A fluorescent sensor based on strand displacement amplification and primer exchange reaction coupling for label-free detection of miRNA

Sensitive and reliable gastric ulcer related MicroRNA detection by bridge catalytic hairpin assembly (bCHA) mediated primer exchange reaction

MicroRNAs (miRNA) have a significant role in the progression of gastric ulcer, and the sensitive and reliable detection of miRNAs is pivotal for the early diagnosis and treatment of gastrointestinal diseases. In this study, we developed a novel and efficient method for detecting miRNA-122, a crucial biomarker used to assess the prognosis of gastric ulcers. This method combines the bridge catalytic hairpin assembly (bCHA)-based target sequence recycling with the primer exchange reaction (PER), resulting in a highly sensitive and label-free approach. Specifically, the bridge CHA technique, which offers superior target recognition accuracy and increased signal amplification efficiency compared to the classic CHA procedure, can selectively identify the target miRNA and release the complementary sequence to serve as a primer to facilitate the PER. This PER process produces a large number of G-quadruplex sequences, which then bind with thioflavin T to significantly increase its fluorescence. This enhanced fluorescence is used to detect miRNA-122, with a detection limit as low as 3.12 fM. The proposed approach can achieve exact discrimination of the target miRNA-122. Due to its label-free character, high selectivity, and sensitivity, this technology can serve as a practical and universal approach for detecting different biomarkers in the early stages of gastrointestinal diseases.

Nicking endonuclease-mediated primer exchange reaction for rapid and sensitive miRNA detection

Primer exchange reaction (PER) is a novel and simple nucleic acid-templated extension technique that has recently attracted much attention in the field of biosensing. However, current PER reactions have shown relatively slow rates and low amplification performances, resulting in long assay times and limited detection sensitivities. Here we report a nicking endonuclease-mediated PER reaction (named NEPER) that rapidly releases amplified DNA products by adding a nicking endonuclease to hydrolyze the hybridized double-stranded DNA (dsDNA), and consequently has a maximum speed that is thirty orders of magnitude greater than the maximum for conventional PER. We further combined a CRISPR/Cas12a signal readout technique and developed a cascade NEPER-CRISPR/Cas12a method that can detect miRNA-155 with a limit of detection (LOD) down to 3.1 fM. We also show that the NEPER-CRISPR/Cas12a can be used to detect targets in serum samples.

A Versatile Colorimetric Diagnostic Platform Based on Primer Exchange Reaction Cascades Driven Loop-Mediated Isothermal Amplification

The primer exchange reaction (PER), as a well-established and sophisticated isothermal nucleic acid amplification strategy, has been extensively employed to amplify various genetic biomarkers. However, the amplification efficiency of conventional PER is generally unsatisfactory due to its linear signal-amplifying mechanism. In this study, we developed a versatile colorimetric platform by rationally integrating Primer exchange reaction with efficient Loop-mediated isothermal amplification (LAMP), termed vcPeLa, for the rapid and sensitive detection of cancer-related biomarkers, such as microRNAs (miRNAs) and carcinoembryonic antigen (CEA). The PER cascade in the vcPeLa can be directly initiated by the target, resulting in the production of long single-stranded DNA products with repeated functional sections. These repeats in the product can serve as the template to produce a significant number of double stem-loop DNAs with the cooperation of DNA polymerase and hairpin structure primer probes. These DNAs are the primary starting materials for subsequent LAMP. A substantial quantity of pyrophosphate can be recognized by Cu2+-chelated pp Probe (pyrophosphate sensing probe). The Cu2+ is removed from the Cu2+-chelated pp Probe as a result of the formation of a complex between Cu2+ and pyrophosphate, which results in color changes. Consequently, the vcPeLa platform is feasible to detect 0.31 fM miRNA and 0.043 ng/mL CEA with high selectivity and stability without the requirement of introducing any additional reaction steps or sample transfer operations in comparison to conventional assays. Therefore, this facile and ultrasensitive vcPeLa platform provides a new promising tool for cancer diagnosis and biomarker screening.

An enzyme-free and label-free multiplex detection of miRNAs by entropy-driven circuit coupled with capillary electrophoresis

MicroRNAs (miRNAs) are currently recognized as important biomarkers for the early diagnosis and prognostic treatment of cancer. Herein, we developed a simple and label-free method for the multiplex detection of miRNAs, based on entropy-driven circuit (EDC) amplification and non-gel sieving capillary electrophoresis-LED induced fluorescence detection (NGCE-LEDIF) platform. In this system, three different lengths of fuel chains were designed to catalyze three EDC, targeting miRNA-21, miRNA-155, and miRNA-10b, respectively. In the presence of target miRNA, the EDC cycle amplification reaction was triggered, generating numerous stable double-strands products (F-DNA/L-DNA). Since the three miRNAs correspond to three different lengths of F-DNA/L-DNA, they can be easily isolated and detected by NGCE. This strategy has good sensitivity, with detection limits of 68 amol, 292.2 amol, and 394 amol for miRNA-21, miRNA-155, and miRNA-10b, respectively. Additionally, this method has good specificity and can effectively distinguish single-base mismatches of miRNA. The recoveries of the three miRNAs in deproteinized healthy human serum ranged from 91.28 % to 108.4 %, with a relative standard deviation (RSD) of less than 7.9 %. This method was further applied to detect cellular miRNAs in human breast cancer (MCF-7) cell extracts, revealing an up-regulation of miRNA-21, miRNA-155, and miRNA-10b in MCF-7 cells. The successful spiked recovery in human serum and RNA extraction from MCF-7 cells underscores the practicality of this method. Therefore, this strategy has broad application prospects in biomedical research.

Design and analysis of self-priming extension DNA hairpin probe for miRNA detection based on a unified dynamic programming framework

MicroRNAs (miRNAs) are potential biomarkers for cancer diagnosis and prognosis, methods for detecting miRNAs with high sensitivity, selectivity, and stability are urgently needed. Various nucleic acid probes that have traditionally been for this purpose suffer several drawbacks, including inefficient signal-to-noise ratios and intensities, high cost, and time-consuming method establishment. Computing tools used for investigating the thermodynamics of DNA hybridization reactions can accurately predict the secondary structure of DNA and the interactions between DNA molecules. Herein, NUPACK was used to design a series of nucleic acid probes and develop a phosphorothioated-terminal hairpin formation and self-priming extension (PS-THSP) signal amplification strategy, which enabled the ultrasensitive detection of miR-200a in serum samples. The free and binding energies of the DNA detection probes calculated using NUPACK, as well as the biological experimental results, were considered synthetically to select the best sequence and experimental conditions. A unified dynamic programming framework, NUPACK analysis and the experimental data, were complementary and improved the designed model in all respects. Our study demonstrates the feasibility of using computer technology such as NUPACK to simplify the experimental process and provide intuitive results.

SERS microfluidic chip integrated with double amplified signal off-on strategy for detection of microRNA in NSCLC

In this work, based on Fe3O4@AuNPs and double amplified signal Off-On strategy, a simple and sensitive SERS microfluidic chip was constructed to detect microRNA associated with non-small cell lung cancer (NSCLC). Fe3O4@AuNPs have two advantages of SERS enhanced and magnetic adsorption, the introduction of microfluidic chip can realize double amplification of SERS signal. First, the binding of complementary ssDNA and hpDNA moved the Raman signaling molecule away from Fe3O4@AuNPs, at which point the signal was turned off. Second, in the presence of the target microRNA, they were captured by complementary ssDNA and bound to them. HpDNA restored the hairpin conformation, the Raman signaling molecule moved closer to Fe3O4@AuNPs. At this time, the signal was turned on and strong Raman signal was generated. And last, through the magnetic component of SERS microfluidic chip, Fe3O4@AuNPs could be enriched to realize the secondary enhancement of SERS signal. In this way, the proposed SERS microfluidic chip can detect microRNA with high sensitivity and specificity. The corresponding detection of limit (LOD) for miR-21 versus miR-125b was 6.38 aM and 7.94 aM, respectively. This SERS microfluidic chip was promising in the field of early detection of NSCLC.