Studies On Novel Fluorescence And Colorimetric Methods Based On Nano-manganese/Iron Oxide

With the rapid development of nanotechnology in recent years,all kinds of nanomaterials with excellent performance have played a great role in promoting the development of optical sensing technology.Nanomaterials based on transition metal elements manganese and iron have many advantages,such as high stability,low cost,easy preparation and strong catalytic activity,and have been widely used in environmental analysis and disease diagnosis.Therefore,three kinds of Mn-based and Fe-based nanomaterials with excellent nano-enzyme activity were synthesized in this paper,and a series of highly sensitive and selective optical sensing methods were developed with ascorbic acid,pentavalent arsenic and sulfur ions as detection targets.At the same time,the application of these methods in real samples was also discussed and analyzed.The following three research works have been carried out:1.Using manganese dioxide nanosheets,a single emission fluorescence analysis method and a single excitation double emission ratio fluorescence sensing method were developed for sensitive detection of ascorbic acid.In the single emission system,the strong fluorescence of calcein at 515 nm can be quenched by Mn²⁺generated by the reduction of manganese dioxide nanosheets by ascorbic acid.The detection limit of ascorbic acid is 45n M by this signal reduction fluorescence sensing method.Single emission fluorescence analysis method has good selectivity for ascorbic acid,and can be successfully applied to the quantitative detection of ascorbic acid in orange juice samples.In the ratio sensing method,manganese dioxide nanosheets can quench the fluorescence of pyronine Y at 565nm through internal filtration,and can also catalyze the oxidation of thiamine to generate dehydrothiamine with strong fluorescence at 440 nm.When manganese dioxide nanosheets were degraded by ascorbic acid,the activities of inner filter effect and oxidase decreased simultaneously.Therefore,the fluorescence of pyronine Y recovered and that of dehydrothiamine decreased.Ascorbic acid can be quantitatively analyzed and detected according to the value of the ratio fluorescence signal F₅₆₅/F₄₄₀ of the system,and its detection limit is 0.1μm.The method was applied to the recovery experiment of ascorbic acid in human serum and orange juice,and the recovery rate was 97.7-101.2%,which indicated that the ratio fluorescence sensor could be used to detect ascorbic acid in complex samples.2.Based on the oxidase-like activity of FeOOH nanoparticles,using o-phenylenediamine as signal probe,a simple and sensitive dual-mode sensing method of fluorescence and colorimetry was established for the detection of As（V）.FeOOH nanoparticles can oxidize o-phenylenediamine in the presence of H₂O₂,and generate 2,3-diaminophenazine with strong yellow fluorescence signal.Meanwhile,the system changed from colorless to yellow,and the absorbance signal is enhanced.When As（V）is adsorbed on the surface of FeOOH nanoparticles,its catalytic activity is inhibited,and its oxidation of o-phenylenediamine is weakened.At this time,the fluorescence and colorimetric signals are weakened at the same time.According to the changes of fluorescence and absorbance signals,the quantitative detection of As（V）can be realized.The detection range of fluorescence sensing method is 0.02-10μm.The detection limit was 11.7 nm;The detection range of colorimetric sensing method is 0.04-5μm.The detection limit is 17.2μm.This dual-mode sensing method has been successfully applied to the determination of As（V）in lake water.The method has potential application value in real environmental monitoring.3.Based on the oxidase-like activity of MnOOH nanosheets,a fluorescence and colorimetric dual-mode sensing method was established for the detection of S^2-.Compared with the previous detection system,the MnOOH nanosheets in this system can oxidize o-phenylenediamine to 2,3-diaminophenazine without H₂O₂.S^2-can oxidize and decompose the hydroxyl manganese oxide nano-sheet into Mn²⁺,irreversibly inhibiting its oxidase activity,resulting in the reduction of 2,3-diaminophenazine,which also reduces the fluorescence and colorimetric signals at the same time.According to the changes of colorimetry and fluorescence signal of the system,the dual-mode determination of S^2-content is realized.The detection range of fluorescence sensing method is 0.5-450μm,and the detection limit is 0.1μm;The detection range of colorimetric sensing method is 1-450μm,and the detection limit is 0.6μm.