Synthesis And Application Of Surface Molecularly Imprinted Fluorescence Sensors Based On Tetraphenylpyrazine Derivatives

With the development of food industry,the use of food additives is becoming more and more extensive.The addition of an appropriate amount of food additives is conducive to maintaining or enhancing the flavor of food and improving their appearance.However,excessive food additives or illegal use of additives will cause potential risks to human health.Therefore,it is of great significance to develop a simple and fast method to detect food additives.Fluorescence analysis has attracted much attention due to its high sensitivity,easy operation,and high detection efficiency.Combining the fluorescence sensing technology with surface molecularly imprinted technique,surface molecularly imprinted fluorescence sensor can be constructed,which shows broad application prospect in the field of detecting food additives.The use of surface molecularly imprinted fluorescence sensors can avoid complex sample pre-treatment processes since the detection results can be output in the form of fluorescent signals online after specific identification to the target.In this paper,using tetraphenylpyrazine derivative as the fluorescence group,a kind of molecule with aggregation-induced emission（AIE）property,combining the surface molecularly imprinted technique with fluorescence sensing technology,three surface molecularly imprinted fluorescence sensors were synthesized for the detection of rhodamine 6G,brilliant blue and curcumin in actual food samples respectively.The detailed research contents are as follows:1.First,the tetraphenylpyrazine derivative 2,3-di（[1,1’-biphenyl]-4-yl）-5,6-diphenylpyrazine（TPP-M）was synthesized by a two-step method.Its structure and AIE property were characterized.Using vinyl-modified silica nanospheres as the carrier,warfarin sodium,which is a structural analogue of rhodamine 6G,as a substitute template,methacrylic acid as a monomer,and TPP-M as a fluorescence group,a ratiometric surface molecularly imprinted fluorescence sensor（TPP-SMIP）was synthesized by precipitation polymerization for the detection of rhodamine 6G.The composition,morphology and detection ability of TPP-SMIP were analyzed.The experimental results show that TPP-SMIP has a typical shell-core structure,which endow the sensor faster adsorption and elution rates than TPP-MIP,a non-surface molecularly imprinted fluorescence sensor.TPP-SMIP showed a good linear response（R²=0.9988）to rhodamine 6G at a concentration of 0-10.0μmol L^-1,accompanied by a change in fluorescence color from blue to orange-yellow with a detection limit of 2.82 nmol L^-1.Then it was applied to actual samples of pepper and Lianhu water,which were used as the matrix to carry out the standard recovery experiment.The result was also verified by high performance liquid chromatography.Satisfactory recoveries of 95.41%-100.19%and relative standard deviations of 2.24%-6.03%were obtained.These results showed that the detection of rhodamine 6G by TPP-SMIP was successful and reliable.2.Using TPP&SiO₂,which was synthesized by silanization of TPP-M,and CdTe QDs as the fluorescence groups,TPP&SiO₂-MIP with blue fluorescence and CdTe@SiO₂-MIP with red fluorescence were synthesized by sol-gel method.They were then mixed in a certain proportion to construct a molecularly imprinted fluorescence sensor CdTe&TPP@SiO₂-MIP for the detection of brilliant blue.The sensor exhibited two fluorescence peaks at 440 nm and636 nm.When the sensor was combined with brilliant blue,the fluorescence peak at 636 nm was regularly quenched with the increased concentrations of brilliant blue,showing a fluorescence color change from rose red to blue.The ratio of fluorescence intensity showed a good linear relationship（R²=0.9849）with the concentrations of brilliant blue in the range of0-5.0μmol L^-1.The limit of detection was 0.08μmol L^-1.It was subsequently applied to detect brilliant blue in two beverages and spiked recovery experiments.The results showed that the concentrations of brilliant blue in the two beverages were 0.53 and 0.77μmol L^-1,respectively.The recoveries were ranged from 91.83%-98.89%with the relative standard deviations from3.21%to 7.93%.3.Using inorganic material halloysite nanotubes（HNTs）as the carrier,TPP-M and allyl rhodamine B as the dual fluorescence groups,a three-emission surface molecularly imprinted fluorescence sensor（TPP&RhB-SMIP）for the detection of curcumin was synthesized by precipitation polymerization.TPP&RhB-SMIP was characterized by infrared spectroscopy,scanning electron microscopy,X-ray powder diffraction,and surface elemental analysis.The results showed that a molecularly imprinted layer with selective recognition sites was successfully synthesized on the surface of HNTs nanotubes.The optimal synthesis and detection conditions were optimized by adjusting the addition ratio of TPP-M and allyl rhodamine B,testing the detection performance of the sensor in different p H environments and the response time to curcumin.Subsequently,the detection ability of TPP&RhB-SMIP was investigated.After combining with curcumin,the peak of the sensor at 412 nm was quenched while the peak at 585 nm was gradually enhanced.On the other hand,a new peak appeared at 503 nm,which was continuously enhanced with the increased concentration of curcumin.The fluorescence color of TPP&RhB-SMIP showed a change of purple-pink-flesh-yellow with the increasing curcumin.TPP&RhB-SMIP exhibited a good linear response（R²=0.9938）to curcumin in the concentration range of 0-4.0μmol L^-1 with a detection limit of0.16μmol L^-1.It was then applied to detect curcumin in ginger and orange beverages,and spiked recovery experiments were carried out with the actual samples as the matrix.The results showed that the recoveries were 98.97%-110.16%with a satisfactory relative standard deviations of 2.54%-6.69%.