Detection Of Biomolecules And Hg²⁺ Ions Based On The Fluorescent Silver Nanoclusters Templated By The DNA

In the past few years,DNA-templated silver nanoclusters?DNA-Ag NCs?have attracted many researchers because of their ultrasmall size and excellent optical properties.In this study,some different sequences of DNA have been designed as templates to synthesize the DNA-Ag NCs,and then the optical properties of these DNA-Ag NCs have been researched,respectively.Finally the DNA-Ag NCs which possess good fluorescent property was selected to study on the detection of biomolecules and Hg²⁺ ions.Further investigations were proformed to determine the mechanism of interaction between biothiols or Hg²⁺ and DNA-Ag NCs.The main results are as follows:?1?The single-stranded DNAs?ssDNA?were employed as capping scaffolds for the formation of fluorescent DNA-Ag NCs.The optical properties of these different DNA-Ag NCs were studied by the methods of UV-Vis spectroscopy,fluorescence spectroscopy and so on.The results showed that there were different fluorescence properties of DNA-Ag NCs formed by the different DNA templates.Finally,the B-DNA was chosen to form Ag NCs to the flowing assay due to the strong red fluorescence and good stability of B-DNA-Ag NCs.?2?We have sensitively detected the biothiols and the activity of acetylcholinesterase?AChE?based on the B-DNA-Ag NCs as a fluorescent probe.The cysteine?Cys?and glutathione?GSH?could be detected by the proposed method as low as 0.134 ?M and 0.172 ?M,respectively,within a good linear range from 0 to 5.0 ?M for Cys,and 0.5 to 4.5 ?M for GSH.Furthermore,the activity of AChE also could be indirectly detected based on the fluorescence quenching of the B-DNA-Ag NCs.The proposed method could also detect the activity of AChE in the range from 0 to 4 U/L,with a detection limit of 0.071 U/L.In addition,the possible fluorescence quenching mechanism was further studied as the following.Firstly,the results of UV-vis showed that there might be a new nonfluorescent complex between the sulfhydryl of biothiols and the silver atom?S-Ag?of DNA-Ag NCs,whichsuggested that static quenching mechanisms were occurring.Secondly,the results of transient fluorescence showed there was dynamic quenching mechanism.Furthermore,the results of TEM showed that DNA-AgNCs were aggregated into the large nanoparticals that are nonfluorescent.More importantly,the proposed method was used to detect the biothiols in the urine.?3?DNA-templated silver nanoclusters could detect Hg²⁺ based on the quenching fluorescence of DNA-Ag NCs.The proposed approach high sensitively detected Hg²⁺ as low as 4.5 nM,within a good linear range from 0to 150 nM.The fluorescence intensity of DNA-Ag NCs was quenched significantly in the presence of Hg²⁺,the possible fluorescence quenching mechanism between Hg²⁺ and DNA-Ag NCs was further studied as the following.On the one hand,the results of UV-vis showed that there might be a new nonfluorescent complex between Hg²⁺ and DNA-Ag NCs,on the other hand,the results of transient fluorescence and steady-state fluorescence indicated that the quenching mechanism might be purely collisional for the Hg²⁺ concentration lower than 80 nM,while in the case of higher concentration of Hg²⁺,there were both dynamic and static quenching mechanisms.Furthermore,the results of TEM exclude the aggregation of DNA-Ag NCs.EDTA and NaBH4 was added to the sample containing Hg²⁺and no fluorescence recovery was observed which argued against the metallophilic mechanism.More importantly,this method has also been successfully applied to the detection of Hg²⁺ in the real water samples.Thus,the DNA-Ag NCs detection system is potentially suitable for Hg²⁺ sensing in environmental samples.