Preparation Of 2,4-D Molecularly Imprinted Fluorescence Sensor And Its Application In Fruit And Vegetable Detection

2,4-dichlorophenoxyacetic acid(2,4-D)is a common herbicide of phenoxyacetic acid,which remains in fruits and vegetables,can affect human health seriously when it enters human body.It may cause cancer,endocrine disorders,acute congestion,and degeneration of the central nervous system.Various traditional detection methods,such as high performance liquid chromatography(HPLC),liquid chromatography-mass spectrometry(LC-MS),gas chromatography(GC),gas chromatography-mass spectrometry(GC-MS),microbiology,and immunization methods,etc.,are often cumbersome,long time-consuming,high false positive rate,and usually need expensive equipment,high requirements for sample preparation,besides,their biological antibody stability is poor and the shelf life is relatively short.The molecularly imprinted polymer fluorescence sensor combines the molecular imprinting technique with the fluorescence characteristics of quantum dots to enable highly sensitive and selective detection of 2,4-D,which greatly saves sample preparation time,thus providing a convenient,fast,and stable method to detect 2,4-D.In view of this,we use two different materials,and combined them with quantum dots(QDs)as well as surface imprinting to prepare new 2,4-D fluorescent sensors.The sensors' properties have been examined in detail,and they have been used in the actual detection of food samples.In addition,this paper first tried to introduce the concept of ratio fluorescence into the paper chip system,and attemped to build a ratio-type fluorescent paper chip,which laid the foundation for the future construction of a visual ratio fluorescent microfluidic paper chip.The main research contents and results are as follows:(1)We constructed a novel molecular imprinting fluorescence sensor through anchoring mesoporous structured imprinting microspheres on the surfaces of QDs surface for the sensitive and selective detection of 2,4-D in the light of an electron-transfer-induced fluorescence quenching theory.The obtained sensor was well characterized and had fluorescence properties as well as ideal spherical morphology.Under the optimized circumstance,the sensor showed a satisfactory linearity within 0.66-80 ?M,and the detection limit is 2.1 nM within 20 min.The sensor was successfully implemented for the detecting of 2,4-D in bean sprout samples,and acquired high recoveries at three spiking levels of 2,4-D,ranging from 95.0 to 110.1%,with precisions below 4.9%.By taking full advantage of QDs and surface imprinting,the sensor showed good selectivity and high sensitivity for separating,enriching and detecting 2,4-D in real food samples,thus assuring food safety.(2)By using 2,4-D as a template molecule,quantum dots as a fluorescent material and cellulose paper as a substrate material,a novel fluorescent imprinted paper chip was prepared,which can be used for sensitive detection and specifically identifying 2,4-D,achieving rapidity,portable,economic and other testing advantages.When the 2,4-D solution is dropped on a imprinting paper chip,amino group can form a complex with the 2,4-D,after which the energy of the QDs is transferred to the complex and the fluorescence of the QDs is weakened,thereby realizing the detection of 2,4-D.The test results are satisfactory with a linear range 0.83-100 ?M The detection limit reached 2.6 nM The imprinting factor is 2.13.This study provides a rapid and convenient method for the detection of 2,4-D,which has a great potential for rapid detection in the field.(3)The paper chip constructed in this study uses cellulose paper as a base material.We first modifies the QDs with red fluorescence on the surface by means of chemical catalysis,and then grafts the NBD-C1 molecules with green fluorescence by the coupling method.By detecting different fluorescence peak positions of QDs and NBD,the construction of a ratio-type fluorescent paper chip is realized.The results of this basic research confirm the possibility of constructing a ratio-type fluorescent paper chip.The fast and visual inspection of the individual elements provides new theoretical and technical support,which is of great significance for ensuring food safety.These results enrich the detection methods of 2,4-D.The prepared fluorescent imprinted sensors have high sensitivity and selectivity,and provide theoretical and technical basis for the further study of ratio fluorescent imprinted paper chips.