Fluorescence Sensor Based On Carbon Dots And Metal Organic Framework For Ratiometric Colorimetric Dual-mode Detection Of Tetracycline In Animal Food

Tetracyclines（TCs）in animal foods are among the most widely used antibiotics for human health treatment and animal disease control.However,excessive accumulation of tetracycline antibiotics in animal-derived foods and the food chain due to their abuse in animal feeding poses a serious threat to public health.The development of accurate and sensitive detection methods for tetracycline antibiotics are of great importance for food safety and human health.The traditional detection methods of tetracycline antibiotics have the disadvantages of expensive instruments and complicated and strict analysis steps.Therefore,the development of simple and convenient,high sensitivity and high selectivity detection techniques for tetracycline antibiotics is of great significance for monitoring tetracycline antibiotic residues in livestock products.Optical sensors based on fluorescence method have shown broad application prospects in the field of food safety detection due to their simple signal platform,sensitive response,simple operation and low cost.The detection method using fluorescent nanomaterials as signal transduction is widely used in food safety detection due to its excellent light stability,multi-fluorophore and easy functionalization.Carbon dots（CDs）,as a common fluorescent nanomaterial,are often used in fluorescence detection due to their excellent biocompatibility,tunable emission,and good water solubility.Metal-organic framework（MOFs）materials have great potential in antibiotic detection due to their excellent characteristics such as large specific surface area,high porosity,and adjustable structure and chemical composition.At the same time,the excited state energy transfer can change the luminescence emission intensity of their own structure and change the color of MOF,providing a solid basis for fluorescence sensing.In this study,based on the unique properties of CDs and MOFs,fluorescence sensors were prepared for the ratio and colorimetric dual-mode detection of tetracycline（TC）,chlortetracycline（CTC）,oxytetracycline（OTC）and doxycycline（DOX）in animal foods.It includes the following aspects:1.According to the structural characteristics of chlortetracycline including benzene ring and-COOH,monodisperse and uniform double-emission carbon points（D-CDs）were prepared by solvothermal method with 2,5-diamino-toluene sulfate containing benzene ring as carbon source and ethylenediamine rich in-NH₂ as nitrogen source.The aggregation-inducing effect（AIEE）was induced by the formation ofπ-conjugation and hydrogen bond between the-NH₂ of D-CDs and chlortetracycline,which enhanced the fluorescence aggregation and achieved the sensitive detection of chlortetracycline.The optimal detection conditions of D-CDs ratio fluorescence sensor were Tris-HCl(10 mmol L^-1,p H=7.0)buffer,incubation time was 100s,and detection temperature was room temperature 25℃.D-CDs showed a good logarithmic relationship in the concentration range of 0.1-300 nmol L^-1（R²=0.998）,and the limit of detection（LOD）was 7.2 nmol L^-1.The recovery rate was 95.50-104.2%.This indicates that the D-CDs sensor has high selectivity and anti-interference ability for the detection of chlortetracycline.In addition,by extracting RGB values to analyze the fluorescence color change,the dipstick of D-CDs was prepared combined with a smartphone for the visual detection of chlortetracycline,and the LOD was 7.18 ng m L^-1（R²=0.991）.This method has the advantages of high sensitivity and good performance for the detection of chlortetracycline,but it is insufficient for the simultaneous detection of multiple tetracyclines.2.A bimetallic nano sensor was proposed based on the D-CDs dual emission sensor.The abundant-NH₂ makes NH₂-MIL-53（Al）a self-assembly core,and reacts with the-COOH-rich Zn-MOF to form MOF-on-MOF composite structure as a fluorescent sensor for the detection of tetracycline,oxytetracycline and doxycycline.Meanwhile,ratiometric fluorescence sensors with"associated opposite responses"were constructed by coupling the intrinsic fluorescence of tetracycline,oxytetracycline and doxycycline.The LODs of tetracycline,oxytetracycline and doxycycline detected by Zn-MOF-on-NH₂-MIL-53（Al）sensor were 8.24 nmol L^-1,2.77nmol L^-1 and 2.85 nmol L^-1 in the linear range of 0.1-80μmol L^-1.Taking advantage of the advantages of Zn-MOF-on-NH₂-MIL-53（Al）sensor and combining the sensor with a smartphone was constructed for the visual colorimetric detection of tetracycline,oxytetracycline and doxycycline.The LODs were 10.24 nmol L^-1,4.65 nmol L^-1 and 10.73nmol L^-1,respectively.Therefore,this strategy provides a new approach for developing integrated systems for food contaminant detection.In this paper,two dual-emission fluorescence sensors were constructed,which can detect tetracycline antibiotics in animal-derived food products with ratio colorimetric dual mode,and provide a certain theoretical and technical basis for the detection of tetracycline antibiotics.