Upconversion Nanoparticles Fluorescence Sensors For Sensing Main Safety Indicators In Matcha

As the only type of tea that has the functions of drinking,eating and makeup,matcha has been widely used in many fields such as beverage,baking and chemical industry,ushering in unprecedented rapid development opportunities.At present,Chinese matcha tea has no predominant in international market competitiveness.The quality and safety of matcha products are one of the primary reasons for this phenomenon.However,the existing detection technologies still accompany certain limitations in practical application,such as time-consuming,complicated operating and high cost.Therefore,it's necessary to develop more rapid and highly sensitive detection methods for promoting the healthy development of Chinese matcha industry.In the past few years,upconversion fluorescence nanotechnology has attracted more and more researchers'interest due to its special luminescence mechanism,excellent photo-physical properties,high specificity and low-costing,which has been widely used in biological monitoring,drug treatment,material analysis,environmental monitoring and other fields.Based on that,we attempt to combine the detection advantages of upconversion luminescence with the existing methods,focus on the main harmful substances?pesticides,heavy metals and pathogenic bacteria?that affect the quality of matcha,to develop a series of new methods for rapid and highly sensitive detection of harmful substances in matcha.The details are as follows:1.Upconversion fluorescence nano-sensing detection method for pesticide residues in matcha.In view of the problems of traditional detection methods,typical pesticide diazinon was selected as the detection index,and an upconversion nanoparticles?UCNPs?-copper ion-acetylcholinesterase mixed system was constructed for the rapid detection of diazinon in matcha.When diazinon was present in the mixed system,which can inhibit the activity of acetylcholinesterase?AChE?,thereby the catalytic efficiency of AChE reduced and the production of thiocholine also decreased.Thus,UCNPs-Cu²⁺nano-assembly was formed and the upconversion fluorescence intensity of the mixed system decreased.Under the optimal experimental conditions,when the diazinon concentration in the range of 0.1-50 ng/mL,there was a good linear correlation found between the fluorescence quenching efficiency and the logarithmic value of the diazinon concentration,with a detection limit of 0.05 ng/mL.At the same time,the proposed method was also used to detect diazinon in adulterated matcha samples with the recovery rate noted in the range of 96.4%-102.5%,relative standard deviation in the range of 2.1%-3.9%.Furthermore,this method and the GC-MS method were used to detect diazinon,and the results has no significant difference.The study proves that the proposed method can be used for the rapid detection of diazinon residues in matcha.2.Upconversion fluorescence nano-sensing detection method for heavy metal ions in matcha.In view of the limitations of the existing methods for heavy metal ions detection in matcha,typical heavy metal lead ions was chosen as the detection index,a UCNPs-cysteamine-gold nanorods mixed system was constructed to achieve rapid detection of lead ions in matcha.When lead ions was present in the mixed system,the complexion between cysteamine and lead ions will cause the UCNPs to be separated from the gold nanorods,and induce the fluorescence signal of the mixed system to reactivate.Under the optimal conditions,there was a good linear relationship between lead ions in the concentration range of 1-100?M and the relative fluorescence intensity,with a detection limit of 0.5?M.At the same time,the proposed method was also used to detect Pb²⁺in adulterated matcha samples with the recovery rate was noted in the range of 93.99%-102.16%,relative standard deviation was noted in the range of 2.4%-7.8%.What's more,this method and ICP-MS method were used to detect Pb²⁺,and the obtained results has no significant difference.The study proves that the proposed method can be used for the rapid detection of Pb²⁺residues in matcha.3.Upconversion fluorescence nano-sensing detection method for pathogenic bacteria in matcha.In view of the disadvantages of the commonly used methods for pathogenic bacteria detection in matcha,typical bacteria E.coli was chosen as the detection index,a UCNPs-aptamer-tungsten disulfide nanosheet?WS₂?mixed system was constructed to achieve rapid detection of E.coli in matcha.When E.coli was present in the mixed system,the specific aptamer will preferentially bind to E.coli,and the conformation of the aptamer will change,causing the donor molecule to dissociate from the surface of WS₂,and the fluorescence signal will be reactivated.Under the optimal conditions,when the E.coil concentration in the range of85-85×10⁷ cfu/mL,there was a strong linear correlation found between the fluorescence intensity difference and the logarithmic value of the E.coil concentration with a detection limit of 17cfu/mL.Furthermore,comparing the detection results of the design method and the plate counting method for detecting E.coli in matcha samples,the study confirmed that the proposed method hold good stability and accuracy,which can be used to detect target bacteria in matcha.