Novel Electrochemical Aptasensor For Chemical Pesticide Residues Of Agricultural Products

The extensive use of pesticides has effectively solved the problems of crop diseases and insect pests,but many pesticides and their degradation products will remain in various kinds of agricultural products,food,ecological,environment and drinking water.Hence,it may also cause serious problems of food safety and environmental pollution.Although the conventional instrument has been applied for the detection of pesticide residue,it is hard to use widely because it needs professional operators and environment,expensive equipment,and a lot time.The existing enzyme kits and rapid test card detection methods have shortcomings such as low sensitivity,reproducibility,and high cost,so most of them are only used for preliminary qualitative screening of pesticide residues.Therefore,to solve the problems of agricultural products,food safety,environmental pollution,and even the related economic and trade problems caused by excessive pesticide residue,the development of a simple,rapid,accurate and efficient pesticide residue detection method is of great significance.In this paper,two emerging electrochemical sensing technologies,including photoelectrochemical（PEC）technology and self-powered photo-assisted fuel cell（PFC）technology,and aptamers of the corresponding pesticide as recognition element were combined to construct a series of PEC and PFC aptasensors.Furthermore,based on the PEC and PFC feedbacks,a couple of photoactive nanomaterials were selected and prepared for the construction of aptasensors,which were applied in the fast,sensitive,and selective detection of pesticide residues in agricultural products.The main research contents are as follows:（1）The performance of PEC can be improved by modifying the materials of the electrode interface.Pd nanoparticles（Pd NPs）were successfully modified on the surface of Cd S microspheres（Pd NPs/Cd S）by in situ photoreduction method.A visible light inducive PEC aptasensor was constructed with carbendazim（CBZ）aptamer as specific recognition element and Pd NPs/Cd S as the photoactive interface material,which was applied to detect CBZ.The results showed that the ability of Cd S microspheres to capture visible light was enhanced due to the surface plasmon resonance effect of precious metal Pd NPs.At the same time,due to the Schottky junction formed between Pd NPs and Cd S,the Schottky barrier was generated,which inhibited the photogenerated electron-hole pair recombination,so that the PEC performance of Pd NPs/Cd S was significantly enhanced.Specifically,the photocurrent intensity of Pd NPs/Cd S was 7.7 times that of unmodified Cd S microspheres.The resulting steric hindrance prevents prevented the hole sacrificer from contacting the photoactive interface after the aptamer captures CBZ molecules,so the constructed PEC aptamer sensor exhibited a"signal-off"type signal response mechanism to CBZ.The aptasensor showed a detection range of 0.001 nmol L^-1～1000 nmol L^-1 and a detection limit of 0.03 nmol L^-1（S/N=3）with good selectivity and stability,which can be applied to the detection of CBZ residue in lettuce samples.The detection results are consistent with the results of gas chromatography-mass spectrometry（GC-MS）.（2）In addition to the modification of electrode interface materials,developing a new PEC sensing strategy to improve the performance of PEC has been a research hotspot in PEC field.The prepared N-hydroxyphthalimide/blue titanium dioxide（NHPI/B-Ti O₂）nanocomposite was used as the photoactive interface material,and the diazinphosphorus（DIA）aptamer was used as the specific recognition element.A DIA aptaensor was constructed based on NHPI as the hole medium,which enhanced the PEC sensing signal.The experimental results show that the PEC performance of NHPI/B-Ti O₂ nanocomposite is 2.1 times and 2.7 times of NHPI/Ti O₂ and B-Ti O₂ respectively.This was attributed to the existence of a lot oxygen vacancies and Ti³⁺defects in B-Ti O₂,which was conducive to the separation of photogenerated electron-hole pairs.In addition,NHPI as the hole medium can further reduces the recombination rate of electron-hole pairs.Under the optimized conditions,the constructed DIA PEC aptasensor based on NHPI/B-Ti O₂ showed good sensing performance with a detection range of 0.1 nmol L^-1～1000 nmol L^-1 and a detection limit of 0.03nmol L^-1（S/N=3）.Furthermore,it had good selectivity and stability,and could be applied to detect DIA residue in apple samples.In addition,the introduction of organic hole mediator provided a new idea for the development of PEC sensors.（3）The emergence of self-powered dual-electrode system eliminates the need for reference electrode,which has the advantages of implantable,miniaturization and portability compared with PEC sensor.According to the Fermi level matching principle,cadmium sulfide quantum dots/europium-metal organic framework（Cd S QDs/Eu-MOF）and nitrogen-doped graphene/molybdenum disulfide（NG/Mo S₂）were selected and prepared to be used as photoanode and photocathode active materials,respectively.Subsequently,a novel,visible light driven,light-assisted bipolar self-energy supply system was construct.The results show that the maximum output power density of the self-powered system is 104.5μW/cm² due to the sensitization of Cd S QDs to Eu-MOF in the photoanode.A visible light induced bipolar PFC aptasensor was constructed with acetamidine（ACT）aptamer modified on photo anode for ACT detection.With the increase of ACT concentration,the electrical power signal output of the sensor also increased,and the maximum output power(P_max)had a good linear relationship with the logarithm of ACT concentration.The visible light induced bipolar PFC aptasensor exhibited a detection range of 0.5pmol L^-1～1000 nmol L^-1,and a detection limit of 0.17 pmol L^-1,which could applied to detecting ACT residue in lettuce and spinach samples.In addition,the use of dual-photoelectrode can not only improve the utilization of light energy,but also avoid the use of precious metals,which was expected to reduce the cost of sensors.（4）To further improve the accuracy of the detection sensor,according to the Fermi level matching principle,a novel NHPI/cadmium sulfide hollow spheres（NHPI/Cd S HNPs）was prepared by two-step method as photoanode active material,nickel phthalocyanine/Cu₇S₄（Ni Pc/Cu₇S₄）as photocathode active material.Another novel visible light driven bipolar PFC sensing platform was constructed with Atrazine（ATZ）aptamer modified on the photoelectrode,which applied for ATZ detection.The detection mechanism was based that after ATZ molecules were captured by aptamer,the electron transfer on photocathode was hindered,and the output power density of self-powered energy system is reduced.The constructed PFC aptasensor exhibits a"signal-off"type response mechanism,which exhibited a wide linear range of 0.1 pmol L^-1～1000 nmol L^-1 and a low detection limit of 0.033 pmol L^-1,and could be used for the detection of ATZ in grape and tomato samples.The detection results are consistent with those of GC-MS.PEC sensing technology and PFC sensing technology combined with aptamers were successfully used to achieve rapid and sensitive detection and quantitative analysis of specific pesticides,which can also be used for the detection of pesticides in agricultural products,and the reliability of the prepared aptasensors were confirmed by comparing it with the method of national standard detection.