Application Of Aggregation-Induced Emission Materials And Carbon Dots In Fluorescence Sensing Analysis Of Drugs And Impurities

Aggregation-induced emission materials can overcome the quenching effect of traditional luminescent materials due to the aggregation and have great application prospects in the fields of sensors,bioimaging,drug delivery,and therapeutics due to their excellent optical properties.Especially in terms of chemical sensing,fluorescent sensors made of AIE luminescent materials not only have the advantages of simple operation of traditional fluorescent sensors,rapid real-time analysis,and high spatial and temporal resolution.It also has the advantages of simple production,easy modification,good light stability and high signal-to-noise ratio.In recent years,with the development of fluorescence analysis technology,people have begun to devote themselves to developing more convenient fluorescence analysis methods.The visual fluorescence detection method has great application prospects and commercial value because of its advantages such as simple operation,portability,and fast detection speed.According to the change of fluorescence signal,visual fluorescence sensor can be divided into quenching type,fluorescence enhancement type（turn on）,and ratio fluorescence type fluorescence sensor.In this paper,based on AIE materials,carbon quantum dots and and lanthanide fluorescent compounds,the simple,green,environmentally friendly,and inexpensive"quench-on-quench"（on-off-on）type and ratio fluorescence type visual fluorescence sensor were constructed.The main content of the paper is as follows:（1）An"on-off-on"type fluorescence sensor was constructed to detect iron ions(Fe³⁺)and residual sulfur dioxide（SO₂）in traditional Chinese medicinal materials and foods by using the AIE properties of 4,4-stilbene dicarboxylic acid（H₂SDC）.H₂SDC has only weak fluorescence emission in N,N-dimethylformamide（DMF）solution,but can aggregate and emit maximum fluorescence emission in DMF/H₂O（v:v=1:9,p H 4.0）solution with a fluorescent color change from blue to bright cyan.Among the many different kinds of metal ions and anions,only Fe³⁺can quench the fluorescence of the aggregated state H₂SDC through a dynamic quenching mechanism.In addition,using the reducibility of HSO₃^-,the fluorescence of H₂SDC can be restored by reducing Fe³⁺in the H₂SDC-Fe³⁺mixture to Fe²⁺.Therefore,HSO₃^-can be detected based on the change in the fluorescence intensity of the H₂SDC-Fe³⁺mixture.Between the fluorescence intensity of H₂SDC and the concentrations of Fe³⁺were linearly correlated in the concentration ranges of 0.1-1.0,1.0-10.0 and10.0-60.0μM（0.1-60.0μM）,respectively,the fluorescence intensity of H₂SDC-Fe³⁺and the concentrations of HSO₃^-were linearly correlated in the concentration ranges of 1.0-10.0 and 10.0-80.0μM（1.0-80.0μM）,and the detection limits were 18.5 and 38.4 n M（LOD=3σ/s）,respectively.The sensor has an satisfactory recovery rate and relatively small standard deviation in the actual sample detection,and the H₂SDC fluorescence"on-off-on"phenomenon can also be seen under the irradiation of ultraviolet lamps,which indicates that the sensor has the potential to visually detect Fe³⁺and HSO₃^-on site.（2）A ratio fluorescence sensor(Cu NCs-Al³⁺)for the visual detection of chlortetracycline（CTC）was constructed using copper nanoclusters（Cu NCs）with AIE performance.The addition of aluminum ions(Al³⁺)into the Cu NCs solution caused the Cu NCs to aggregate and emit strong red fluorescence,and this was used as the reference signal.At the same time,by adding CTC to the mixture of Cu NCs and Al³⁺,CTC can form a luminescent complex with Al³⁺(CTC-Al³⁺),so the fluorescence of CTC-Al³⁺can be used as a response signal to detect CTC.When the excitation wavelength is 365 nm,Cu NCs-Al³⁺has a strong and stable fluorescence emission peak at 575 nm.After adding CTC,a new emission peak appears at 495 nm,and this emission peak has little effect on the fluorescence emission at 575 nm.Under the best conditions,the concentration of CTC has a good linear relationship with the fluorescence intensity ratio of Cu NCs-Al³⁺(I₄₉₅/I₅₇₅)in the range of 0.1-3.0μM,and the detection limit is 25.3 n M（LOD=3σ/s）.The sensor has good stability and reproducibility and has been successfully applied to CTC detection in environmental water and milk samples.In addition,the fluorescent color of the Cu NCs-Al³⁺mixture can change from red to orange with the increase of the concentration of CTC.Therefore,the sensor has the potential to perform on-site visual colorimetric detection of CTC with the assistance of UV lamps.（3）Carbon dots（CDs）with blue fluorescence were synthesized by a simple hydrothermal method and combined with the Cu NCs-Al³⁺mixture prepared as the previous chapter to construct a ratio fluorescence sensor(CDs@Cu NCs-Al³⁺)for rapid detection of thiamine（Th）.When the excitation wavelength is 356 nm,CDs@Cu NCs-Al³⁺can produce two independent fluorescence emission peaks at 444 nm and 575 nm,respectively.When Th is added to CDs@Cu NCs-Al³⁺,Th can quench the fluorescence of CDs at 444 nm without affecting the fluorescence of the Cu NCs-Al³⁺mixture at 575 nm.Under the optimal conditions,the fluorescence intensity ratio(I₄₄₄/I₅₇₅)of the mixture of CDs@Cu NCs-Al³⁺and Th is linearly correlated in the concentration range of 15.0-80.0μM,the detection limit is 2.63μM（LOD=3σ/s）,and it has good repeatability and stability.In addition,the fluorescent color of the CDs@Cu NCs-Al³⁺can change from purple to red as the concentration of Th is added,and the colour change effect is obvious.Therefore,the sensor has on-site visual colorimetric detection potential for Th with the aid of 365 nm UV lamps.（4）This study utilized ciprofloxacin（CIP）and terbium ion(Tb³⁺)to form a strong fluorescent complex to construct a green-friendly and cost-effective"on-off-on"type fluorescent sensor（CIP-Tb）for continuous detection of copper ion(Cu²⁺)and cysteine（Cys）.CIP can form a green fluorescent complex with Tb³⁺.Due to that adding Cu²⁺,which has a strong affinity to CIP,can quench the fluorescence of CIP-Tb,and then,adding Cys to the mixture of CIP-Tb and Cu²⁺can restore the fluorescence of CIP-Tb,the"on-off-on"mode to visually continuous detection of Cu²⁺and Cys can be realized.Under the optimal conditions,the fluorescence intensity of CIP-Tb is linearly related to Cu²⁺in the concentration range of10.0-200.0μM,and the detection limit is 0.423μM（LOD=3σ/s）.It has a good linear relationship between the fluorescence intensity of CIP-Tb-Cu²⁺and the concentration of Cys in the ranges of 10.0-120.0 and 150.0-270.0μM,and the detection limit is 2.71μM（LOD=3σ/s）.In addition,the fluorescence quenching of CIP-Tb and the fluorescence recovery of CIP-Tb-Cu²⁺can be recognized by naked eye under 365 nm UV lamp,which indicates that the sensor has a potential of visual colorimetric detection of Cu²⁺and Cys with the assistance of UV lamp.