Construction And Application Of Manganese Dioxide Nanosheets Ratiometric Fluorescence Biosensor

Due to the advantages of high sensitivity,good selectivity,simple operation,real-time detection,and good portability,fluorescence sensing methods have been widely used in many fields such as life sciences,medical imaging,and biosensing analysis.Among them,ratiometric fluorescence sensing strategies could achieve the the analysis of the target by simultaneously measuring two or more fluorescence signals at different wavelengths and calculating their intensity ratios.Compared with the traditional fluorescence methods,ratiometric fluorescence sensing strategies greatly reduces the interferences of many uncontrollable factors on the analysis performance through the establishment of internal reference ratio,such as probe concentration,temperature,solvent polarity,excitation wavelength and environmental p H.It further enables the sensing events of ratiometric fluorescence sensing strategy result in more accurate detection results and wider signal response range.Therefore,in recent years,ratiometric fluorescence sensing strategy have attracted widespread attention in the field of biosensing,and many of ratiometric fluorescence sensors based on new nanomaterials have been developed and applied into the practical analysis and detection of many analytes,especially the ratiometric fluorescence sensing methods with simple operation,high detection sensitivity and excellent selectivity have shown greater potential in practical application.Based on this,a new ratiometric fluorescence sensing method for the simple,rapid and sensitive detection of alkaline phosphatase（ALP）and glutathione（GSH）was designed and developed in this thesis.This thesis is divided into four parts as follows:1.The definition,classification and design principles of fluorescence sensing methods were introduced.The application of fluorescence sensing strategies based on nanomaterials in the field of analytical fields were highlighted and discussed.2.A ratiometric fluorescence sensing strategy for the selective detection of ALP was constructed by using manganese dioxide nanosheets（MnO₂ nanosheets）with excellent oxidation properties and o-phenylenediamine（OPD）as the sensing signal precursor.MnO₂ nanosheets could oxidize OPD to its oxidation product（ox OPD）with a distinct yellow fluorescence at 563 nm.With the addition of ALP,ascorbic acid-2-phosphate（AAP）could be hydrolyzed to ascorbic acid（AA）.The generated AA can further react with OPD to form 3-（dihydroxyethyl）furano[3,4-b]oxyquinolin-1（DFQ）,while this process can be significantly catalyzed by MnO₂ nanosheets in the reaction system,resulting in the formation of a large amount of DFQ with an intense blue fluorescence at 430 nm.The above two fluorescence emission peak intensity ratios(F₅₆₃/F₄₃₀)then were read out as the sensing signals,and subsequently successfully constructing a ratiometric fluorescence sensor of ALP.The results showed that the ALP concentration had a good linearity in the range of 0.25-10 m U/m L with the linear correlation coefficient R²=0.997 and the detection limit of 0.06 m U/m L.The interference experiments demonstrated that the constructed ratiometric fluorescence sensor has good selectivity and anti-interference ability for the analysis of ALP,and can perform sensitive analysis of ALP in the complex serum samples.3.A new ratiometric fluorescence sensing method of glutathione was successful proposed based on the fluorescence quenching effect of MnO₂ nanosheets.The sensitivity of this ratiometric fluorescence sensor was significantly improved by the internal filtration effect（IFE）between MnO₂ nanosheets and the fluorescent polydopamine nanoparticles（F-PDA）,resulting in the highly sensitive quantitative detection of glutathione（GSH）.MnO₂ nanosheets could effectively oxidize OPD to its oxidation product（ox OPD）with unique yellow fluorescence.In addition,MnO₂nanosheets as a fluorescent acceptor could significantly quench the green fluorescence of the F-PDA donor.When the target GSH was added,MnO₂ nanosheets in the reaction system can react with GSH and lead to the reverse change of the intensity of the above two fluorescent signals.With the increase of GSH concentration,the fluorescence intensity ratio of the sensing system showed a good linear relationship with the concentration change of GSH.Based on this,we successfully established a ratiometric fluorescence sensor for GSH with the detection limit low to 1.78M.4.The advantages of the ratiometric fluorescence sensing strategy based on manganese dioxide nanosheets are summarized,and the future directions of such ratiometric fluorescence sensors are also discussed and presented.