Construction And Sensing Mechanism Study Of Paper-sensor For Detecting Of Biogenic Amines/Hydrogen Sulfide

The development of globalization has made food safety one of the most important issues that people are focusing on and need to solve.Meat consists of rich proteins,fats,minerals,etc.It is one of the main sources of nutrients for people’s life intake.During storage and transportation of meat,proteins were easily exposed to the action of microorganisms to produce substances such as biogenic amines and hydrogen sulfide,which seriously threatened human health and life safety.The cellulose,as the largest stock of biodegradable materials on earth,had the advantages of non-pollution,renewable and environmentally friendly,etc.By loading fluorescent probes on it,fluorescent paper sensors could be prepared that were visual,environmentally friendly and portable,which was useful for expanding cellulose’s application fields.In addition,fluorescent paper sensors were highly popular for their convenience,high sensitivity,selectivity,visualization,and cheaper price,and had been widely used in the fields of medicine,food,and environment.The importance of sensor construction was to design the molecular structure of the fluorescent probe which is based on the chemical properties of the analyte.Based on this background,a series of novel reactive fluorescent probes were synthesized in this dissertation using photochemical theory and organic synthesis,followed by loading the fluorescent probes onto test paper for meat freshness detecting,which provides a reliable means of rapid visualization and detection of meat on site.The main research work includes the following points:（1）Construction of biogenic amines（BAs）turn-on fluorescent test strips and study of their sensing mechanism.In this paper,a series of fluorescent probes（RFCC,RFCB and RFCH）were constructed for the detection of BAs,using resorufin as the fluorophore and ester group as the recognition site.The probe reacted with BAs in a nucleophilic substitution reaction,exposing the pink and red fluorophores resorufin.Due to the spatial site resistance of the masking group leaded to the reaction rate RFCC>RFCB>RFCH.Among them,the fastest responding RFCC showed a response time of 15 min,detection limit（89 n M）,and very obvious color and fluorescence for BAs.The sensing mechanism might be due to amminolysis of RFCC to release resorufin dye,which was confirmed by ¹H NMR and HR-MS.Furthermore,RFCC probes loaded on test paper were used for in situ visualization to monitor the freshness of the seafood.Compared to conventional instruments,the fluorescent paper sensor had low background,fast response and visualization and provides an inexpensive and portable tool for on-site visual monitoring of seafood freshness.（2）Ratio-based two color fluorescent test strips for detection of BAs were constructed and their performance tuned.In order to detected BAs specifically and with high sensitivity,a series of ratiometric fluorescent probes with different recognition sites were constructed in this paper,which use benzothiazole as the fluorophore.By adjusting the number of reaction sites of the probe,the selectivity,response rate and fluorescence color of the fluorescent probe could be adjusted.BTH with dual reactive sites displayed a distinct ratiometric fluorescence color change（red to green）,high sensitivity（70 n M）,response time（<15 min）,and high selectivity for cadaverine（Cad）.The BTH test strips was used to detect Cad vapor.As the concentration of Cad vapor increases,the color of the test paper gradually changes from red to green,which can be clearly identified by the naked eye.The fluorescent strip successfully monitored the freshness of meat at different temperatures,providing a simple tool for on-site visualization and monitoring of meat freshness.（3）Construction of multicolor fluorescent probes for the study of their sensing properties and conformational relationships.A series of fluorescent probes（BDP,BTH,RFCC,CN-NBD,RDE-B）were developed for the detection of Cad,NH₃ and H₂S produced during food spoilage.The spectral response of fluorescent probes to Cad,NH₃and H₂S was explored.The molecular structure and molecular mechanism of the probe before and after its reaction with the analytes.Properties such as sensitivity,selectivity,linear relationship,color and fluorescent color of the probes were examined for the relationship between the structure and performance of the probes.To provide a theoretical basis for the feasibility of cellulose-based optical sensing arrays.（4）Construction of colorimetric and fluorescent sensing arrays.Five fluorescent probes（BDP,BTH,RFCC,CN-NBD,RDE-B）were constructed to study the optical responses of Cad,NH₃ and H₂S produced by meat spoilage,respectively.Cross-responsive cellulose-based sensing arrays were prepared by loading probes individually on test papers,which enabled rapid and correct identification of（0–120 ppm）food contaminants Cad,NH₃,and H₂S vapors.The array combined with pattern recognition maps can be used for colorimetric and fluorescent identification of freshness levels（fresh,slightly spoiled,spoiled,and severely spoiled）,providing an effective means of portable,rapid,non-destructive visual monitoring of seafood freshness.In this work,a series of cellulose-based fluorescent sensors were successfully constructed by molecular fluorescence technology based on the molecular characteristics of biogenic amines or hydrogen sulfide.It provides an experimental foundation for cellulose materials in the field of food contaminant detection,and at the same time provides a scientific basis for the deep development and application of cellulose fluorescent materials.