Triple cascade reactions: An ultrasensitive and specific single tube strategy enabling isothermal analysis of microRNA at sub-attomole level

G-wire-based self-quenched fluorescence probe combining with target-activated isothermal cascade amplification for ultrasensitive microRNA detection

Herein, we reported the G-wire-based self-quenched fluorescence probe and its application in ultrasensitive microRNA (miRNA) detection by combining with target-activated isothermal cascade amplification. The terminal-single-fluorescein (FAM)-labeled G-rich oligonucletides self-assembled into G-wire nanostructures (G-wires) with K⁺ and Mg²⁺. Thereafter, the G-wires brought terminal-labeled FAM into close proximity, as a result, the self-quenched signal probe formed. Besides, when there was the target miRNA, target-activated isothermal cascade amplification converted miRNA into the copious trigger DNA. After hybridization between trigger DNA and the self-quenched probe, the G-wires were splited and forced the apart of proximate FAM, and then the self-quenched probe displayed an "on" mechanism. Therefore, the approach gave a limit of detection (LOM) of 0.82 aM to miRNA-21 and could be implemented within a wide linear range of 2 aM to 2 nM. This approach was able to distinguish the single-mismatched miRNA-21, which was selective and sensitive in detecting human spiked serum samples.

Label-free detection of microRNA: two-stage signal enhancement with hairpin assisted cascade isothermal amplification and light-up DNA-silver nanoclusters

A method is described for the determination of microRNAs via two-stage signal enhancement. This is attained by combining hairpin (HP) assisted cascade isothermal amplification with light-up DNA-Ag nanoclusters. A rationally designed dual-functional HP is used, and microRNA-21 is chosen as a model analyte. At the first stage, upon the hybridization of the microRNA-21 with HP, microRNA recycling via polymerase-displacement reaction and a circulative nicking-replication process are achieved. This generates numerous G-abundant overhang DNA sequences. In the second stage, the above-released G-abundant overhang DNA sequences hybridize with the dark green Ag NCs, and this results in the appearance of bright red fluorescence. Thanks to the two signal enhancement processes, a linear dependence between the fluorescence intensity at 616 nm and the concentration of microRNA-21 is obtained in the range from 1 pM to 20 pM with a detection limit of 0.7 pM. The strategy clearly discriminates between perfectly-matched and mismatched targets. The method was applied to the determination of microRNA-21 in a spiked serum sample. Graphical abstractSchematic representation of microRNA detection by integrating hairpin assisted cascade isothermal amplification with light-up DNA Ag nanoclusters. With microRNA, G-abundant overhang DNA sequences from amplification reaction hybridize with dark green Ag nanoclusters to produce a concentration-dependent bright red fluorescence.

g-C3N4 nanosheet-based ratiometric fluorescent probes for the amplification and imaging of miRNA in living cells

By using BCNNS as a nanocarrier, a fluorescence quencher and an interior label, and using CuNC-labeled hairpin DNA for dual-signal output, a dual-emission ratiometric fluorescent probe was fabricated for the measurement of intracellular miRNA.

Combining Affinity Selection and Specific Ion Mobility for Microchip Protein Sensing

The sensitive detection of proteins is a key objective in many areas of biomolecular science, ranging from biophysics to diagnostics. However, sensing in complex biological fluids is hindered by nonspecific interactions with off-target species. Here, we describe and demonstrate an assay that utilizes both the chemical and physical properties of the target species to achieve high selectivity in a manner not possible by chemical complementarity alone, in complex media. We achieve this objective through a combinatorial strategy, by simultaneously exploiting free-flow electrophoresis for target selection, on the basis of electrophoretic mobility, and conventional affinity-based selection. In addition, we demonstrate amplification of the resultant signal by a catalytic DNA nanocircuit. This approach brings together the inherent solution-phase advantages of microfluidic sample handling with isothermal, enzyme-free signal amplification. With this method, no surface immobilization or washing steps are required, and our assay is well suited to monoepitopic targets, presenting advantages over conventional ELISA techniques.

Specific and relative detection of urinary microRNA signatures in bladder cancer for point-of-care diagnostics

We present a dual-isothermal cascade strategy assisted by a lateral flow peptide nucleic acid biosensor for point-of-care detection of urinary microRNAs without a temperature protocol and complex instruments. The proposed assay is expected to be of great promise for bladder cancer diagnosis and point-of-care diagnostics.

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.

Label-free, homogeneous, and ultrasensitive detection of pathogenic bacteria based on target-triggered isothermally exponential amplification

A novel colorimetric biosensing strategy for highly selective and ultrasensitive detection of pathogenic bacteria based on target-triggered EXPAR by the property of polymerase and nicking activity of restriction endonuclease has been reported.