Studies On The Detection Of Mercury And Lead Ions Residues In Water And Food By Non-labeled Fluorescence Sensors Based On Functional Nucleic Acids

With the rapid development of industry,heavy metal pollution in the environment has become an urgent problem to be solved.Even at low concentrations,it may pose a serious threat to human health and the environment because they are non-biodegradable and can be accumulated through the food chain in the environment.Functional nucleic acids are widely used as various recognition sensors in various sensors because of their high sensitivity and specificity.Terbium ion(Tb³⁺)was discovered and utilized as a fluorescent dye capable of being sensitized by single-stranded DNA.Thiazole Orange?TO?,an anthocyanin dye that can bind to a nucleotide to produce fluorescence,especially when inserted into a stable G-quadruplex structure and double-stranded DNA,emits strong fluorescence.In summary,two non-labeled functional nucleic acid fluorescence sensors have been established in this paper to achieve rapid and sensitive detection of lead ions and mercury ions.The main research contents are as follows:?1?A turn-on fluorescence sensor was developed for the label-free determination of Hg²⁺,based on T-Hg²⁺-T coordination and DNA sensitized Tb³⁺luminescence.Single-stranded DNA?ssDNA?greatly enhances the emission of Tb³⁺,but double-stranded DNA?dsDNA?does not.In the absence of Hg²⁺,aptamer hybridizes with the complimentary strand to form the duplex structure in the solution based on Watson-Crick base pairings,which cannot sensitize the fluorescence of Tb³⁺.When Hg²⁺is introduced,aptamer preferentially binds with Hg²⁺to form T-Hg²⁺-T complex due to the powerful affinity of Hg?II?ions to the T bases of the DNA,which releases the complimentary strand.Thus the free complimentary strand can greatly enhance the emission of Tb³⁺,leading the fluorescence intensity to increase dramatically.Under the optimized conditions,the increased fluorescence intensity was proportional to the concentration of Hg²⁺in the range from 8 nM to 500 nM,and this designed method can detect as low as 0.24 nM Hg²⁺.What's more,satisfying results were obtained for the detection of Hg²⁺in river water and fish samples,and the results were in full agreement with those from the inductively coupled plasma mass spectrometry?ICP-MS?.It is taking advantage of fluorescent characteristics of Tb³⁺to observe Hg²⁺,which represents a new opportunity for Hg²⁺monitoring in environment and food.?2?A novel label-free deoxyribozyme-based fluorescent detection method was developed to detect Pb²⁺based on the specific cleavage of the DNAzyme,and the double-strand-chelating dye thiazole orange?TO?.The DNAzyme complex comprises by the hybridization of 17E and 17S strand.When the TO is free,it does not produce fluorescence.But it exhibits strong fluorescence upon binding to DNA,especially double-stranded DNA.In the absence of Pb²⁺,TO will intercalate in the DNAzyme complex,which will produce strong fluorescence.In the prescence of Pb²⁺,it will specifically cleave the ribonucleotide site at 17S,resulting that double-stranded structure is destroyed,so the fluorescence intensity of TO is weakened.Under the optimal experimental conditions,the TO fluorescence intensity decreases with the concentration of the lead ion,and the concentration range is 10-150 nM with a detection limit of 0.73 nM.In addition,the method was successfully applied to the spiked recovery of lead ions in tap water and Songhua River water samples.The results show that the method has good detection performance.And the results of this method are consistent with the graphite furnace atomic absorption method?GF-AAS?,which indicates the reliability of the detection system.Therefore,a method for detecting lead ions that is simple in operation,high in sensitivity,and highly specific is established.