Target-induced Trivalent G-quadruplex/hemin DNAzyme for Colorimetric Detection of Hg^(2+) Based on an Exonuclease III Assisted Catalytic Hairpin Assembly

Mercury ion(Hg^(2+)),a highly noxious of heavy metalion,has detrimental effects on the ecological environment and human health.Herein,we have developed an exonuclease III(Exo III)assisted catalytic hairpin assembly formation of a trivalent G-quadruplex/hemin DNAzyme for colorimetric detection of Hg^(2+).A hairpin DNA(Hr)was designed with thymine-Hg^(2+)-thymine pairs that catalyzed by Exo III is prompted to happen upon binding Hg^(2+).A released DNA fragment triggers the catalytic assembly of other three hairpins(H1,H2,and H3)to form many trivalent G-quadruplex/hemin DNA enzymes for signal output.The developed sensor shows a dynamic range from 2 pM to 2μM,with an impressively low detection limit of 0.32 pM for Hg^(2+)detection.Such a sensor also has good selectivity toward Hg^(2+)detection in the presence of other common metal ions.This strategy shows the great potential for visual detection with portable type.

Direct detection of C9orf72 hexanucleotide repeat expansions by nanopore biosensor

Diagnostic C9orf72 hexanucleotide repeat expansions(C9-HRE)is essential for the early and accurate diagnosis of amyotrophic lateral sclerosis(ALS)and will provide support for the prognosis and gene therapy of ALS.In the present study,by combining catalytic hairpin assembly(CHA)with Mycobacterium smegmatis porin A(MspA)nanopore,a new nanopore-based strategy for the detection of C9-HRE was reported.Less than 30 repeats of C9-HRE could be detected via this method,and the results have the potential to help distinguish between patients and healthy individuals.Moreover,the method demonstrated its great specificity for C9-HRE by identifying other repeat expansions.Given the high selectivity,this approach had been successfully used to detect C9-HRE in cell and blood samples with high accuracy.This detection strategy is user-friendly and has a strong anti-interference ability,thus providing a powerful tool for clinical diagnosis.

Catalytic DNA Origami-based Chiral Plasmonic Biosensor

Plasmonic circular dichroism(CD) has been emerged as a promising signal for building biosensors due to its high sensitivity and specificity. In the past years, DNA nanotechnology enabled diverse chiral plasmonic devices, which can response biomolecules and then generate dynamic plasmonic CD signals at the visible range. Although some of them have been successfully employed as biosensors, the detection sensitivity is still relatively low. Herein we report a chiral plasmonic sensor with an improved detection sensitivity by integrating catalytic hairpin assembly circuits into DNA origami structures. We tested two kinds of tumor marker RNA sequences as detection targets and it turns out that the detection limit is below 10 pmol/L, improving one order of magnitude compared to previous work. The chiral plasmonic sensor with internal signal amplification circuits can stimulate a variety of smart nano-sensors for biological detection and offer a promising strategy for pathogenic RNA detection with plasmonic CD output.

Functional nucleic acid circuitry as a universal detector for pathogens

While the pathogen nucleic acid diagnostic technology has made tremendous progresses,several challenges,including long development cycles and limited specificity still exist,especially in the context of isothermal amplification techniques.To enhance the detection accuracy,here a functional strand displacement catalytic hairpin assembly circuit,which can perform at high-temperature(HT-CHA),was developed as the downstream of the loop mediated isothermal nucleic acid amplification(LAMP).The addition of HT-CHA not only ensures the specificity but also amplifies the detection signal.Taking African swine fever(ASF)gene as the target,the input of HT-CHA was designed according to the ASF gene LAMP amplicons.This LAMP-HTCHA can detect as low as 2 copies/μL targeting genes with high signal-to-noise ratio.Through importing a three-way junction(3WJ)transducer,the HT-CHA well-developed for ASF gene can be directly adapted to detect the LAMP amplicons of other pathogen genes,such as Mycoplasma pneumoniae(MP)gene.The time-consuming and high-risk process to redesign HT-CHA components can be further avoided,making the method even general and useful for a plenty of other targets.Finally,the accurate detection of MP gene in alveolar lavage fluid samples confirmed the high potential of the LAMP and HT-CHA combination in clinical applications,providing a promising strategy to develop point-of-care diagnostics at constant temperatures.