Construction And Application Of Fluorescent Biosensor Based On Molybdenum Disulfide Quantum Dots

Fluorescence analysis methods have attracted great attention due to their fast response,simple operation,high sensitivity and selectivity.Fluorescent chemical sensors have been widely used in the detection of various biological molecules.Fluorescent probe is an important part of constructing fluorescent sensors.As an excellent fluorescent nanoprobe,molybdenum disulfide quantum dots?MQDs?have been used to establish a series of fluorescence nanosensors due to their unique optical properties,low biotoxicity,good biocompatibility and water solubility.In addition,compared with single fluorescence system,the ratiometric fluorescence system can effectively reduce the interference of uncontrollable external factors by measuring the ratio of the fluorescence intensity at two emission wavelengths,thereby improving the reliability and sensitivity of the analysis results.In this paper,MQDs were mainly used as fluorescent probes to construct highly sensitive fluorescent biosensors for the detection of various biomolecules using the ratiometric fluorescence strategy.In chapter 1,we mainly introduced the synthesis methods and optical properties of MoS₂ quantum dots and its application in the biomedical field.Finally,the main research contents and significance of this paper were summarized.In chapter 2,we developed a ratiometric fluorescence method for the determination of the anticancer drug 6-mercaptopurine?6-MP?based on the use of MoS₂ quantum dots?MQDs?and horseradish peroxidase?HRP?.In the absence of6-MP,HRP can catalyze the oxidation of o-phenylenediamine?OPD?by H₂O₂ to form fluorescent 2,3-diaminophenazine?DAP?.This led to the fluorescence quenching at415 nm of MQDs,while the fluorescence at 560 nm of DAP became increasingly strong.In the presence of 6-MP,however,it will be preferentially oxidized to form a disulfide dimer.Hence,less H₂O₂ was available for the oxidation of OPD and less DAP would be formed.This resulted in the fluorescence recovery at 415 nm and a fluorescence decrease at 560 nm.Thus,the change in the ratio of the two fluorescence intensities can be used to sensitively detect 6-MP.Linear responses were observed for H₂O₂ in 0.5–140?M concentration range,and for 6-MP in the 0.5–70?M concentration range,with detection limits of 0.1?M and 0.29?M,respectively.The method was sucessfully applied to the determination of 6-MP in spiked human urine with satisfactory results.In chapter 3,we developed a novel and sensitive ratiometric fluorescence strategy for pH sensing and urea detection based on MoS₂ quantum dots?MQDs?and2,3-diaminophenazine?DAP?.The DAP was pH-sensitive and can be used as fluorescence indicator while MQDs was pH-insensitive and acted as a reference fluorescent signal.The fluorescence intensity of DAP at 568 nm exhibited increases gradually while the fluorescence intensity of MQDs at 420 nm kept unchanged as the pH changed from 3.0 to 9.0.So the ratio of the two fluorescence intensities at 568 nm and 420 nm can be used to monitor the change of pH.The pH-sensing system showed a linear and reversible respond to pH in the range of 3.8-6.0 with an interval of 0.2 pH unit.Furthermore,the enzymatic reaction of urea in the presence of urease can lead to the pH increase of the solution,which can be used to detect urea by using the above-mentioned pH-sensing system.There exhibited a good linear relationship between the ratiometric fluorescence intensity of I₅₆₈/I₄₂₀20 and urea concentrations ranging from 5 to 700?M.And a low detection limit of 1.8?M was obtained.The proposed strategy exhibited excellent selectivity and sensitivity.Additionally,the developed ratiometric fluorescence strategy was successfully applied to detect urea in water samples.In chapter 4,we proposed a sensitive ratiometric fluorescence strategy for the detection of epinephrine?EP?and ascorbic acid?AA?based on the fluorescence resonance energy transfer?FRET?between MoS₂ quantum dots?MQDs?and the fluorescent oxidative polymerization product(P_EP-PEI)of EP in polyethyleneimine?PEI?aqueous solution.The continuous formation of P_EP-PEI can lead to the fluorescence quenching of MQDs at 414 nm while the fluorescence of P_EP-PEI at 522nm gradually increased.The introduction of AA can inhibit the oxidative polymerization process of EP due to the strong reducibility of AA,resulting in the fluorescence recovery of MQDs at 414 nm and the fluorescence decreasing of P_EP-PEIP-PEI at 522 nm.Therefore,EP and AA can be sensitively and accurately monitored by measuring the ratio of the fluorescence intensities at 522 nm and 414 nm.A good linear calibration of I₅₂₂/I₄₁₄ versus EP and AA concentrations were obtained within0.2-40?M and 0.5-40?M,respectively.And the detection limit was 0.05?M for EP and 0.2?M for AA.Furthermore,the developed ratiometric fluorescence method was applied for EP in human urine samples and AA in human serum samples determination with satisfactory results obtained.