Visual Detection Of DNA And Uranyl Ion Based On DsDNA-SYBR Green ? Photocatalytic Oxidation

SYBR Green ??SG?,a nucleic acid dye,can significantly enchance its fluorescence after bingding into double strand DNA?ds DNA?.Hence,it was widely used for for construction of flouresent biosensor.In comparision of fluorescent detection,visual detection can achieve the semi-quantification via naked eyes,thus accompanying the advantages of simplicity,free of complicated instruments,potentiality of in-field analysis etc.This dissertation is aiming at construction of a new SG-ds DNA photocatalytic system,and further using the system for low background,sensitive and label-free detection of DNA and UO₂²⁺.?I?A visual system based on ds DNA-SG photocatalytic oxidation was constructed and further applied for ultrasensitive detection of DNA.During the experiment,we found that the SG molecules after binding into ds DNA can catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine?TMB?under light irradiation corresponding to the excitation of the ds DNA-SG complex.The mechanism study illustrated that the photooxidation was grately dependent on singlet oxygen.The effect of the important parameters such as solution p H,types of ds DNA,length of ds DNA,SG concentration,incubation time of SG and ds DNA,coloration reagent,etc.,were investigated.Under the optimal conditions,the visual system can detect DNA as low as 0.05 n M.Furtherly using spectrophotometry,the system exhibited a good linear ship in the DNA concentratoion range of 0.05-1000 n M,and the limit of detection was down to 0.024 n M.Comparing with the reported G-quaduraplex DNAzyme catalysed coloration,the most appealing feature of the photocatalytic system here is that it can be obtained using random DNA sequences that can form a duplex.During its application in DNA detection,the system provided the advantes of simplicity,low background and high sensivitity,and also has promising protentiality for the determination of proteins,small molecules and metal ions.?2?A DNAzyme-modulated photosensitization system was developed for controlling the ds DNA-SYBR Green ? photooxidation of TMB.When applying the system for UO₂²⁺detection,the DNAzyme was activated by UO₂²⁺and cleaved the substrate,leading to dissociation of the complex of the enzyme strand and substrate strand.As a result,the photosensitization ability was remarkably decreased,and a much less colored solution was observed.In the experiment,the enzyme strand structure,reference dyes,DNAzyme concentration,p H,ethanol ratio,incubation time and LED illumination time were investigated.Under the optimal conditions,it can detection as low0.5 ng m L^-1 of UO₂²⁺by naked eys;using spectrophotometry,the linear range was 0.5 ng m L^-1500 ng m L^-1.The interference study showed that the common co-existing metal ions in the seawater caused a neglectable influence for detection of UO₂²⁺.The system has been successfully applied for detection of UO₂²⁺in sea water samples with recoveries ranging from 93-104%.The sensing system exhibiting the merits of simplicity,superior specifiticy and high anti-salt ability is expected to be an appealing method for semi-quantification of UO₂²⁺in sea water samples.