Sensitive and specific detection of miRNA using an isothermal exponential amplification method using fluorescence-labeled LNA/DNA chimera primers

Rapid detection of EGFR mutation in CTCs based on a double spiral microfluidic chip and the real-time RPA method

Circulating tumor cells (CTCs) are cells shed from primary or metastatic tumors and spread into the peripheral bloodstream. Mutation detection in CTCs can reveal vital genetic information about the tumors and can be used for "liquid biopsy" to indicate cancer treatment and targeted medication. However, current methods to measure the mutations in CTCs are based on PCR or DNA sequencing which are cumbersome and time-consuming and require sophisticated equipment. These largely limited their applications especially in areas with poor healthcare infrastructure. Here we report a simple, convenient, and rapid method for mutation detection in CTCs, including an example of a deletion at exon 19 (Del19) of the epidermal growth factor receptor (EGFR). CTCs in the peripheral blood of NSCLC patients were first sorted by a double spiral microfluidic chip with high sorting efficiency and purity. The sorted cells were then lysed by proteinase K, and the E19del mutation was detected via real-time recombinase polymerase amplification (RPA). Combining the advantages of microfluidic sorting and real-time RPA, an accurate mutation determination was realized within 2 h without professional operation or complex data interpretation. The method detected as few as 3 cells and 1% target variants under a strongly interfering background, thus, indicating its great potential in the non-invasive diagnosis of E19del mutation for NSCLC patients. The method can be further extended by redesigning the primers and probes to detect other deletion mutations, insertion mutations, and fusion genes. It is expected to be a universal molecular diagnostic tool for real-time assessment of relevant mutations and precise adjustments in the care of oncology patients.

Isothermal exponential amplification reactions triggered by circular templates (cEXPAR) targeting miRNA

BACKGROUND

Isothermal exponential amplification reaction (EXPAR) is an emerging amplification technique that is most frequently used to amplify microRNA (miRNA). However, EXPAR also exhibits non-specific background amplification in the absence of the targeted sequence, which limits the attainable assay sensitivity of EXPAR.

METHODS AND RESULTS

A novel modified isothermal EXPAR based on circular amplification templates (cEXPAR) was developed in this study. The circular template consists of two same linear fragments that complement the target sequence, and these two linear fragments are separated by two nicking agent recognition sequences (NARS). Compared with the linear structure template, this circular template allows DNA or RNA fragments to be randomly paired with two repeated sequences and can be successfully amplified. This reaction system developed in this study could rapidly synthesize short oligonucleotide fragments (12-22 bp) through simultaneous nicking and displacement reactions. Highly sensitive chain reactions can be specifically triggered by as low as a single copy of target molecule, and non-specific amplification can be effectively eliminated in this optimized system. Moreover, the proposed approach applied to miRNA test can discriminate single-nucleotide variations between miRNAs.

CONCLUSION

The newly developed cEXPAR assay provides a useful alternative tool for rapid, sensitive, and highly specific detection of miRNAs.

Updated review of advances in microRNAs and complex diseases: experimental results, databases, webservers and data fusion

MicroRNAs (miRNAs) are gene regulators involved in the pathogenesis of complex diseases such as cancers, and thus serve as potential diagnostic markers and therapeutic targets. The prerequisite for designing effective miRNA therapies is accurate discovery of miRNA-disease associations (MDAs), which has attracted substantial research interests during the last 15 years, as reflected by more than 55 000 related entries available on PubMed. Abundant experimental data gathered from the wealth of literature could effectively support the development of computational models for predicting novel associations. In 2017, Chen et al. published the first-ever comprehensive review on MDA prediction, presenting various relevant databases, 20 representative computational models, and suggestions for building more powerful ones. In the current review, as the continuation of the previous study, we revisit miRNA biogenesis, detection techniques and functions; summarize recent experimental findings related to common miRNA-associated diseases; introduce recent updates of miRNA-relevant databases and novel database releases since 2017, present mainstream webservers and new webserver releases since 2017 and finally elaborate on how fusion of diverse data sources has contributed to accurate MDA prediction.

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.

Rolling Circle and Loop Mediated Isothermal Amplification Strategy for Ultrasensitive miRNA Detection

Rolling circle amplification (RCA) and loop mediated isothermal amplification (LAMP) were combined to establish the rolling circle and loop mediated isothermal amplification (RC-LAMP) method for miRNA detection. With the participation of Bst 2.0 DNA Polymerase, the method enabled RCA and LAMP amplification to occur simultaneously without thermal cycling. The limit of detection of RC-LAMP was 500 amol/L, which is comparable to previously reported amplification strategies. Moreover, its upper limit of quantitation was higher and showed a stronger resistance to matrix interference. Therefore, it is possible to detect low concentrations of miRNA in samples by increasing the total RNA added. Owing to its facile detection mode and simple operation, this method has great potential in clinical sample detection.

A lateral flow biosensor based on gold nanoparticles detects four hemorrhagic fever viruses

The pathogen of viral hemorrhagic fever (VHF), which is harmful to human health, is a hemorrhagic fever virus. Clinicians have long needed convenient and sensitive point-of-care rapid diagnostic tests (RDTs) for hemorrhagic fever viruses. Commonly used methods for pathogen detection rely on conventional culture-based tests, antibody-based assays and polymerase chain reaction (PCR)-based techniques. However, these methods are costly, laborious and time-consuming. Herein, we present a simple and sensitive biosensor for the rapid detection of hemorrhagic fever viruses. For this assay, we develop lateral flow biosensors (LFBs) based on magnetic beads and nicking enzyme-assisted isothermal strand-displacement amplification (SDA) for the detection of hemorrhagic fever viruses. The detection limit of this assay is 10 fM.

Beacon-mediated exponential amplification reaction (BEAR) using a single enzyme and primer

Beacon-mediated Exponential Amplification Reaction (BEAR) enables isothermal, exponential signal amplification. BEAR uses only a single enzyme and a single primer. Detection of 0.2 amol of a mitochondrial DNA with a point mutation in less than an hour demonstrates an application of the BEAR technique for nucleic acid research.

Research advances in the detection of miRNA

MicroRNAs (miRNAs) are a family of endogenous, small (approximately 22 nucleotides in length), noncoding, functional RNAs. With the development of molecular biology, the research of miRNA biological function has attracted significant interest, as abnormal miRNA expression is identified to contribute to serious human diseases such as cancers. Traditional methods for miRNA detection do not meet current demands. In particular, nanomaterial-based methods, nucleic acid amplification-based methods such as rolling circle amplification (RCA), loop-mediated isothermal amplification (LAMP), strand-displacement amplification (SDA) and some enzyme-free amplifications have been employed widely for the highly sensitive detection of miRNA. MiRNA functional research and clinical diagnostics have been accelerated by these new techniques. Herein, we summarize and discuss the recent progress in the development of miRNA detection methods and new applications. This review will provide guidelines for the development of follow-up miRNA detection methods with high sensitivity and specificity, and applicability to disease diagnosis and therapy.

Hi-fidelity discrimination of isomiRs using G-quadruplex gatekeepers

Core microRNA (miRNA) sequences exist as populations of variants called isomiRs made up of different lengths and nucleotide compositions. In particular, the short sequences of miRNA make single-base isomiR mismatches very difficult to be discriminated. Non-specific hybridizations often arise when DNA probe-miRNA target hybridization is the primary, or initial, mode of detection. These errors then become exacerbated through subsequent amplification steps. Here, we present the design of DNA probes modified with poly-guanine (PG) tracts that were induced to form G-quadruplexes (G4) for hi-fidelity discrimination of miRNA core target sequence from single-base mismatched isomiRs. We demonstrate that, when compared to unmodified probes, this G4 'gate-keeping' function within the G4-modified probes enables more stringent hybridization of complementary core miRNA target transcripts while limiting non-specific hybridizations. This increased discriminatory power of the G4-modified probes over unmodified probes is maintained even after further reverse transcriptase extension of probe-target hybrids. Enzymatic extension also enhanced the clarity and sensitivity of readouts and allows different isomiRs to be distinguished from one another via the relative positions of the mismatches.

Sensitive detection of microRNAs by duplex specific nuclease-assisted target recycling and pyrene excimer switching

Herein, we develop a sensitive fluorescence method for microRNA assay based on duplex specific nuclease-assisted target recycling and pyrene excimer switching.