DNA Biosensors For The Detection Of Mercury(Ⅱ) And Adenosine

Mercury ions is a very popular toxic pollutant in environment, and can hardly be degradated. Mercury ions can be converted to organic form by methylation in the natural world and concentrated through the food chain, causing accumulation of mercury in human bodies, causing a serious threat to human health. Mercury ions would result in many diseases, such as DNA damage, kidney and liver failure, and brain and neurological damage, increasing risk of myocardial infarction, and so on. Therefore, it is very necessary and significant to detect the mercury ions in environment.In recent years, aptamers have been widely researched and used. Based on the high affinity of aptamer, many biosensors were developed for the accurate and rapid detection of metabolin, DNA, protein and so on. And it is a novel, attractive and hot topic in the current analytical chemistry. The sensors for mercury detection and aptamer-based sensors have been the subjects of the present thesis, the detail materials are summarized as follows:(1)Based on T-Hg²⁺-T configuration for detecting mercury(II)In chapter 2, we developed a highly selective fluorescence sensor for Hg(II) ion detection in aqueous solutions based on the selective binding of Hg(II) ions with a pair of thymine-thymine mismatch. The sensor consists of two DNA probes functionalized with a fluorophore (fluorescein, F) and a quencher (tetramethyl rhodamine, Q) moiety separately. We investigated and optimized experimental variables including the temperature of hybridization and interference ions. The results showed the biosensor has good selectivity, and the linear range covers 100 to 500 nM, and the limit of detection (LOD) is 79 nM.In chapter 3, a novel electrochemical biosensor for the determination of mercury ions in aqueous solution has been reported. The sensing substrate with a layer of gold nanoparticles on the gold electrode surface was formed through 1,6-hexanedithiol treatment, which could enhance the surface loading of capture probe and improve the electron transfer performance. Another DNA probe used as mercury ion specific binding probe hybridized with capture probe. In the presence of mercury ions, the easy formation of thymine-Hg²⁺-thymine structure destabilized the hybrid complex and caused mercury ion specific binding MSB probe released from the interface. As the result, the amount of electroactive indicator methylene blue adsorbed by the remained DNA on the electrode surface decreased, leading to the decrement of the current signal. Therefore, the change of the redox current could reflect the concentration of the analyte. A linear relationship between the current signal and the logarithm of the target concentration up to 500 nM was obtained, with a detection limit of 0.3 nM. The fabricated sensor is shown to exhibit high sensitivity, desirable selectivity and excellent application in real sample analysis.(2)Aptamer-based fluorescence biosensor for the adenosine detectionIn chapter 4, based on the high affinity and selectivity of aptamer and taken adenosine as a model analyte, we developed a novel, sensitive and selective fluorescence biosensor. Two kinds of nano materials were used in this method, one is the aptamer-labelled magnetic nanoparticle, one the is DNA probe P1 labeled gold nanoparticle. The presents of adenosine would induce the aptamer configuration changing and the displacemnent of the gold nanoparticle. Subsequently, the released gold nanoparticle would catalyze the reduction of copper ions to copper, at gold nanoparticle surface. It would restrain copper ions quenching the fluorescence of calcein, the signal of fluorescence intensity would increase sharply. The result showed adenosine can be deteced from 1.0×10^-11 to 1.0×10^-9 M, with the detection limit 1.0×10^-12 M.