Application Of DNA Nanomachines In Biological Detection And The Impact Of G-quadruplex Toehold Structure On DNA Strand Exchange

With the development of DNA nanotechnology, more and more DNA namomachines have been created and applied in biological detection, therapy diagnosis, medication and computation. Modern biosensors require high sensitivity, great signal enhancement and extensive applicability for detection and diagnostic purposes. Traditional molecular beacons do not meet these requirements because of the lack of signal amplification. The current amplification pathways using enzymes, DNAzymes and nanoparticles are usually quite sophisticated and are limited to specific applications. Herein, we developed simple biosensors based on the structure of kissing-hairpin. Through hybridization amplification of these nanomachines, the evolved MBs could greatly enhance the detected signals, reduce the sensing limits for targets and, remarkably, distinguish single-base mismatches specifically for nucleic acid detection. In addition, these new MBs can be directly applied in living cells. By introducing aptamer sequences, these novel sensors can also detect proteins and small molecules. These properties were exemplified by the detection of both the ?-actin gene and thrombin. The simplicity, sensitivity and flexibility of these devices make them appropriate for more expansive applications.DNA nanotechnology has been studied for a long time, and utilized in various applications. Toehold-mediated strand displacement plays an essential role. In most conditions, the toehold hybridization relies on Watson-Crick base pairing. Tetraplexes-based toehold has been proposed, but it still needs intensive researches. In this work, a new type of strand displacement is designed based on the G-quadruplex-mediated toehold. This strategy can be regulated by adjusting the concentration and polymerization degrees of PEG and by changing the number of G-quartets or the split mode of G-quadruplex. This displacement could also be achieved with the help of a mutation in migration strand in aqueous solution. And we first apply this strategy in the hybridization chain reaction. Large amount of G-quadruplexes are continuously assembled during the amplification triggered by target DNA. With the characteristics of low cost, label-free, sensitivity and selectivity, the method has the potential in DNA nanomachines, biosensing and disease diagnosis.