Synthesis And Application Of Monomeric Fluorescent Probes For Multi-target Detection

In the current research of fluorescence sensors,most of the probe molecules only have fluorescence signals for a single detector,although such single-signal fluorescent probes have good selectivity and sensitivity for specific analytes,but for structurally similar molecules.The identification detection is often difficult to distinguish.In order to improve the detection range of probe molecules,in this paper,the Schiff base-based probes are used to detect metal ions and further detect biological small molecules such as anions or biothiols through their complexes,thereby achieving multi-target detection of biomolecules.Chapter 1: Introduction.This chapter introduces the common composition and research background of fluorescent probes,and summarizes their analytical detection methods and the working principle of colorimetric fluorescence sensors.The research status of some single probe multiple identification signals for detecting metal ions,anions and optical probe molecules of small biomolecules is listed.Based on this,the main design ideas of this paper are proposed.Chapter 2: As an excellent ligand,the p-dimethylbenzoylamino derivative can form a relatively stable compound with many common transition metal ions,and the ligand compound obtained by the reaction often reaches an anion,a biothiol,etc.Achieve the purpose of secondary testing.Based on the above principle,the p-dimethylaminobenzoyl imidazole dialdehyde fluorescent probe（Compound 1）was synthesized and characterized by nuclear magnetic resonance spectroscopy and other methods.The strong coordination of compound 1 and Cu²⁺ was used to increase the plane rigidity of the molecule and thereby block the process of photoelectron transfer（PET）,the fluorescence is enhanced to achieve the purpose of detecting copper ions.On the other hand,due to the existence of a competitive binding copper ion between the formed 1-Cu²⁺ complex and S^2-,when S^2-is added to 1-Cu²⁺,the binding ability of S^2-is stronger than that of compound 1,and complex 1-Cu²⁺ undergoes disintegration and fluorescence reduction.Cu²⁺ was detected by spectroscopic and naked-eye methods with a fluorescence detection limit of 15 n M,well below the minimum safety standard allowed by the WTO（31.5 μM）.In addition,the complex(1-Cu²⁺)can detect S^2-sensitively,and the color changes from clear yellow to colorless with fluorescence quenching,the fluorescence detection limit is 0.12 μM.We verified the binding process by UV absorption,fluorescence measurement,¹H NMR,mass spectrometry and DFT calculation.The successful application of test paper for the detection of Cu²⁺ and S^2-means that it can be easily and quickly analyzed in actual samples.Chapter 3: In this chapter,based on the previous chapter,p-dimethylaminobenzoyl thiophene dimethyl aldehyde（compound 2）was synthesized by changing the subsequent binding groups and used to detect Cu²⁺ and Zn²⁺.The detection principle is to use the strong coordination ability between S on the thiophene group and N on the Schiff base with metal ions to change the luminescence properties of compound 2 by influencing electron transfer.At the same time,the fluorescence emission signals are adjusted by the different binding ratios of Cu²⁺ and Zn²⁺ to compound 2.The detection of Cu²⁺ and Zn²⁺ is realized based on different fluorescence emission signals.In terms of fluorescence detection,the addition of Cu²⁺ and Zn²⁺ resulted in a significant fluorescent color change of Compound 2 from colorless to green or yellow,respectively,which was highly sensitive to Cu²⁺ and Zn²⁺（detection limits（LOD）= 45 n M and 17 n M）.The results of ¹H NMR titration confirmed that the response of compound 2 to Cu²⁺ and Zn²⁺ was initiated by the interaction of thiophene unit,Schiff base unit and metal ion;fluorescence titration and Job-plot curve proved the complexation of Cu²⁺ and compound 2.The ratio is 1:2,and the complex ratio of Zn²⁺ to compound 2 is 1:1.In terms of application,in order to more conveniently detect copper and zinc ions in the environment,a fluorescent test strip is prepared,which means that the detection can be more conveniently and quickly performed in an actual sample.Chapter 4: 4-aminoantipyridine derivatives are often used as good substrates because of their stable chemical properties,more coordination sites and less environmental interference.In this chapter,we synthesized a fluorescent probe4-aminoantipyrine-^2-hydroxy-1-naphthaldehyde（compound 3）with AIE characteristics using a derivative of 4-aminoantipyrine.The aggregation of compound 3 by hydrogen bond in water was investigated by scanning and transmission electron microscopy.The properties of molecular luminescence were expounded by the theory of excited state electron transfer.The structural characteristics and fluorescence spectra of compound 4-6 were further explained by molecular hydrogen bond and plane rigidity to explain ESIPT theory.In terms of molecular detection,there was the strong coordination ability between compound 3 and Cu²⁺.When Cu²⁺ was added,the excited state electron transfer intensity of aggregated compound 3 was changed,and fluorescence quenching occurs.Due to the specific binding between Cu²⁺ and Cys,the constructed complex Cu-3 system has a specific detection of Cys,accompanied by a certain degree of red shift,and the detection limit was 84 n M.Its good biocompatibility made the complex Cu-3 finally successfully applied to Cys imaging in Min6 cells.Its AIE characteristics overcome the problem of low fluorescence efficiency of traditional probes at high concentration,which can be better realized the efficient application of biological probes.