UV Photodamage-Mediated Unwinding Of Double-Stranded DNA And Its Application In Biorecognition Reaction

Overexposure to UV irradiation leads to skin cancers and many other skin diseases.DNA is the main target of UV irradiation,and the analysis of UV-induced DNA damage is of great significance to the understanding of the disease evolution mechanism.At present,the effect of UV photodamage on the DNA double helix structure is still not fully understood.In this thesis,the spatial configuration change of DNA molecules before and after UV irradiation(UVC,200-280 nm)is fully studied by fluorescence and UV-vis absorption spectroscopy,providing clear evidence for DNA deformation caused by UV photodamage.On the basis of the above results,the UV photodamage-controlled toehold-mediated strand displacement reaction(TSDR)is proposed.The main contents are as follows:(1)Evidenced by fluorescence spectroscopy,fluorescence quenching is obtained for DNA dual-labeled with carboxyfluorescein and black hole quencher due to the formation of stable double-stranded structure,while UVC irradiation enhancs the fluorescence intensity by more than 200 times.Upon UVC irradiation,the fluorescence of the fluorophore intercalated into the double-stranded DNA significantly decreases,indicating that DNA undergoes obvious double-stranded unwinding and the degree of unwinding depends on the sequence composition.Based on the UV-vis absorption spectroscopy,the photodamage level of DNA increases with the number of consecutive pyrimidine bases,and the UV irradiation causes significant damage to pyrimidine-rich DNA,but exerts negligible effect on purine-rich single-stranded DNA.Similar results are also observed for uracil-rich RNA.Single-stranded DNA can be adsorbed on the surface of gold nanoparticles by ring nitrogen,exocyclic amino or keto groups in the purine or pyrimidine rings,thus protecting gold nanoparticles from salt-induced aggregation.Double-stranded DNA is unable to be adsorbed on the surface of gold nanoparticles due to the formation of ordered complementary base pairs,which leads to salt-induced aggregation of gold nanoparticles.However,UV-damaged double-stranded DNA can effectively inhibit the aggregation of gold nanoparticles,suggesting that UV photodamage can induce the unwinding of double-stranded DNA.(2)DNA can be folded into nanostructures of various shapes and functions through DNA hybridization between complementary base pairs.To achieve specific response of functional DNA to certain stimuli,the design of controllable biorecognition reaction is of great importance.As an effective biorecognization means,TSDR has been widely used in biological analysis.As the UV-mediated photodamage of DNA is dependent on pyrimidine bases,proper insertion of pyrimidine bases enables the unwinding of DNA at specific sites.Therefore,complementary DNA strand is used to block the toehold to form double-stranded DNA in this paper,and then the double-stranded DNA is unwound by UV photodamage to expose toehold,and finally the target DNA triggers TSDR.UV photodamage-controlled TSDR for target assay is proposed on the basis of above results,providing a simple and reliable alternative for the design of photocontrolled biorecognition reaction.