Construction Of Fluorescence Sensors Based On Metal-organic Frameworks And Application For Tea Detection

Tea has been widely researched owing to its high content of minerals,amino acids and tea polyphenols,which are beneficial to human health and disease prevention.The detection of minerals,amino acids and tea polyphenols may always rely on large-scale instruments.Although these methods have high accuracy,but it inevitably suffered from complex preprocessing and professional operation,which would limit the development of these methods.Tea was popular among consumers because of its nutritional and unique flavor.Therefore,it is vital of importance for discrimination of tea categories and tea quality evaluation which was strongly associated with the price of tea.Fluorescence metal-organic frameworks(MOFs)have been widely exerted for identification of different substances as a new sensor material owing to their excellent properties.In this paper,fluorescence Y-MOFs were utilized for F ions detection in tea.Based on Tb(?)and Eu(?)doped Zr(IV)MOFs,the fluorescence sensor array was used for Chinese green tea discrimination according to difference in tea polyphenols.Eventually,the discrimination of Chinese tea according to difference in organic molecules using fluorescence sensor array based on Ln-MOFs(1-3)was established.The specific work is as follows:In this study,rare-earth metal-organic frameworks(RE-MOFs)was successfully designedandpreparedwithananosheetsmorphology.4,4,4,4-(Porphine-5,10,15,20-tetrayl)tetrakis(benzoic acid)(called“TCPP”)as the porphyrin-based planar ligand and Y(?)as the metal center were applied to form the Y-TCPP MOF nanosheets(YTMNs)via coordination chelation.Giving the credit to the distinctive host-guest response between YTMNs and F^-,a fluorescence sensor was developed for F^-sensing.F^-reacted with YTMNs and light-up the fluorescence of YTMNs under the p H of 6.Thus,YTMNs was exploited as a fluorescence nanoprobe for F^-detection with high sensitivity and selectivity.Additionally,the practicability of YTMNs nanoprobe was confirmed by determination of F^-in Chinese green tea(Biluochun).A facile and rapid fluorescence sensor array based on Tb(?)and Eu(?)doped Zr(IV)metal-organic frameworks was proposed for Chinese green tea discrimination.According to large porosity of Tb@Ui O-66-(COOH)₂ and Eu@Ui O-66-(COOH)₂,phenolic hydroxyl groups of tea polyphenols could coordinate with free carboxylic acid groups and was captured into the pores,which led to the disturbance of electronic structure of ligand and inhibited the energy transfer efficiency from ligand to Tb(?)and Eu(?)center,causing the fluorescence quenching effect.Based on Hierarchy Cluster Analysis(HCA)and Linear Discrimination Analysis(LDA),the fluorescence sensor array was employed for successful tea polyphenols classification through the analysis of different fluorescence quenching effect to tea polyphenols.Green tea samples within different types and concentrations were also successfully discriminated using this assay according to tea polyphenols,providing a new method for Chinese green tea identification.Efficient fluorescence sensor array based on Tb(?)and Eu(?)mixed lanthanide metal-organic frameworks(Ln-MOFs)was presented for Chinese tea differentiation.First,organic ligands acted as“antenna”to transfer energy to Tb(?)and Eu(?)after the addition of organic molecules(tea polyphenols and amino acids)into Ln-MOFs(1-3)based on an“antenna effect”,which caused different fluorescence change.Then,Ln-MOFs(1-3),which had multiple fluorescence characteristic peaks at 365 nm,490nm,546 nm,592 nm and 616 nm that could offer multichannel analysis to those analytes.Herein,it could provide an intuitive fluorescence signal change at those fluorescence peaks according to host-guest interaction and fluorescence energy transfer.After the analysis of different fluorescence response of Ln-MOFs(1-3)to five tea polyphenols and main eleven amino acids in tea leaves based on Hierarchy Cluster Analysis(HCA)and Linear Discrimination Analysis(LDA),fluorescence sensor array was able to discriminate them with accuracy.Besides,Chinese tea samples with different categories and grades were also successfully distinguished,confirming the practicality of proposed fluorescence sensor array.In summary,the proposed fluorescence sensor array provided a new method for discrimination of Chinese tea and has potential to monitor the quality of tea related products.