Design Of The Fluorescent Sensors Based On Inner-filter Effect And Functional Nucleic Acids

The recognition and sensing of the biologically and environmentally important analytes,has emerged as a significant goal in the field of sensor systems in recent years.Several methods have been established,such as high performance liquid chromatography,mass spectrometry,electrochemical analysis and so on.Among them,colorimetric and fluorescence analysis aroused the widest attention.The inner filter effect?IFE?is the main source of error in the fluorescence analysis,but the analytical chemist cleverly use the IFE to transform the absorption signal of the analyte into a fluorescent signal,which improves the sensitivity of the analytical method.The biological macromolecules?DNA?can recognize the target analytes specifically and be synthesized easily with good water solubility and biocompatibility.Therefore,the analytical chemist have designed a variety of fluorescent sensore systems based on functional nucleic acids,Which is highly sensitive and selectivity,nondestructive and suitable for determinations in complex sample.This article summarizes the research progress of fluorescent sensors based on inner-filter effect and functional nucleic acids.The main works are as follow:?1?Combined with literature reports and the preliminary work of our laboratory,as far as we know,this paper first studied the inner-filter effect?IFE?between oxidized 3,3?,5,5?-tetramethylbenzidine?oxidized TMB,oxTMB?and ?,?,?,?-Tetrakis?1-methylpyridinium-4-yl?porphyrin p-Toluenesulfonate?TMPyP?,and a glutathione?GSH?fluorescent sensor system was proposed based on this.In absence of GSH,Ag+ can oxidize 3,3?,5,5?-tetramethylbenzidine?TMB?to form blue oxTMB with an absorption peak centered 652 nm.However,TMPyP has a strong emission speak at 658 nm,significantly overlapping with the absorption peak of oxTMB.Therefore,the fluorescence of TMPyP absorbed by oxTMB would be weak.In the presence of GSH,it could reduce oxTMB to TMB and combine with Ag+ producing Ag+-GSH complex,which results in a decrease of the amount of oxTMB and IFE between TMPyP and oxTMB,turns on the recovery of fluorescence for TMPyP.Under the optimum conditions,the fluorescence intensity F658,responses to the logarithm of GSH over a dynamic range of 0.1-20 ?M,with a limit of detection of 30 nM?S/N=3?.Further application in GSH-spiked fetal calf serum samples suggested a recovery between 95% and 102% and the system is highly selective for GSH over cysteine.?2?Thioflavin T?ThT?can induce G-rich sequence to form a G-quadruplex structure with its fluorescence enhancement.However,as far as we know,there is no report that ThT has induced two G-rich sequences to form split G-quadruplex.In this paper,we first investigated the ability of ThT to induce split G-quadruplex by two G-rich sequences,and a simple label-free turn-on Hg²⁺ fluorescent sensor has been developed based on this.In absence of Hg²⁺,the two sequences is the formation of ssDNA,which interact with ThT weakly.Hence,the fluorescence intensity of system is very low.In the presence of Hg²⁺,the two ssDNA strands prefer to form “T-Hg²⁺-T” dsDNA,which results in the two G-rich segments connecting to each other and forming split G-quadruplex complex.The reporter ThT can be intercalated in G-quadruplex and dsDNA,resulting in remarkable fluorescence enhancement?¹6-fold?.The sensor affords a high sensitivity for Hg²⁺,with a low limit of detection?LOD?of 30 nM based on a calculation of 3?/slope.In addition,the proposed method is also qualified for assessing Hg²⁺ levels in fetal calf serum?FCS?with satisfactory results.?3?Fluorescent dye DAPI can selectively bind to AT-rich dsDNA,NMM can be intercalated in the G-quadruplex with their fluorescence enhancemen.Based on the phenomenon and the specific recognition of mismatched T-T base pair a new two-signal enhanced ratio Hg²⁺ fluorescence analysis method was designed.In the absence of Hg²⁺ in the system,two DNA sequences is the formation of ssDNA,and the fluorescence signal of the system is particularly low.In the presence of Hg²⁺,two ssDNAs form a "T-Hg²⁺-T" double-stranded structure,While the two guanine?G?-rich sequences are close to each other and form a split G-quadruplex structure.Hence,DAPI and NMM are intercalated in the dsDNA and G-quadruplex respectively,resulting in remarkable fluorescence enhancement of DAPI and NMM.At this time,the fluorescence intensity ?DAPI*?NMM,responds to Hg²⁺ over a dynamic range of 0.05-3 ?M?S/N=3?(?DAPI,?NMM are the fluorescence intensity ratio at 455 nm,610 nm in the absence or presence of Hg²⁺,respectively),with a limit of 10 nM,further application in Hg²⁺-spiked fetal calf serum samples suggested a recovery between 98% and 106%,with satisfactory results.