Research On Detection Methods Of Tipical Pesticide Residues In Matcha Based On Upconversion Fluorescence Sensing

Matcha is an ultra-fine emerald green tea powder with an extremely high nutritional value that retains its essential components to a great extent.Whether paired with food or brewed independently,matcha is popular among consumers due to its healthy,natural,elegant and convenient features whether it is used with food or served discretely.At present,due to the extensive application of pesticides in the tea planting process,matcha quality and safety concerns affects the competition of China’s matcha industry in the international market.In particular,the safety concern due to carbendazim and paraquat pesticide residues have received an upsurge interest.China,the European Union and United States have regulated the maximum residue limit standards for carbendazim and paraquat in tea.The existing detection technology for pesticide residues in matcha in practical applications suffer from the limitations of long detection time,complex operation steps and high detection costs.Recently,upconversion nanoparticles（UCNPs）have attracted widespread attention because of their special luminescence mechanism,photochemical advantages,and extensive use the field of food testing procedures.Therefore,the current work aimed at developing new methods for rapid and highly sensitive detection of catbendazim and paraquat pesticide residues in matcha based on upconversion fluorescence nanosensing technology.The specific research contents are as follows:1.Carbendazim detection based on upconversion nanoparticles-molecular imprinting.An UCNPs-molecular imprinting detection system（UCNPs@MIP）was constructed by combining UCNPs as the fluorescence support carrier,the template molecule carbendazim and the functional monomer methacrylamide.The fluorescence emission of UCNPs@MIP decreases significantly in the presence of carbendazim via electron transfer induced by its selective binding with MIP cavities.Under the optimized conditions,the developed method obtained a good linear correlation（0.01-1.0μg/m L）,with a limit of detection（LOD）of 0.0036μg/m L for carbendazim residues.The analytical utility and reliability of the developed biomimetic platform were examined in real matcha samples with good recoveries（91.576%～98.340%）and relative standard deviation（RSD）values（0.491%～3.779%）,and validated by standard high performance liquid chromatography（HPLC）with no significant difference.The research findings indicate the applicability of the newly established UCNPs@MIP fluorescence sensor for the rapid detection of carbendazim residues in matcha.2.Carbendazim detection based on upconversion nanoparticles-manganese dioxide nanosheets.The current work was based on the fabrication of aptamer functionalized UCNPs and manganese dioxide（Mn O₂）nanosheets to design an UCNPs-Mn O₂nanosheet composite detection system for carbendazim based on the fluorescence resonance energy transfer（FRET）mechanism.The strong overlap between the absorption spectrum of Mn O₂ nanosheets and the aptamers-UCNPs fluorescence emission,where the later could be self-assembled on the former surface by van der Waals forces to result in fluorescence quenching through the FRET process.In the presence of carbendazim,and its binding with the specific aptamers will culminates the UCNPs-aptamer pair,dropping off Mn O₂ nanosheets and restoring the fluorescence.Under the optimized conditions,a linear calibration plot between logarithmic carbendazim concentration and fluorescence intensity was acquired in the range of 0.1-5000 ng/m L,with a LOD of 0.05 ng/m L.Moreover,the proposed method was also used to detect carbendazim in matcha samples with good recoveries（93.80%-109.40%）and RSD values（1.87%-3.51%）.Additionally,the developed biosensor was validated by HPLC method with no significant difference.Thus,the constructed UCNPs-Mn O₂ detection system can achieve highly specific,ultrasensitive and rapid quantitative detection of carbendazim in matcha.3.Simultaneous detection of carbendazim and paraquat pesticides based on dual color upconversion nanoparticles-black phosphorus nanosheets.In the present work,the aptamer functionalized dual-color UCNPs and black phosphorus nanosheets（BPNSs）were synthesized to construct UCNPs-BPNSs multiplexed detection system based on FRET mechanism.The absorption peaks of BPNSs overlapped with the fluorescence emission peaks of UCNPs,and the reduced distance between aptamer-functionalized UCNPs and BPNSs through theπ-πstacking effect will result in the quenching of upconversion fluorescence due to FRET.When paraquat and carbendazim were added,the aptamer preferentially integrated with their corresponding targets,restoring the fluorescence.Under the optimized conditions,a linear calibration plot between logarithmic pesticide concentrations and fluorescence intensities was acquired in the range of 1.0-1.0×10⁵ ng/m L,with a LOD of 0.18 ng/m L for paraquat and 0.45 ng/m L for carbendazim.This sensor combined dual-color UCNPs,BPNSs’high quenching ability and aptamer’strong affinity.The research shows that the constructed sensor can not only simplify the detection procedure and reduce the production cost,but also achieve ultrasensitive,specific and rapid simultaneous detection of two pesticide residues in matcha.This study established an upconversion fluorescence detection method for pesticide residues in matcha,which provided a reference for the detection of pesticides in matcha.It is of great significance to ensure the rapid development of my country’s matcha industry.