Construction Of Ratiometric Fluorescent Probes For MOFs-encapsulated Dyes And Their Sensing Properties

Metal-organic-frameworks,as a class of porous inorganic-organic nanomaterials,have received great attention in analysis due to their tunable nanochannels,host-guest interactions,and good optical properties.It is a very promising sensing material.To date,a large number of MOFs fluorescent sensors for targeted analytes detection have been reported.However,most of the reported fluorescence sensors have a single fluorescence emission signal,which is easily disturbed by environmental factors,and cannot meet the needs of on-site visualization and rapid detection.In addition,the current research on continuous detection probes is rarely involved.Based on this,the ratiometric（RF）fluorescent probe is constructed by introducing fluorescent dye into the pores of MOFs as guest chromophore,and the"continuous detection"probe is designed by combining the fluorescence detection mechanism.At the same time,the advantages of visual test paper and smartphone detection are utilized to solve the above problems effectively.In this study,a series of work was carried out closely around the design of dyes-encapsulated MOFs,and four kinds of fluorescent probe UiO-66-NH₂@EY,Fe-MIL-88NH₂@RhB,Co Zn ZIF@HTD and ZIF-8@EY were designed respectively.The probe could detect the targeted analytes based on the RF fluorescence model through the exclusive target recognition mechanism.The development of the combined identification strategy of the relevant portable test strips and smartphones provides convenient conditions for visual and rapid detection.More importantly,fluorescent probe for continuous detection,especially fluorescent sensors that can recognize three target analytes in tandem,have also been developed in this work.Four high-level research papers have been published on related achievements,and the specific research contents are as follows:（1）UiO-66-NH₂@EY:The dual emission ratiometric fluorescent probe UiO-66-NH₂@EY was successfully constructed by embedding eosin Y（EY）into UiO-66-type MOF by one-step synthesis.The UiO-66-NH₂@EY probe performed RF fluorescence responses to F^-,Cr₂O₇^2-and urea based on hydrogen bonding,energy transfer effect and urease-assisted effect（p H value regulation）.The fluorescence spectrum corresponding to each target was recorded,and a dedicated F^-,Cr₂O₇^2-and urea fluorescence analysis method was established.The probes can effectively identify F^-/Cr₂O₇^2-in the linear range of 0-25μM,with detection limits of 34.7 n M and 22.3 n M,respectively,and have a linear positive correlation with the urea concentration between0-100μM with a detection limit fitted as 62.7 n M.The developed RF probe has specific selectivity for each targeted analyte and high anti-jamming capability,which has high practical application value.The fingerprint development probe prepared based on UiO-66-NH₂@EY solid powder can make a preliminary judgment on the potential poisoning risk of F^-and Cr₂O₇^2-in toxic industries（alloy factories,etc.）.In addition,the probe has also been successfully used for practical detection of complex biological samples(eg,detection of F^-and Cr₂O₇^2-in cells and urea in serum).（2）Fe-MIL-88NH₂@RhB:Thedual-emissionnanocomposite Fe-MIL-88NH₂@RhB was constructed by encapsulating rhodamine B（RhB）into the cavity of Fe-MIL-88NH₂ by a one-step hydrothermal method.Cu²⁺can bond with the amino group of Fe-MOF to effectively quench the fluorescence of Fe-MIL-88-NH₂,thus realizing the fluorescence detection of Cu²⁺.When glutamic acid（Glu）was continuously added to the Fe-MIL-88NH₂@RhB/Cu²⁺system,the hydrogen bonding between Glu and Fe-MOF and the chelation with Cu²⁺resulted in the quenching of Fe-MIL-88NH₂@RhB by Cu²⁺fluorescence was recovered.In this work,the fluorescence response mechanism of Fe-MIL-88NH₂@RhB for the continuous detection of Cu²⁺and Glu was explored in detail,and a RF fluorescence recognition analysis method for Cu²⁺and Glu was established.The detection limits of Fe-MIL-88NH₂@RhB for Cu²⁺and Glu are 4.23μM and 2.58μM,respectively.The RF fluorescent probe has specific selectivity,high anti-jamming capability and sensitivity,and can be used for detection of residual Cu²⁺in reed leaves Cu²⁺.The recoveries were between 97.0%～109.3%,and the relative standard deviation（RSD,n=3）is less than 5%.The experimental results have good repeatability,high accuracy and satisfactory results.In addition,the probe has good cell membrane permeability and can label Cu²⁺and Glu in cells.With the help of molecular logic gates,the probe can monitor the level of Glu in serum,and make a preliminary diagnosis of the development of amyotrophic lateral sclerosis（ALS）through the output signal.（3）Co Zn ZIF@HTD:The red emission fluorescence molecule 10-（diethylamino）[C]-3-hydroxy-5,6-benzodihydrogen[C]oxanthracene（HTD）was encapsulated in the cavity of Co Zn ZIF by one-pot method to obtain Co Zn ZIF@HTD.Pi can effectively enhance the fluorescence intensity of the probe by bonding with Zn in Co Zn ZIF@HTD.When o-phenylenediamine（OPD）was added to the above system,based on the catalytic effect of metallic Co,OPD with weak fluorescence was oxidized to 2,3-diaminobenazine（DAP）.Moreover,the probe fluorescence changed from red to yellow.Subsequently,benzaldehyde（BA）was added into the Co Zn ZIF@HTD/Pi/OPD system,and the yellow fluorescence was effectively quenched.Based on the above excellent fluorescence response mechanism,a specific and high-sensitivity fluorescence analysis method for Pi,OPD and BA was established.The experimental results show that the Co Zn ZIF@HTD exhibits a good linear relationship with the Pi concentration between 0-250μM,and the detection limit is as low as 18.67 n M.The fluorescence response process of the Co Zn ZIF@HTD/Pi system to OPD is divided into two stages.When the OPD concentration is in the range of 0-60μM,the detection limit is 25.37 n M,and while the added OPD concentration exceeds 60μM,the detection limit is 43.26 n M.After detection of Pi and OPD,the newly constructed Co Zn ZIF@HTD/Pi/OPD system could respond specifically to BA with a detection limit of 51.96 n M.In addition,the probe can be used to detect Pi,OPD,and BA in wastewater,with spiked recoveries ranging from 94.3 to 109.7%and relative standard deviation（RSD）less than 5%.The prepared Co Zn ZIF@HTD test paper is also satisfactory for the visual online tandem detection of Pi,OPD and BA in sewage,and the color tone changes can be observed by naked eyes.The results of bioimaging experiments showed that Co Zn ZIF@HTD could be used to label Pi,OPD and BA in cells.（4）ZIF-8@EY:ZIF-8@EY was constructed by in-situ encapsulation of EY in the nano-cage of MOFs by stirring at room temperature.Pi can effectively enhance the fluorescence of the probe through its bonding with Zn in ZIF-8@EY.In view of the energy transfer effect between EY and neutral red（NR）,RF fluorescence changes are generated after adding NR to the ZIF-8@EY/Pi system.Finally,based on the energy reversal effect,the ZIF-8@EY/Pi/NR system responds to heparin（HP）.The specific tandem fluorescence detection mechanism of ZIF-8@EY for Pi,NR and HP was explored in detail,and the probe could achieve specific and high-sensitivity detection of each targeted analytes.A combined method of visual test strips and smart phones（RGB channels converted into digital values）was established for multi-color tandem detection of Pi,NR and HP in wastewater.The detection limits of each target analyte were 0.015m M,0.031 m M and 0.014 m M.The recoveries were between 96.7～107.5%,and the RSD was less than 5%.These results indicate that this analytical strategy can be used for high-sensitivity and rapid detection of relevant target analytes in wastewater.In addition,the probe has good cell membrane permeability and can be used to label Pi,NR and HP in living cells.