Study On Controllable Synthesis Of Highly Loaded Nanometer Zinc Oxide And Its Being Used On The Electrochemical Detection Of Major Mycotoxins In Fruits

Among crops,especially grain and oil crops,mycotoxins are the most polluted and the most harmful substances,and have been widely concerned.With the improvement of people's living standards,the demand for fresh fruits and their products continues to increase.Fruits are prone to mildew and spoilage and are not resistant to storage,which increases their risk of contamination by mycotoxins.But unlike grain and oil crops,this phenomenon in fruits is often underestimated or ignored.Research reported that patulin?PAT?and tenuazonic acid?TeA?are most harmful mycotoxins in fruits,and widely contaminated the fruits.They pose a threat to the health of humans and animals,therefore it is important to accurately identify and detect them for controlling mycotoxin contamination in fruits.The types and content of mycotoxins in fruits is different with that in grain and oil crops,due to their different main components.In addition,because main components of fruits are pectin and pigments,etc.,the detection range,accuracy,and sensitivity will be affected using the conventional detection technologies.At the same time,the fresh fruits have a high water content,resulting in a low concentration of mycotoxins in terms of fresh weight.Therefore,it is necessary to develop high-sensitivity detection technologies for mycotoxins against fruits and their products.Zinc oxide?ZnO?is a general-purpose semiconductor material,possessing the dual performance of nano-materials and semiconductor materials.It has the advantages of large specific surface area,strong stability,good biocompatibility,easy synthesis,and cheapness.Morphology of ZnO is susceptible to reaction conditions during chemical synthesis.By controlling the influencing factors,they can be prepared with the fixed morphology to meet different usage requirements,which expand the range of application of nanometer ZnO.This study aims to explore the growth rules of nanometer ZnO in hydrothermal synthesis,and compare the loading capacity of nanometer ZnO with different morphologies for biological materials such as aptamers and monoclonal antibodies,then select nanometer Zn O suitable for different mycotoxins and fruits detection environments.Subsequently,a large number of aptamers and monoclonal antibodies are introduced to the electrochemical platform due to their advantages of large specific surface area and good biocompatibility.Finally,the electrochemical sensors for detection of PAT and TeA are constructed based on above considerations.The main research contents and results are as follows:?1?Nanometer ZnO was successfully synthesized by hydrothermal reaction using Zn?NO₃?₂·6H₂O as the source of zinc,NaOH and NH₃·H₂O as the sources of alkali.By changing the conditions such as pH,temperature,reaction time and type of precipitant,the relationship between the reaction conditions and the morphologies of nanometer ZnO was explored,and the controlled synthesis of nanometer ZnO was achieved.The results showed that with the increase of pH and reaction temperature,the morphologies of nanometer ZnO evolved from particles or sheets to rods;and increasing the alkalinity of the precipitant also made nanometer ZnO into rods.Among them,brush-shaped and flower-shaped nanometer ZnO were rough and three-dimensionally arranged.In addition,there was a large number of voids on each monomer surface,so they had a large specific surface area and application potential.The loading capacity of nanometer Zn O for biorecognition materials?PAT aptamer and TeA monoclonal antibody?was studied.The results showed that the PAT aptamer was suitable for loading on the surface of brush-shaped nanometer Zn O,and Te A monoclonal antibody was suitable for loading on the surface of flower-shaped nanometer ZnO.?2?Highly loaded brush-shaped nanometer ZnO was modified on the surface of the gold electrode,and then used it as a loading platform to bind with the PAT aptamer.A three-electrode system was formed by the modified gold electrode as working electrode,calomel electrode as reference electrode and platinum wire electrode as counter electrode.Based on this,the PAT electrochemical aptamer sensor was constructed and applied for sensitivity detection of PAT in fruit products such as apple juice and hawthorn chips.The results showed that the nanometer ZnO-chitosan?ZnO-CS?modification volume on the gold electrode surface was 2?L,the aptamer modification concentration was 8?M,the modification time was 45 min,and the blocking time of the 5%bovine albumin?BSA?solution was 45 min.At this time,differential pulse voltammetry?DPV?was used for detection,and the sensor performance was the best.The PAT sample solution was detected by this method,the detection range was 5×10^-4?g/m L?1?g/mL,the linear regression equation was y=3.10lgC+37.34,R²=0.98,and the limit of detection was 1.51×10^-4?g/mL,the relative standard deviation were 2.51%?5.09%,the average spiked recoveries in apple juice and hawthorn chips were 94.75%?110.84%,for common mycotoxins such as AFB₁,OTA,T-2,ZEN and FB₁,this method has good anti-interference ability.?3?In this study,highly loaded flower-shaped nanometer Zn O was covalently coupled with TeA monoclonal antibody,and then they were co-immobilized on the surface of the gold electrode.The modified gold electrode was used as the working electrode,the calomel electrode was the reference electrode,and the platinum wire electrode was the counter electrode to form a three-electrode system.Then,a TeA electrochemical immunosensor was constructed for detection of TeA in fruits based on large specific surface area of flower-shaped nanometer ZnO to enhance the loading capacity of monoclonal antibodies in electrochemical platform.The results showed that1%thiosalicylic acid?MBA?ethanol solution modified electrode time was 2 h,nanometer Zn O-monoclonal antibody?ZnO-mAb?complex modification concentration and time were 0.8 mg/mL and 2.5 h,the blocking time of 5%BSA solution was 1.5 h.At this time,DPV was used for detection,and the sensor performance was the best.The Te A sample solution was detected by this method,the detection range was 5×10^-5?g/mL?5×10^-1?g/mL,the linear regression equation was y=1.35lgC+25.67,R²=0.99,the limit of detection was 1.14×10^-5?g/m L,the relative standard deviation of the five repeated experiments were 3.05%?6.31%,the average spiked recoveries in tomatoes and citrus were 95.71%?120.30%,this method had good anti-interference ability to the four Alternaria toxins ALT,AME,TEN,and AOH,which were similar in structure to TeA.