| As an important substance in modern agricultural production activities,pesticides have played a considerable role in preventing,controlling,or eliminating crop diseases and pests,improving crop yield and quality,etc.However,excessive or improper use of pesticides will remain in the environment,living organisms,and food,which is a serious threat to people’s health.Therefore,the development of rapid and accurate detection methods for pesticide residues in agricultural products,timely detection of excessive pesticide residues,and illegal use of prohibited pesticides are of great significance to effectively protect people’s"tongue safety".This thesis designed and prepared a variety of new functional nanomaterials as the interface active materials of photoelectric chemical sensors,using corresponding aptamers as specific recognition elements,combined with new electrochemical analysis technologies such as photoelectric chemistry（PEC）and organic electrochemical transistor（OECT）.A series of photoelectric chemical sensing methods for the detection of organophosphorus pesticides were established,which realized the rapid,sensitive and selective detection of organophosphorus pesticides in agricultural products.A series of photoelectrochemical sensors for the detection of organophosphorus pesticides were established,which realized the rapid,sensitive and selective detection of organophosphorus pesticides in agricultural samples.At the same time,combined with the advantages of OECT,the traditional three-electrode system is integrated by laser etching technology to realize the portability of the detection device.The main research contents are as follows:（1）A PEC aptasensor for edifenphos（EDI）detection was constructed using nano-zinc phthalocyanine/molybdenum disulfide（Zn Pc/n-Mo S2）as photoactive material and EDI aptamer as recognition element.The results show that the photocurrent of Zn Pc/n-Mo S2 is 22 and 24 times higher than that of Zn Pc NPs and n-Mo S2,respectively.From the results of electrochemical impedance,UV-visible absorption spectrum and transient fluorescence spectrum,the mechanism of photoelectric enhancement of Zn Pc/n-Mo S2 can be depicted as follows:n-Mo S2 can greatly prevent the aggregation of Zn Pc NPs by anchoring Zn Pc NPs and improve its electron migration rate.Meantime,due to the sensitization of Zn Pc NPs,the carrier lifetime of Zn Pc/n-Mo S2composite is increased by nearly two times under visible light illumination,so that the photogenerated electron-hole pairs are effectively separated,and the recombination rate is greatly reduced.The experimental conditions such as Zn Pc doping ratio and aptamer concentration were optimized.The as-constructed"on-off-on"PEC aptasensor has good sensing performance with a linear range of 5.0×10-9～1.0×10-5 g·L–1 and a detection limit of 1.7×10-9 g·L-1.In addition,the PEC aptasensor has a simple preparation process,good selectivity,and stability,which can be applied to the detection of EDI residues in rice samples.（2）To further enhance the photoelectrochemical activity of the photoactive material and improve the performance of the sensor,molybdenum ditelluride nanoparticles（Mo Te2 NPs）were designed and loaded on reduced graphene oxide nanosheets（RGO）by a one-step hydrothermal method.The experimental results show that the photocurrent of Mo Te2/RGO is 11 and 21 times that of Mo Te2 NPs and RGO,and 8 times that of Zn Pc/n-Mo S2,respectively.The mechanism of photoelectric performance enhancement may be as follows:Due to the existence of the Schottky barrier between Mo Te2 NPs and RGO,the light-generated electrons first pass through the Schottky barrier under visible light irradiation,and then immediately shuttle to the surface of RGO;The presence of Schottky barrier prevents photogenerated electrons from returning to Mo Te2,thus inhibiting the recombination of electron pairs and holes.At the same time,Mo Te2 has a higher carrier lifetime than Mo S2,which further reduces the photogenerated electron and hole pair recombination rate.With Mo Te2/RGO as the photoactive material and PRO aptamer as the recognition element,an"on-off-on"PEC aptamer sensor was constructed and applied to PRO detection with good sensing performance:The linear range was 1.0×10-9 g·L-1 to 1.0×10-2 g·L-1,and the detection limit was 3.3×10-10 g·L-1.The sensor can be applied to the detection of PRO residues in apple and potato samples.（3）To further enhance sensitivity of the PEC sensor,an organic photoelectrochemical transistor（OPECT）aptamer sensor combined with PEC technology and OECT was constructed to detect malathion（MAL）with the prepared Fe-MOF@poly（3,4-ethylenedioxythiophene）（PEDOT@Fe-MOF）as gating material,MAL aptamer as a recognition element,PEDOT:polybenzenesulfonic acid（PEDOT:PSS）as channel material.Comparing the properties of the modified grating pole material PEDOT@Fe-MOF and Fe-MOF,it is found that the former has better electrical conductivity,a larger pore size and a wider visible light absorption range than the latter.Meanwhile,the formation of p-n heterojunction between n-type Fe-MOF and p-type PEDOT can reduce the recombination of electrons and holes in the composites.The photocurrent of PEDOT@Fe-MOF composite is 0.37μA,which is 4 and 23 times higher than that of Fe-MOF and PEDOT,respectively.Under optimized PEDOT doping ratio and aptamer concentration,the linear range of OPECT sensor is 1.0×10-10～1.0×10-5 g·L-1（R2=0.993）,which is wider than that of PEC sensor(1.0×10-10～1.0×10-6 g·L-1).The improvement of OPECT sensing performance can be attributed to that the slight change in the voltage of the gating interface will cause the doping or dedoping of the channel semiconductor,which will result in the sensitive response of the channel current.It can realize the amplification of the photocurrent response by tens or even hundreds of times.This sensor can be applied to the detection of MAL residue in cabbage samples.The OPECT sensor is the combination of a PEC sensor and an OECT amplifier,in which the strategy can be expected to further improve the analytical performance of electrochemical sensors.（4）To further improve the portability of the sensor,this chapter integrates the traditional three-electrode system through laser etching technology.In other words,the gate,source and drain electrodes of OPECT are integrated on the same fluorine-doped tin oxide conductive glass（FTO）chip;Compared with four synthesized functional materials,including Cu-MOF,Cu-MOF modified with Pd nanoparticles（Pd NPs）（Pd/Cu-MOF）,and the corresponding pyrolysis products（p-Cu-MOF and Pd/p-Cu-MOF）.The photoelectric activity sequence is Pd/p-Cu-MOF>p-Cu-MOF>Pd/Cu-MOF>Cu-MOF.This can be ascribed to the p-Cu-MOF with three-dimensional porous structure can support more Pd NPs as an active carrier.Moreover,the REDOX active Cu element can cause electron transfer between the carrier and Pd NPs,thereby regulating the electronic state of the metal active site,improving its catalytic performance and accelerating electron transfer.At the same time,the Schottky junction is formed between Pd-NPS and p-Cu-MOF,which promotes the electron-hole separation.In addition,the pyrolysis of Pd/Cu-MOF not only solves the problem of poor water stability and electrical conductivity,but also the carbon with good electronic properties left after the pyrolysis of MOFs can protect the loaded Pd NPs from aggregation.Furthermore,with Pd/p-Cu-MOF modified gating electrode and ICP aptamer as recognition element,an OPECT aptamer sensor chip for ICP detection was constructed.Under optimized Pd NPs doping ratio and aptamer concentration,there was a good linear relationship between the logarithm of ICP concentration and the intensity of channel current from 1×10-10 g·L-1 to 1.0×10-3g·L-1（R2=0.995）,and the detection limit was 3.3×10-11 g·L-1（S/N=3）.The sensor can be used to detect ICP residue in tomato samples. |
