Application Of Quantum Dots And Spiropyran In Fluorescence Sensing Analysis And Detection

Fluorescence analysis has received a widespread attention due to the breadth,simple preparation,low cost,and high sensitivity of fluorescent materials.The detection principle is that the fluorescent probe specifically interacts with the target analyte through electrostatic,hydrogen bonding,coordination,energy conversion,or chemical reaction,and the fluorescence intensity before and after the action will change significantly,so as to achieve the specific detection of target analyte.However,fluorescent probes are susceptible to the interferences from background,instrument fluctuations and operating parameters during use.After continuous exploration,the ratio fluorescent probe can overcome these problems.It realizes the output of the fluorescence signal ratio by introducing multiple fluorescence peaks,which reduces the interference of environmental factors,eliminates some system errors,and improves the reliability of detection.However,for complex components,especially when substances with similar structures and properties are present at the same time,the selectivity of ratio fluorescent probes cannot meet the requirements,so it is very important to increase the selectivity of ratio fluorescent probes.Molecularly imprinted polymers（MIPs）have been widely used in the fields of sample pretreatment and sensor analysis because of their specific recognition performance for template molecules,high stability,easy preparation,and long service life.The composite material obtained by combining MIPs and the ratio fluorescent probe has high sensitivity and high selectivity,so it can be used for the detection of various analytes.Through the continuous efforts of scientific researchers,some fluorescent probes with superior performance have been successfully used in ratio fluorescence detection,such as fluorescent quantum dots（QDs）,metal organic framework（MOF）,photochromic compounds,rare-earth metals,and organic fluorescent dyes.The application of these excellent fluorescent probes,while taking into account the stability and selectivity of the sensor,can shorten the response time,improve the response efficiency,and even have the effect of degrading the detection interferences,which makes it applicable to the detection of actual samples.In this study,several ratio fluorescent probes were constructed based on perovskite quantum dots,MOF,spiropyran,sulfur quantum dots,carbon quantum dots and MIPs,and they were applied to the detection of environmental pollutants,pesticides and disease markers.The main research content of this paper can be summarized into the following four aspects:（1）The construction of MIP-NH₂-MIL-53-Cs Pb（Br I）₃@Asp-Cs₄Pb（Br I）₆ratio fluorescent probe for the fluorescence and visual detection of4-bromophenoxybenzeneFirst,aspartic acid（Asp）as an auxiliary ligand was used to synthesize a core-shell quantum dot Cs Pb X₃@Asp-Cs₄Pb X₆with greatly improved stability.Cs Pb（Br I）₃@Asp-Cs₄Pb（Br I）₆,which emits orange fluorescence,was used as the reference signal,and it was loaded into the fluorescent metal organic framework NH₂-MIL-53 as a detection signal to form a ratio fluorescent probe.In order to improve the selectivity of the ratio fluorescent probe,the surface molecular imprinting technology was further used to wrap the ratio fluorescent probe.The synthetic ratio fluorescent probe MIP-NH₂-MIL-53-Cs Pb（Br I）₃@Asp-Cs₄Pb（Br I）₆was used for the fluorescent and visual detection of environmental pollutants 4-bromo-phenoxybenzene（BDE-3）.The linear range of BDE-3 is 11.4-68.5nmol·L^-1,the LOD is 3.35 nmol·L^-1,and the LOQ is 11.2 nmol·L^-1.The selective recognition experiment shows that this sensor has good specific recognition ability for BDE-3.（2）The construction of a light-responsive ratio fluorescence sensor based on perovskite quantum dots and spiropyrans for the fluorescence and visual detection of thiamethoxamBased on the principle of fluorescence resonance energy transfer（FRET）,a ratio fluorescent probe for the detection of nicotinic pesticide thiamethoxam was developed.We modifiedβ-cyclodextrin（β-CD）on the ultraviolet-responsive molecule spiropyran（β-SP）to block its ultraviolet response ability,while its ultraviolet response ability can be restored after thiamethoxam is added and SP escapes from cyclodextrin.Then after radiation with 365 nm UV lamp,spiropyran can be transformed from its closed-ring configuration（SP）to open-ring configuration（MC）.The MC configuration can accept visible light at about 550 nm and be excited to produce red fluorescence.Therefore,NH₂-Si O₂-Cs Pb Br₃（506 nm）was chosen as its excitation light source and the reference signal,and connected withβ-SP to form the UV-responsive ratio fluorescent probeβ-SP-NH₂-Si O₂@Cs Pb Br₃.The synthetic UV-responsive ratio fluorescent probeβ-SP-NH₂-Si O₂@Cs Pb Br₃was used for the fluorescent and visual detection of pesticide thiamethoxam.The linear range of thiamethoxam is14.4-62.4 nmol·L^-1,and the LOD=4.11 nmol·L^-1,LOQ=13.7 nmol·L^-1.The selective recognition experiment shows that this sensor has a good specific recognition ability for thiamethoxam.（3）The construction of the ratio fluorescent probe MIP-BSQDs-Si O₂@CQDs for the fluorescence and visual detection of carbarylIn the experiments of this chapter,we first synthesized SQDs using a bottom-up synthesis method and doped them with boron（BSQDs）.Compared with SQDs,the fluorescence intensity of BSQDs was greatly improved.Then,based on the BSQDs,yellow CQDs and MIP,using BSQDs as the response signal and Si O₂@CQDs as the reference signal,a molecularly imprinted ratio fluorescence sensor MIP-BSQDs-Si O₂@CQDs was constructed for the detection of carbaryl（CBR）.The results showed that,in the concentration range of 49.7-298.2 nmol·L^-1,there is a good linear relationship between the fluorescence intensity ratio of CQDs and BSQDs and the concentration of CBR.The linear equation is y=0.0033x+0.4055（R=0.997）,and the LOD=14.2 nmol·L^-1,LOQ=47.3 nmol·L^-1.The selective recognition experiment shows that this sensor has a good specific recognition ability for CBR.（4）The construction of a fluorescent probe based on valine-modified carbon quantum for the detection of uric acidIn the experiments of this chapter,we modified carbon quantum dots（CQDs）with valine to construct a fluorescent probe for the detection of uric acid（UA）.The results show that,in the concentration range of 250.0-700.0μmol·L^-1,there is a good linear relationship between the fluoresce-nce intensity of CQDs and the concentration of UA.The linear equation is y=-0.5059+687.3（R=0.9929）,and the LOD=69.42μmol·L^-1,LOQ=231.3μmol·L^-1.The selective recognition experiment shows that this sensor has a good specific recognition ability for UA.