Nucleic Acid-dye Photocatalytic System For Visual Sensing

Aptamers has been increasingly used in biology,medicine,agriculture and other research areas due to their high specificity,high affinity,relative ease of synthesis as well as modification,and wide application.Existing nucleic acid sensors were mainly optical sensor,electrochemical sensor,and piezoelectric sensor.Owing to free of shophiscated instrument,visual detection technique has gained widespread application in sensing.In this work,a novel nucleic acid-dye based photocatalytic system was developed for visual sensing of metal ions,proteins,DNA and small molecules.The experiments of this work include three parts as follows:?1?First,a novel,simple and visual nucleic acid-dye photocatalytic system was developed for visual assay.Experiments showed that mixing fluorescent dyes with T-Hg²⁺-T mismatch,dsDNA,G-quadruplex,hairpin conformations could catalyze TMB and produce visual signals under the irradiation of LED.Then the mechanism of generating the visual phenomenon was researched.Upon intercalation of fluorescent dyes into the grooves of specific DNA structure and illuminated with LED that was corresponding to the excitation wavelength,the dye-DNA complex could be excieted,and then produce active singlet oxygen by energy transfer from the dyes to dissolved oxygen.The singlet oxygen oxidized TMB and yieded color change.In addition,five different dyes,namely ethidium bromide?EB?,methyl blue?MB?,crystal violet?CV?,Ru?phen?₃²⁺and Ru?bpy?₂?dppz?²⁺,were selected for investigation of the effect of fluorescent dyes.The results showed that all the five dye-dsDNA complex exhibited photooxidase activity.The examination of different colorants indicated that TMB,ABTS,OPD and DAB could be catalytically oxidized.But the color differences of ABTS,OPD and DAB were smaller than that of TMB.Therefore,established visual nucleic acid-based photooxidase system had a series of advantages,such as simplicity,convenience.?2?Second,the photooxidase system was used to detect Hg²⁺in aqueous solution.In the experiments,the effects of related parameters were investigated including EB concentration,solution pH,aptamer concentration and irradiation time.Under the optimum conditions,the minimal detectable concentration of Hg²⁺was 0.25 nmol/L.The presence of other metal ions?1000 nmol/L?didn't interfere the detection of 10nmol/L Hg²⁺.This approach is simple,intuitive and rapid,which can be used to monitoring Hg²⁺in real water within 30 min.Therefore,this method was expected to be applied to field testing.?3?Third,the photooxidase system was also used to detect proteins,DNA and small molecules in aqueous solution.The sensing technique can detect as low as 5 pmol/L thrombin,0.5 nmol/L DNA,and 10?mol/L cocaine by naked-eye.The method could be also used for the sensitive detection of proteins,DNA and small molecules with altering the nucleic acid sequence.