Fluorescent Carbon Dots For Essential Components Determination In Food

Food safety is a major issue in global,and it is urgent to develop methods for the determination of active ingredients,nutrients and harmful substances in food.Compared with the conventional analytical methods,the techniques of optical analysis based on nanomaterials have the advantages of simplicity,high sensitivity,easy operation,low-cost,and easily available equipment,etc.As a new photoluminescent nanomaterial,carbon dots(CDs)show the characteristics of being easy to prepare,biocompatible,and easy to be functionalized at surface,etc.,which is a promising material for food qualification.Therefore,the main targets of this research are optical monitoring on food quality.Based on the photoluminescence and catalytic properties of CDs,three sensing system was established for the determination of morin,ethanol content and acetaldehyde in Baijiu,respectively.In particular,the response mechanism in each system was discussed in detail.Five chapters as follows are included in this paper:In the first chapter,the classification of CDs,as well as the synthetic methods,properties of CDs,commonly used methods for food analysis,and in particular,the application of CDs in food determinations were briefly introduced.Accordingly,the key points and research significance of this paper were proposed.In the second chapter,a colorimetric and ratiometric fluorescent,dual-responsive approach was developed for morin determination based on the complexation between CDs and polyethyleneimine(PEI).The CDs were fabricated via hydrothermal method employing tyrosine and malic acid as carbon resource and reductant.Binding with PEI induced an 8-fold enhancement and a slight red-shift to 445 nm of CDs emission.Further morin introduction led to the quenching of CDs-PEI at 445 nm and a generation of yellow emission at 560 nm,which contributed to a ratiometric fluorescence approach for morin determination between 2.0 and 32 μM,with a limit of detection(LOD)of 45 n M.Meanwhile,under sunlight the color of CDs-PEI became yellow upon morin addition,which established a colorimetric method for morin determination in a wider range between 2.0 and 100 μM(LOD = 69 n M).Besides,the developed dual-responsive method either displayed accurate results for morin in diluted human and bovine serum,validating it is potential for actual sample analysis in practice.Finally,a visual approach based on the smartphone was constructed and applied for the real-time determination of morin conveniently.In the third chapter,a fast-responsive fluorescence method was established for ethanol determination in Chinese Baijiu based on the red-emitted CDs.The red-emitted CDs fabricated using p-phenylenediamine(PPD)as the carbon source and citric acid as the reductant,were used for the ethanol determination in Baijiu accuratly.Initially,the PPD-CDs showed a good linear response in ethanol-water solution(E-Ws)in a wide range of ethanol(20-80 vol%),supporting its use for ethanol determination in practice.However,further applying it to Chinese Baijiu resulted in a certain deviation of the fluorescence intensity of PPD-CDs in two systems.After excluding the interference of most ingredients involved,a simple p H correction in Baijiu allowed the PPD-CDs to be used to accurately determine the ethanol concentration in actual samples.In particular,the red emission of PPD-CDs excluded the fluorescence interferences of all intrinsic ingredients of Baijiu,allowing PPD-CDs to be widely applied to various flavor types of Baijiu and further to online ethanol monitoring.Therefore,a fast-responsive fluorescence method was established for ethanol determination in Chinese Baijiu,which not only can be applied to versatile Chinese Baijiu but also has potential for use in other alcoholic beverages.In the fourth chapter,a fluorine-doped carbon dots(d F-CDs)were developed,which process light-activated oxidase-mimic property and high stability at acidic condition.Under the irradiation of 365 nm,d F-CDs generate reactive oxygen species(ROS)to oxidize o-phenylenediamine(OPD)into 2,3-diaminophenazine(DAP).However,further presence of AH can inhibit such processes efficiently,accordingly a dual-responsive method for AH determination was established.More importantly,this dual-responsive method has been applied to the AH determination in different aromas of Baijiu with satisfactory results.The developed strategy in the present study not only provide a multi-mode sensing platform to detect AH in Baijiu,in particular,it extends the CDs application in the field of food science.In the fifth chapter,we summarized the contents of this paper systematically and discussed the perspectives of CDs in the field of food analysis in future.