Design Of Functional Nucleic Acid Sensor With Multi-level Signal Amplification And Highly Sensitive Detection Of Tumor Markers And Lead Ion

With the continuous development of social productivity,people's material living standards have gradually improved,and people pay more attention to their health.Cancer is a major threat to human health,and recent studies have also shown that the incidence of cancer is increasing.In the continuous development of life science technology,people began to study the physiology and pathology of cancer at the molecular level,and found that the abnormal expression of some genes is closely related to the onset of cancer.Therefore,they are used as biomarkers of certain cancers.Secondly,another unavoidable problem in the process of social industrialization is environmental pollution.Among them,heavy metal ions will not only pollute soil and water sources,but also accumulate in the human body through the food chain,thereby causing disease or even death to the organism.In order to achieve highly sensitive detection of tumor markers and certain cancer-inducing substances,we successfully designed three biosensors based on nucleic acid probes to detect Pax-5 gene,heavy metal ions and micro RNAs(mi RNAs),respectively.The successful construction of the sensor shows that biosensors based on nucleic acid probes can be widely used in the detection of various types of substances.Firstly,a colorimetric label-free sensing system based on target triggered split-to-intact remodeling of G-rich functionalized hairpin probe has been developed for amplified signaling of Pax-5 gene.In this system,the structure of the hairpin probe is remodeled by adding the target gene,and the remodeled hairpin probe can perform isothermal amplification and forms multiple channels capable of producing G-quadruplexes.When specifically combined with hemin,the formed G-quadruplex-hemin complexes,also known as DNAzymes,can strongly catalyze the oxidization of TMB to a colored TMB⁺,realizing the colorimetric detection of the Pax-5 gene,and the limit of detection is 3.2 p M.In addition,the biosensor also exhibits good detection performance in complex biological environments.Secondly,we propose a cascade signal amplification sensor based on DNAzyme-based strand displacement reaction(SDR)and hybridization chain reaction(HCR)for high-sensitivity detection of Pb²⁺.In the sensor system,the target metal ion can activates DNAzyme to cause SDR,and then under the synergistic action of polymerase and nickase,a large amount of DNA strands that can initiate HCR are generated and finally a strong fluorescent signal is generated to achieve detection of Pb²⁺,and the limit of detection is 16.8 p M.And we have also proved that the sensor can still maintain excellent detection performance in complex environments such as lake water,milk and human serum.Finally,a new fluorescence strategy was proposed for the enzyme-free sensing of let-7a by combining the SDR with the HCR.The sensor was successfully applied to the detection of the let-7a gene with a wide linear range from 25 p M to 250 n M and a limit of detection of 9.01 p M.In addition,the sensor has a good ability to discriminate non-target genes,and it can also detect target genes with high sensitivity in complex human serum samples.