Study On Rapid Determination Of Heavy Metal Ions Based On Aptamer Technology

Heavy metal ions are one kind of main pollutants in the environment,which have caused great threat to human living conditions. With the rapiddevelopment of urban industrialization, life sewage and industry wastewater are drained into water environment. Heavy metal ions can beaccumulated into the human body through the food chain, leading a seriousthreat to people’s health and life. Therefore, it is of great significance toestablish a simple, fast, sensitive method to detect them. Nucleic acids(ssDNA) with advantages of real-time, quick, stable, selective and visualinspection make its broad space to be used in bioanalytical assay,environment monitoring, basic medicine, new drug synthesis or selection. Inthis research paper, new assays to determine the silver and arsenic ions wereestablished based on colorimetric methods. The major contents of this thesisare given in the following．(1) Poly-(diallyldimethylammonium chloride)(PDDA), a cationicconjugated polymer, was used and displays two useful features in thepresent biosensor. One of useful property of PDDA is that it canelectrostatically interact with negatively charged ssDNA strands to form aduplex‘‘structure. Another useful property of PDDA lies in its positivecharge, which can be employed to aggregate citrate-stabilized AuNPs intostable nanochains. First, in the presence of Ag~+, the Ag~+aptamer form stablehair-pin structure through the specific C-Ag~+-C interactions. As a result, theduplex DNA formed in this way cannot interact with PDDA effectively. Thesubsequent PDDA can aggregate AuNPs, which leads to the remarkablechange in color from wine red to blue. However, in the absence of Ag~+, theaptamers are free and can hybridize with PDDA to form a duplex‘‘ structure through electrostatic interaction, thus the subsequent AuNPscannot aggregate owing to the lack of PDDA. Therefore, this strategy makesit possible to detect Ag~+by colorimetric assay, with a limit of detection of48.6nM.(2) Hemin (iron protoporphyrin) is the active center of heme-proteins,which has the peroxidase-like activity similar to the peroxidase enzyme. Inthe presence of hydrogen peroxide, hemin can catalyze3,3′,5,5′-tetramethylbenzidine (TMB) to form a blue charge-transferintermediate and the excess hemin can continue catalytic to form a yellowfinal product. In the absence of As(III) ions, the As aptamer will affect thecatalytic activity through π-π interaction. But, in the of presenceAs(III) ions,the ssDNA can form stable duplex structure through the specific interactions.This duplex structure can‘t absorb hemin and accelerate the formation of theyellow product. With the increase of the added amount of arsenic, thesolution gradually changed from blue to yellow. Therefore, by the colorchange of the solution, the arsenic ions in water can be detected.