Construction Of Functionalized MOF-based Fluorescent Probes And Their Fluorescent Sensing For Trace Toxic And Harmful Substances

With the rapid development of human society,human beings pay more and more attention to physical health,environment and food safety.The accurate detection of toxic and harmful substances in this system is related to human health and well-being,and is a worldwide research hotspot.Therefore,building a highly sensitive,specific,simple,fast,accurate,recyclable,visual,and intelligent fluorescence detection system has very important application value.In this study,the research work is closely focused on the design of functionalized metal organic frameworks(MOFs)probes.A series of fluorescent probes(Eu³⁺@MIL-53(Al),CDs@Eu-MOF,CDs/QDs@ZIF-8,Ui O-66-NH₂/Eu³⁺@MOF-808)with good stability and high luminescent intensity are used for highly sensitive and specific identification of trace toxic and harmful substances(malachite green,biomarkers of anthrax spores,lead ions and phosphate).The research work has improved the sensing performance of fluorescent probes,realized modular intelligent sensing functions such as visual colorimetry,binary smart logic gates,and smart phones,and enriched the theoretical depth of fluorescent sensing technology.The specific recognition mechanism of the fluorescent probe to the target was explored,and diversified actual sample test applications were carried out.Four high-level papers were published in related results,and the main research contents are as follows:(1)An ingenious nanoscale fluorescent sensor derived from Eu³⁺-postfunctionalized MIL-53(Al)(Eu³⁺@MIL-53(Al))was fabricated though a simple and effective approach.Malachite green(MG)effectively turned off the luminescence of Eu³⁺@MIL-53(Al)via fluorescence resonance energy transfer(FRET),thus enabling MG sensing.The fluorescence response mechanism of Eu³⁺@MIL-53(Al)to MG was explored in detail,and a fluorescence analysis method for specific identification of MG was established.The developed probe exhibited instantaneous reusability after being cleaned with deionized water.The fluorescence intensity,quenching efficiency,and crystal structure of the recoverable sensor after five recycling processes were unchanged compared with those of the original sample.Studies have shown that under the optimized conditions,the fluorescence response signal of the probe has a good linear relationship with the concentration of MG in the range of 1?400?mol/L,the limit of detection(LOD)and limit of quantification(LOQ)are 0.057?mol/L and 0.19?mol/L,respectively.The Eu³⁺@MIL-53(Al)probe proved to be a remarkable fluorescence probe for MG with high selectivity,sensitivity,and excellent regeneration capability.The probe can quickly and quantitatively determine the residual MG content in aquaculture water and aquatic products.The spiked recovery of aquaculture water samples and aquatic products ranges from 96.3%to 105.1%,and the relative standard deviation(RSD)is 2.6%to 4.3%,and the result is satisfactory.(2)Anthrax spores pose a serious threat to human well-being and life,so it is highly desirable to develop a rapid,sensitive,and selective quantitative assay of calcium pyridine dicarboxylate(CaDPA)as a biomarker of anthrax spores.Herein,carbon dots(CDs)chelated Eu³⁺-MOFs as dual-emissive ratiometric fluorescent(RF)probe was successfully fabricated by a simple one-pot in situ selective self-assembly synthetic strategy.The blue-emitting CDs was employed as an effective fluorescence reference,while the Eu-MOFs exhibited enhanced red fluorescence signal through the coordination interaction with CaDPA chromophore.The sensing mechanism is attributed to that CaDPA can sensitize Eu³⁺intrinsic luminescence due to the energy transfer from CaDPA to Eu³⁺.What's more interesting is that with the continuous drop of CaDPA,the emission color of CDs@Eu-MOF changes from blue to red.The results revealed that CDs@Eu-MOFs RF probe can detect CaDPA effectively in the range of 8?170?g/L with good linear relationship,and exhibited a remarkable selectivity for CaDPA,the limit of detection(LOD)is 0.66?g/L.The developed RF probe can achieve CaDPA detection in a very short response time(25 s),has an effective self-calibration function,and can perform highly sensitive and selective recognition of CaDPA in water and human serum sample.The recovery rate of standard addition is between 94.0 and 104.7%,and the result is satisfactory.More interestingly,a paper-based probe has also been devised for on-site detection of CaDPA.In addition,CaDPA is used as input signal to construct a binary logic gate device which performs the"off-on"mode.The constructed CDs@Eu-MOF probe can achieve exceptionally rapid,highly sensitive and selective detection of CaDPA,which can further expand the application prospects in environmental and biological analysis.(3)A novel dual-emissive ratiometric fluorescent(RF)probe CDs/QDs@ZIF-8 has been successfully constructed by employing a simple and effective strategy for in situ encapsulating CDs and thioglycolic acid-modified CdTe quantum dots(QDs)into porous MOFs"cage".Blue CDs acts as a stable internal standard emission,the emission color of CDs/QDs@ZIF-8 changes from red to blue with introducing Pb²⁺,fluorescence of probe is quenched because of the binding of Pb²⁺to thioglycolic acid on the surface of probe and e^-transfer from the photoexcited QDs to Pb²⁺ions,color can be recovered after the adding PO₄^3–to CDs/QDs@ZIF-8-Pb²⁺system,which could take away Pb²⁺ions from the surface of CDs/QDs@ZIF-8.The fluorescence response mechanism of CDs/QDs@ZIF-8 to Pb²⁺and PO₄^3–was explored in detail.The detection ranges for Pb²⁺and PO₄^3–are 0.04?60?mol/L and 0.25?50?mol/L,respectively,and the limit of detection(LOD)are 2.35 nmol/L and 9.42 nmol/L,respectively.The dual-responsive colorimetric fluorescence probe was developed for the ultra-high selectivity and sensitivity continuous detection of Pb²⁺(turn OFF)and PO₄^3–(turn ON)in biological samples.The recovery rate of addition is between 94.0%and 106.5%,the relative standard deviation(RSD)is close to 5%,and the results are satisfactory.More importantly,fabricated agar test paper was also successfully applied in visual detection of Pb²⁺and PO₄^3–in real samples,which can implement without instrument-specific calibration.(4)Phosphate plays an important role in a wide range of chemical and biological processes,so the development of a new phosphate optical sensor with high sensitivity,specificity and visual recognition function has important practical significance.Herein,a ratiometric fluorescent(RF)probe and a smartphone-integrated colorimetric test paper sensing platform for assay phosphate was fabricated using hybrid fluorescent Ui O-66-NH₂ and Eu³⁺@MOF-808 MOFs.After continuous addition of phosphate,the blue fluorescence emission of Ui O-66-NH₂ and the red emission of Eu³⁺@MOF-808were regularly enhanced and quenched respectively,and the fluorescence response of the detection platform to phosphate exhibited a clear color change process(red?pink?blue).The reverse fluorescence response mechanism of Ui O-66-NH₂/Eu³⁺@MOF-808 to phosphate was explored in detail.The designed RF probe has high sensitivity and selectivity to phosphate,the fluorescence response signal and the concentration of phosphate shows a good linear relationship in the range of 1?200?mol/L,and the limit of detection(LOD)is 0.087?mol/L.The probe has been successfully used to detect phosphate in serum,tap water and lake water samples.The spiked recovery rate is95.0?110.0%,and the relative standard deviation(RSD)is less than 5%,and the results are satisfactory.More importantly,the probe solution and test paper of the integrated smartphone are converted to digital values through RGB channels and successfully used to visualize semi-quantitative recognition of phosphate.For the solution system,the R/B value and the phosphate concentration displays a good linear relationship in the range of1?20?mol/L and 20?150?mol/L,respectively,and the LOD is 6.5?mol/L.For the test paper,it exhibits the same linear range as the solution system,and the LOD is 8.3?mol/L.The test strip platform has also been successfully used to detect phosphate in serum,tap water and lake water samples.The spiked recovery rate was 92.8?115.0%,the RSD was close to 5%,and the results were satisfactory.In addition,an RF probe and a smartphone integrated fluorescent test paper were developed separately to devise logic gate devices for detecting phosphate.The multifunctional ratio sensing platform integrated by the smartphone furnishes a new strategy and broad prospects for the intelligent online identification of important targets in biological samples and environmental samples.