| Uranium is an ubiquitous radioactive element that exists in a variety of forms in the environment, and the most common valence state in water of uranium is sexavalence. Uranium has been widely used in nuclear weapon and nuclear electric power generation along with the development of science and technology. People have been paid more and more attention to its industrial and commercial use, and at the same time the potential damages brought by uranium are matters of urgent concerns. So it is imperative to build a new economic and fast method to detect uranium.In the chapter 2, a novel strategy for ultrasensitive and selective detection of uranyl by combining graphene oxide-based background reduction with RCDzyme-based enzyme strand recycling amplification in one system was proposed. The graphene oxide is utilized as an adsorbing agent for adsorbing free S-DNA(ss DNA) and free NMM, providing a proximalis zero-background signal in the absence of target. A RCDzyme designed was further employed to amplify the detection signal by enzyme strand recycling and regenerating the RCDzyme to realize enzymatic multiple turnover. The combination of proximalis zero-background signal with RCDzyme-based signal amplification significantly improves the sensitivity of the sensing systems, giving a detection limit down to 86 p M, which is much lower than those of previously reported biosensors. By taking advantage of the highly specific RCDzyme, the proposed strategy showed significantly high selectivity toward target. The assay does not involve any chemical modification of DNA, and has been successfully applied for detecting UO22+ in real samples. In addition, the mechanism of the signal amplification by RCDzyme was demonstrated by CD, fluorescence and UV–vis spectra. We presume that this strategy may be extended to the determination of other analytes by making use of the corresponding DNAzymes for the targets.In the chapter 3, based on both the phenomenon of the fluorescence of NMM being able to be quenched by UO22+ and the specific binding of NMM to G-quadruplex to enhance itself’s fluorescence, a new method for the determination of UO22+ was developed. This method could carry out successfully at room temperature. The linear range of this method was 1.3×10-7 ~7.0×10-6 mol·L-1 with a correlation of r = 0.9994, and the limit of detection was 3.86×10-8mol·L-1. This method was simple with a high selectivity, providing a novel idea for the determination of UO22+.In the chapter 4, the mechanism of the interaction of UO22+ with NMM had been researched by fluorescence and absorption spectra. The results showed that UO22+ can chelate with NMM and quench the fluorescence of NMM, which might be a static quenching process. At the temperatures of 333.15 K, 343.15 K and 353.15 K, the fluorescence quenching constants were 3.06×1013 L·mol-1·s-1, 2.72×1013 L·mol-1·s-1, and 2.40×1013 L·mol-1·s-1, respectively. The linear range of this quenching reaction was 4.9×10-7 ~ 2.4×10-6 mol·L-1 with a correlation of r = 0.9988. It was also found that the quenching effect only tookplace in acid medium with a best quenching efficiency of 42.85% at p H 5.5. This would provide an experimental basis for the following research woks. |
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