Application Of DNA Biosensors For Detecting Some Tumor Markers

The emergence of DNA biosensors have attracted the attention of researchers in many fields.It is an analytical device that integrated with the sensitive element of the detector,the transducer and the signal processor to detect analytes based on the stability of DNA itself and Watson-Crick base pair.Combined with nanomaterials,the nano biosensor has become research hotspot in the fields of early cancer screening and diagnosis in recent years due to its advantages of simplicity,quickness,accuracy,and good biological compatibility.In the construction of DNA biosensor,it is of great scientific significance to improve the performance of biosensor with some new methods and technologies for tumor markers detection,which will provide a reference value for the clinical diagnosis of cancer.The article includes two chapters:Chapter one:in this chapter,a fluorescent biosensor based on the photothermal effect of PDANs and the characters of locked nucleic acid（LNA）was provided for Alu sequence detection.The detection principle was that with the coordination of Ca²⁺,probe DNA labeled with FAM and LNA was attached on the surface of PDANs,which narrowed the distance between probe DNA and PDANs.As a result the fluorescence of FAM was quenched via the fluorescence resonance energy transfer（FRET）.In the presence of target sequence（Alu sequence）,the Probe DNA would hybridize with the Alu sequence to form double-stranded DNA（ds DNA）.At this moment,ds DNA escaped from the surface of PDANs due to the weak adsorption capacity between PDANs and ds DNA,resulting that the recovery of FAM’s fluorescence.According to the change of fluorescence signal,the target was detected.The method was proposed which took advantage of the photothermal effect of PDANs to obtain the proper temperature by laser and based on the different melting temperature of different ds DNA structure and the characteristics of LNA,the system reduced the interference from other sequences and realized Alu sequence detection specifically.The linear dynamic range was from 5 n M to 100 n M with a LOD of 1.30 n M.The sensor is expected to provide a rapid,simple,environmental detection in various biological samples.Chapter two:In this chapter,we developed an electrochemical aptasensor based on the technique of target-induced split aptamer fragments conjunction for the determination of Vascular Endothelial Growth Factor（VEGF）.The detection principle was:firstly,capture probe（CP）was attached to the modified Nano-Palladium（Nano-Pd）on the surface of Glassy Carbon Electrode（GCE）.Then,signal probe（SP）and VEGF were added to the system,which would connected the CP to form a stable complex at the electrode surface,resulting that ferrocene（Fc）groups modified in SP got close to the electrode surface,thus electrical signal would be observed.Conversely,in the absence of VEGF,the signal was not to be detected.Finally,the quantitative analysis of VEGF can be implemented by measuring the change in the electrical signal intensity.The result demonstrated that this biosensor displayed a good linear range of 5 p M～40 p M with a LOD of 0.4 p M.So,this chapter introduces an efficient,simple,and sensitive electrochemical biosensor,which is expected to be widely used in diagnosis of major clinical diseases.