using CdTe quantum dots (QDs) and Au nanoparticles. The presence of miRNA-141 induced PL quenching and RLS increasing. The limit of detection (LOD) was as low as 3.7 fM, and the miRNA-141 was detected linearly in a range from 10 fM to 10 nM. The dual signals generated no mutual interference and were detected using the same spectrophotometer, allowing for mutual validation to ensure the accuracy and reliability of the detection results. This study proposes valuable references for constructing dual-mode detection methods.

A simple, sensitive and label-free method for miRNA analysis in gastric cancer via catalytic hairpin assembly assisted programming of split-G-quadruplexes

Accurate analysis of miRNA is valuable for the diagnosis of various diseases. Herein, a sensitive and accurate fluorescence method was developed for miRNA detection based on catalytic hairpin assembly (CHA) and split-G-quadruplex (split-G4) based signal reactions. The presence of target miRNA activated the CHA process through unfolding the H1 probe, which could continuously induce the proximity of split-G4. The formed intact G4 can be specifically recognized by the commercial fluorescent dye ThT (thioflavin T), allowing for the highly sensitive, label-free detection of miRNAs. By utilizing split-G4 to generate a signal, the method exhibited a low background signal and a high reliability. In addition, the method is demonstrated to be applied for clinical sample detection, implying its promising prospect for disease diagnosis.

A graphene-oxide-based fluorometric assay for norA gene transcription in MRSA using Nb.BbvCI-assisted target recycling and T7 exonuclease-triggered cascade dual recycling signal amplification

We describe a graphene oxide (GO)-based bioassay for the fluorometric determination of norA gene transcription (mRNA) in methicillin-resistant Staphylococcus aureus (MRSA). This approach is based on Nb.BbvCI-assisted target recycling (NATR) and T7 exonuclease (T7 Exo)-triggered cascade dual-recycling signal amplification (TTCDRSA). The system included GO, a capture probe (CP), an assistant probe (AP), two carboxyfluorescein (FAM)-labeled hairpins (HP1 and HP2), endonuclease Nb.BbvcI, and exonuclease T7. In the presence of a target, AP, together with the target RNA, can hybridise with CP via partial complementarity to one another and open its hairpin structure to form a triple complex that is recognised by Nb.BbvCI. Once the CP is cleaved, the released AP and target RNA can walk on the carboxylated graphene oxide (CGO) surface to bind with another CP which induces the next round of cleavage, accumulating many trigger probes (TPs). The TPs then activate TTCDRSA with the assistance of T7 Exo, HP1, and HP2 to produce large amounts of free FAMs. These free FAMs are repelled by GO and exhibit enhanced fluorescence signals at excitation/emission wavelengths of 480/514 nm. The limit of detection (LOD) of the bioassay was calculated to be 0.37 fM, and the linear range of the method ranged from 1 fM to 1 nM. More importantly, the bioassay also exhibited high sensitivity and selectivity for target RNA detection in real samples, which may open a new promising avenue for monitoring drug efflux and studying the mechanisms of drug actions.

Recent Progress in Development and Application of DNA, Protein, Peptide, Glycan, Antibody, and Aptamer Microarrays

Microarrays are one of the trailblazing technologies of the last two decades and have displayed their importance in all the associated fields of biology. They are widely explored to screen, identify, and gain insights on the characteristics traits of biomolecules (individually or in complex solutions). A wide variety of biomolecule-based microarrays (DNA microarrays, protein microarrays, glycan microarrays, antibody microarrays, peptide microarrays, and aptamer microarrays) are either commercially available or fabricated in-house by researchers to explore diverse substrates, surface coating, immobilization techniques, and detection strategies. The aim of this review is to explore the development of biomolecule-based microarray applications since 2018 onwards. Here, we have covered a different array of printing strategies, substrate surface modification, biomolecule immobilization strategies, detection techniques, and biomolecule-based microarray applications. The period of 2018-2022 focused on using biomolecule-based microarrays for the identification of biomarkers, detection of viruses, differentiation of multiple pathogens, etc. A few potential future applications of microarrays could be for personalized medicine, vaccine candidate screening, toxin screening, pathogen identification, and posttranslational modifications.

A graphene-oxide-based aptasensor for fluorometric determination of chloramphenicol in milk and honey samples utilizing exonuclease III-assisted target recycling and Nb.BbvCI-powered DNA walker cascade amplification

Herein, a graphene oxide (GO)-based fluorescence aptasensor was developed for the sensitive and selective detection of chloramphenicol (CAP), based on exonuclease III (Exo III)-assisted target recycling and Nb.BbvCI-driven DNA walker cascade amplification. Interactions between CAP, hairpin1(HP1), hairpin2 (HP2), and 3'-amino modified hairpin3 (HP3) labeled with carboxyfluorescein (FAM) and covalently coupled to GO enabled efficient CAP detection. CAP was quantitatively assayed by measuring fluorescence at excitation/emission wavelengths of 480/514 nm, resulting from the accumulation of released FAM. A good linear range of 1 fM to 1 nM and a limit of detection (LOD) of 0.875 fM (signal-to-noise (S/N)= 3) were achieved. This aptasensor can distinguish the CAP from interference antibiotics with good specificity and selectivity, even if the concentration of the interfering substance is ten-fold higher than the target concentration. Moreover, the developed fluorescence aptasensor was successfully applied for the detection of CAP in spiked milk and honey samples. Thus, this method is potentially applicable for assaying CAP in foods and provides a promising strategy for the development of fluorescence aptasensors for environmental sample analysis.

Accurate detection of lung cancer-related microRNA through CRISPR/Cas9-assisted garland rolling circle amplification

BACKGROUND

MicroRNA (miRNA) is reported to be closely related to a variety of pathophysiological processes for carcinoma and considered a potential biomarker for the diagnosis of lung cancer with brain metastasis. However, developing an accurate and sensitive miRNA detection method has proven to be a challenge. The aim of the present study was to integrate the advantages of rolling circle amplification (RCA), clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated nucleases 9 (Cas9), and catalytic hairpin assembly (CHA) technologies to develop an miRNA detection method.

METHODS

In the present study, we developed a novel approach for the sensitive and accurate detection of miRNA through integrating garland RCA and CRISPR/Cas9-assisted signal generation. In this method, target miRNA cyclized dumbbell padlock and triggered the RCA process to form long single-stranded DNA products with a repeated hairpin structure. Double-stranded DNA sequences (dsDNA) were formed with the addition of complementary sequences. With the assistance of the Cas9 enzyme for specific recognition and cleavage of formed dsDNA, RCA products were disassembled into hairpin probes. The generated hairpin probe could be unfolded by target miRNA to initiate the CHA process for signal generation.

RESULTS

Through integration of the RCA and CHA processes, the method demonstrated favorable detection performance. The correlation equation between the signal and concentration of target miRNA was determined to be Y=312.3 × lgC + 2108, with a high correlation coefficient of 0.9786. The approach also exhibited high selectivity to the mismatched miRNAs.

CONCLUSIONS

Our method could be used in the screening, diagnosis, and prognosis of multiple diseases without complicated thermal cycling instrumentation.

Isothermal circular strand displacement-based assay for microRNA detection in liquid biopsy

Extracellular miRNAs are promising targets for developing new assays for the early diagnosis and prognosis of diseases based on liquid biopsy. The detection of miRNAs in liquid biopsies is challenged by their short sequence length, low concentration, and interferences with bodily fluid components. Isothermal circular strand displacement polymerization has emerged as a convenient method for nucleic acid amplification and detection. Herein, we describe an innovative strategy for microRNA detection directly from biological fluids based on hairpin probe-assisted isothermal amplification reaction. We designed and optimized the assay to detect target analytes in 1 µL of the complex media's biological matrix using a microfluidic device for the straightforward analysis of multiple samples. We validated the assay to detect circulating miR-127-5p in synovial fluid, recently indicated as a predictive biomarker for osteoarthritis disease. The combined use of a mutant polymerase operating with high yield and a primer incorporating locked nucleic acid nucleosides allowed detection of miR-127-5p with 34 fmol L-1 LOD. We quantified circulating miR-127-5p directly in synovial fluid, thus demonstrating that the assay may be employed for the convenient detection of 4.3 ± 0.5 pmol L-1 concentrated miRNAs in liquid biopsy samples.

Programmable, Universal DNAzyme Amplifier Supporting Pancreatic Cancer-Related miRNAs Detection

The abnormal expression of miRNA is closely related to the occurrence of pancreatic cancer. Herein, a programmable DNAzyme amplifier for the universal detection of pancreatic cancer-related miRNAs was proposed based on its programmability through the rational design of sequences. The fluorescence signal recovery of the DNAzyme amplifier showed a good linear relationship with the concentration of miR-10b in the range of 10–60 nM, with a detection limit of 893 pM. At the same time, this method displayed a high selectivity for miR-10b, with a remarkable discrimination of a single nucleotide difference. Furthermore, this method was also successfully used to detect miR-21 in the range of 10–60 nM based on the programmability of the DNA amplifier, exhibiting the universal application feasibility of this design. Overall, the proposed programmable DNAzyme cycle amplifier strategy shows promising potential for the simple, rapid, and universal detection of pancreatic cancer-related miRNAs, which is significant for improving the accuracy of pancreatic cancer diagnosis.

Determination of microRNA-122 in hepatocytes by two-step amplification of duplex-specific nuclease with laser-induced fluorescence detection

MicroRNAs (miRNAs) play important roles in physiological and pathological processes of cells. To develop a fast, simple and sensitive method to determine miRNAs is significant for miRNA studies. In this work, determination of microRNA-122 (miR-122) was achieved by laser-induced fluorescence (LIF) detection. A vial-LIF interface was first applied for sample analysis. A two-step amplification of the fluorescence signal for miR-122 was designed and realized by applying duplex-specific nuclease in the cleaving of two sensing probes. Under optimized conditions, the analysis of a miR-122 sample could be completed in less than 50 min. Only 10 μL sample was required for each test and the detection limit for the method was 0.60 pM equal to 1.2 amol of miR-122 in 10 μL solution. Lastly, the developed method was successfully applied to determine miR-122 in chicken and duck liver. The developed method was fast, selective, sensitive and sample-saving for the determination of miRNAs.

Facile, Rapid, and Low-Cost Detection for Influenza Viruses and Respiratory Syncytial Virus Based on a Catalytic DNA Assembly Circuit

Influenza viruses and respiratory syncytial virus (RSV) have contributed to severe respiratory infections, causing huge economic and healthcare burdens. To achieve rapid and precise detection of influenza viruses and RSV, we proposed a catalytic hairpin assembly (CHA) combined with the lateral flow immunoassay (CHA-LFIA) detection method. The presence of the target RNA triggers the initiation of CHA circuits. H1/H2 complexes, the amplified signal products, which were labeled with digoxin and biotin, were detected with a highly sensitive lateral flow immunoassay system. The sensitivity of the CHA-LFIA system to influenza A and B viruses and RSV reached up to 1, 1, and 5 pM, respectively. In addition, this method exhibited excellent capability for differentiating between target RNA and base-mismatched RNA. The results demonstrated that an enzyme-free, rapid, highly sensitive, and specific method had been developed to detect influenza A and B viruses and RSV.

Modern Methods for Assessment of microRNAs

The review discusses modern methods for the quantitative and semi-quantitative analysis of miRNAs, which are small non-coding RNAs affecting numerous biological processes such as development, differentiation, metabolism, and immune response. miRNAs are considered as promising biomarkers in the diagnosis of various diseases.

Aptamer-Initiated Catalytic Hairpin Assembly Fluorescence Assay for Universal, Sensitive Exosome Detection

Cancer-cell-derived exosomes are regarded as noninvasive biomarkers for early cancer diagnosis because of their critical roles in intercellular communication and molecular exchange. A robust aptamer-initiated catalytic hairpin assembly (AICHA) fluorescence assay is proposed for universal, sensitive detection of cancer-derived exosomes. The AICHA was verified with the specific detection of MCF-7 cell-derived exosomes with a wide calibration range of 8.4 particles/μL to 8.4 × 10⁵ particles/μL and a low detection limit (LOD) of 0.5 particles/μL. The universality of the AICHA method was verified for PANC-1 cell-derived exosomes, the LOD of which was determined to be 0.1 particles/μL. The performances in serum samples were detected with a recovery rate range of 95.45-106.2%, which demonstrates its significant potential for protein biomarker analysis and cancer diagnosis.

Recent advances in catalytic hairpin assembly signal amplification-based sensing strategies for microRNA detection

Accumulative evidences have indicated that abnormal expression of microRNAs (miRNAs) is closely associated with many health disorders, making them be regarded as potentialbiomarkers for early clinical diagnosis. Therefore, it is extremely necessary to develop a highly sensitive, specific and reliable approach for miRNA analysis. Catalytic hairpin assembly (CHA) signal amplification is an enzyme-free toehold-mediated strand displacement method, exhibiting significant potential in improving the sensitivity of miRNA detection strategies. In this review, we first describe the potential of miRNAs as disease biomarkers and therapeutics, and summarize the latest advances in CHA signal amplification-based sensing strategies for miRNA monitoring. We describe the characteristics and mechanism of CHA signal amplification and classify the CHA-based miRNA sensing strategies into several categories based on the "signal conversion substance", including fluorophores, enzymes, nanomaterials, and nucleotide sequences. Sensing performance, limit of detection, merits and disadvantages of these miRNA sensing strategies are discussed. Moreover, the current challenges and prospects are also presented.

A Cascaded DNA Circuit in Bead Arrays for Quantitative Single-Cell MicroRNA Analysis

Single-cell microRNA (miRNA) analysis helps people understand the causes of diseases and formulate new disease treatment strategies. However, miRNA from a single cell is usually very rare and requires signal amplification for accurate quantification. Here, to amplify the signal, we constructed the cascaded DNA circuits consisting of catalytic hairpin assembly and hybrid chain reaction into the bead array platform, on which the uniformly distributed beads were adopted for miRNA quantification. After exponential signal amplification, a consistent linear correlation between the percentage of fluorescent beads and the copy number of miRNA was detected. The proposed bead array can achieve ultrahigh sensitivity as low as 60 copies of miR-155 and high specificity for distinguishing single nucleotide differences. This method has been successfully applied to the quantitative detection of miRNA in a single cancer cell. The high sensitivity, programmability, and simple workflow of the bead array chip will give a huge advantage in basic and clinical research.