Construction And Application Research Of Fluorescence Sensor Based On MnO₂ Nanosheets And Cu-In-S/ZnS Quantum Dots

Biomolecules have direct or indirect effects on organisms,so their quantitative detection plays an important role in the clinical diagnosis and treatment of diseases.With the rapid development of science and technology,researchers have discovered the analytical method of fluorescence sensing,which has attracted more and more attention because of its advantages of simple operation,rapid,efficient and sensitive analysis.Manganese dioxide two-dimensional nanosheets have a wide and strong absorption band in the uv-vis region and can be used as an effective quencher in the fluorescence sensor.Semiconductor nanocrystalline quantum dots(QDs),as a new type of fluorescent nanomaterials,have unique and superior optical properties,such as high quantum yield,univariate excitation multivariate emission,and photobleaching resistance.In recent years,the application of fluorescent QDs nanomaterials in the analysis and detection of biomolecules has also led to the development of medicine and biological related fields.So,we have prepared environmentally friendly Cu-In-S/ZnS QDs,good-performance manganese dioxide nanosheets and other materials.These nanomaterials have been applied to construct several highly efficient,fast and sensitive fluorescent sensors for sensing DNA,ascorbic acid(AA),and dopamine(DA).This work has potential application value in medical and food safety fields.The main contents of this thesis are as follows:1.Using successfully synthesized MnO2 nanosheets,we have designed a fluorescence resonance energy transfer(Fluorescence resonance energy transfer,FRET)sensing scheme based on MnO2 nanosheets and DNA(MnO2 nanosheets-DNA)probes for high selectivity and sensitivity detection of target DNA(T-DNA).Since the absorption peak of MnO2 nanosheets is overlaped with the emission peak of the fluorescent dye FAM labeled DNA probe(P-DNA),MnO2 nanosheets have a high fluorescence quenching ability.The MnO2 nanosheets and P-DNA can be used as fluorescence receptor and fluorescence donor to occur FRET,resulting in the fluorescence quenching of P-DNA.When T-DNA was added to the reaction system,the P-DNA was detached from the surface of the MnO2 nanosheets,thus inducing the fluorescence recovery of the P-DNA.The FRET biosensor we constructed not only has high analytical performance for target DNA detection,such as a wide linear range(3.90-155 nM),a low detection limit(1.56 nM),but also has excellent specificity and good reproducibility.Moreover,we used the constructed FRET biosensor to detect the T-DNA in human serum samples with high selectivity and sensitivity,thus demonstrating the feasibility of this biosensor in practical biological analysis2.The fluorescence "on-off" biosensor for ascorbic acid detection based on the probe of Cu-In-S/ZnS QDs-MnO2 nanosheet was constructed.Low toxic ternary Cu-In-S QDs,zinc sulfide shell was coated on quantum dot by a hydrothermal method to prepare Cu-In-S/ZnS core/shell QDs with good fluorescence properties have been prepared.Inspired by the reported method,we developed a novel Cu-In-S/ZnS QDs-MnO2 nanosheet fluorescent probe for facile,rapid and low-cost detection of ascorbic acid.The detection principle of this method was illustrated as follows:after adding MnO2 nanosheets to a certain concentration of Cu-In-S/ZnS QDs to form Cu-In-S/ZnS QDs-MnO2 probe,the fluorescence of the Cu-In-S/ZnS QDs was greatly quenched.When we added the reductant AA to the Cu-In-S/ZnS QDs-MnO2 probe,the MnO2 nanosheets were reduced by AA,resulting in the decomposition of the probe,and the fluorescence of the Cu-In-S/ZnS QDs recovered significantly with the increase of the AA concentration.The fluorescence sensor showed a good linear relationship 0.012-2.4 mM(correlation coefficient R2=0.9964)and the detection limit was as low as 2.49 ?M.Notably,this fluorescence sensor was successfully applied to the analytical determination of AA in human serum.3.We have designed a method for the determination of DA based on the inner filter effect of aggregation-induced AuNPs on fluorescence of Cu-In-S/ZnS QDs.The fluorescence of the Cu-In-S/ZnS QDs can be quenched by the AuNPs through inner filter effect(IFE).Since the amine groups of DA are easily adsorbed on the AuNPs surface,aggregation occurs in the presence of DA,and then the hydrogen bond interaction between adjacent DA leads to the cross-linking aggregation of AuNPs,which can effectively promote the fluorescence recovery of the Cu-In-S/ZnS QDs.We reasonably believe that IFE process of AuNPs and Cu-In-S/ZnS QDs will be affected by DA,because the IFE process was regulated by aggregation of AuNPs.The linear relationhsip between fluorescence response and the concentration of DA was obtained.This sensor has good analytical performance,such as a wide linear range(15.8-367 nM)and a low detection limit(5.1 nM).More importantly,this fluorescent sensor has been successfully used for the analytical detection of DA in human serum.