Construction Of Heterojunction-based Photoelectrochemical Sensor And Its Application In Mycotoxin Detection

Photoelectrochemical（PEC）sensor,which is constructed on the basis of electrochemistry,is an analysis and detection method based on the photoelectric conversion performance of photoactive substances and the process of chemical and biological recognition.In PEC analysis,light is utilized to excite the photoactive species and the electrical signal is transduced as the detection readout.Using two separate forms of signal for excitation and detection,the PEC detection method possesses potentially low background,high sensitivity and fast response,and PEC sensing also has the advantages of simple instrumentation,low cost,and easy to miniaturize miniaturization.Therefore,PEC sensor has become a promising analytical method.PEC sensor includes two critical ingredients of photoelectric conversion element and sensing identification unit.The photoelectric conversion element needs to choose a semiconductor material with excellent photoelectric efficiency and stability,sensing recognition unit mainly uses chemical or biological molecule with specificity for target.Through the combination of the two parts can convert chemical or biological information into electrical signal to realize the detection of analyte.However,the individual semiconductor material has low photoelectric conversion efficiency and poor optical stability,resulting in a poor effect of PEC sensor.Fortunately,the heterojunction composites material with energy-level matching can effectively inhibit the recombination of electron-hole pairs,accelerate charge transport,and output stable photocurrent to improve photoelectric conversion efficiency,which can significantly improve the analysis and detection performance of PEC sensor.In this paper,the research began from the controllable synthesis,doping and interface control strategies,and suppressed the recombination of electron-hole pairs,a series of photoelectric functional heterojunction materials with excellent photothermal stability,wide spectrum absorption range and high photoelectric conversion efficiency were developed to construct PEC sensor for the highly sensitive analysis and detection of mycotoxins in food contaminants.The research content mainly includes the following five parts:（1）Construction of CdS/GO heterojunction-based molecularly imprinted PEC sensor for fumonisin B1 detectionIn this chapter,a molecularly imprinted photochemistry（MIP-PEC）sensor was prepared based on CdS/GO heterojunction,which could realize the sensitive detection of fumonisin B1（FB1）.The energy level of CdS QDs matched well with GO is beneficial to the separation of electron-hole pairs and the improvement of photoelectric conversion efficiency.Through the UV-visible（UV-vis）spectrca,electrochemical data and theoretical calculation,the CB/VB of CdS QDs and the LUMO/HOMO of GO were obtained to elucidate the generation,transfer paths of carriers and photocurrent enhancement mechanism.Under optimal conditions,the proposed MIP-PEC sensor was successfully employed for FB1 quantitative determination with a linear range of 0.01 to 1000 ng·m L^-1with a limit of detection（LOD）of 4.7 pg·m L^-1.In addition,the MIP-PEC sensor exhibited an excellent selectivity and stability under high concentrations of interfering substances circumstance,and the satisfactory recoveries in maize solution and milk illustrated the credible application of the proposed MIP-PEC sensors for real samples,indicating a reliability detection in the application of actual samples.（2）Construction of CdS/Pdots heterojunction-based molecularly imprinted PEC sensor forα-solanine detectionIn this chapter,a p-n heterojunction MIP-PEC sensor based on organic polymer dots（Pdots）and inorganic CdS QDs was established for the determination ofα-solanine.Here,a slightly better conductivity of p-type Pdots（p-Pdots）and n-type CdS QDs（n-CdS）were used to form organic-inorganic p-n heterojunctions by layer-by-layer to enhance PEC signal,and their specific energy levels were calculated to study the effect on generation,separation and transfer mechanism of photo-generated carrier and photocurrent enhancement mechanism.The photocurrent change value of the organic-inorganic-based MIP-PEC sensor showed a good linear relationship with the logarithm of the concentration ofα-solanine from 0.01 to1000 ng·m L^-1,and LOD was as low as 6.5 pg·m L^-1.The results show that the method is simple,convenient and sensitive,and it can be used for the detection of ultratraceα-solanine in complex samples.（3）Construction of Cs Pb Br₃/rGO heterojunction-based molecularly imprinted PEC sensor for mycotoxins detectionIn this chapter,a novel peroskite of Cs Pb Br₃/reduced graphene oxide（Cs Pb Br₃/rGO）nanoscrolls heterojunction was prepared by using the self-scroll effect of ultrasonic assisted rGO in an adverse organic solvent,and MIP-PEC sensor was constructed for the detection of aflatoxin B1（AFB1）and ochratoxin A（OTA）.The heterojunction used the more conductive of rGO as the framework and electron transfer medium,and Cs Pb Br₃QDs as the main photoactive substance.By transforming two-dimension（2D）rGO nanosheets into a one-dimension（1D）nanoscrolls structure with a controlled interlayer structure,the rGO NSs had a significantly more accessible inter-wall area to contact the Cs Pb Br₃QDs tightly.Not only this method dramatically improved Cs Pb Br₃QDs stability because of the multilayer nonpolar honeycomb carbon regions of rGO NSs protecting shell,but also the ultrafast interfacial electron and hole transfer of Cs Pb Br₃/rGO NSs enhanced PEC performance due to a matching band-edge arrangement and an efficient electron transfer path.There was a good linear relationship between photocurrent change value of MIP-PEC sensor and the logarithm of two toxins（AFB1 and OTA）concentration from 1.0 pg·m L^-1to 1.0μg·m L^-1,and the LOD of 0.72 pg·m L^-1for AFB1 and 0.67 pg·m L^-1for OTA,demonstrating an excellent analytical performance.Importantly,the detection limit is one order of magnitude lower than that of the previous system,indicating that the material synthesized by this method can effectively improve the sensitivity of the sensor.（4）Construction of N,S-CDs/Cu Pc heterojunction-based molecularly imprinted PEC sensor for ochratoxin A detectionIn this chapter,N,S-CDs/Cu Pc composites were synthesized by nitrogen-sulfur co-doping and copper phthalocyanine（Cu Pc）non-covalent functionalization approaches,and a MIP-PEC sensor was constructed for the detection of ochratoxin A（OTA）.Through the approaches of heteroatom doping and non-covalent functionalization,N,S-CDs/Cu Pc is endowed with an excellent bonding interface and a broad light absorption range.The efficient charge transfer capability and improved photoelectric conversion efficiency of N,S-CDs/Cu Pc were proved by spectroscopic,electrochemical,Mott-Schottky and transient photocurrent tests.The study shows that this synergy contributed enormously to the sensitivity of MIP-PEC sensor,and a linear range of 0.001 to 100 ng·m L^-1for OTA detection with a LOD as low as0.51 pg·m L^-1,indicating that the regulation method can effectively improve the sensitivity of the sensor.（5）Construction of Cu O/Bi OCl heterojunction for photoelectrochemical sensing and photoelectrocatalytic degradation of aflatoxin B1In this chapter,we constructed a novel copper oxide/bismuth oxychloride（Cu O/Bi OCl）composite by in-situ growth of Cu O on Bi OCl surface,which further optimized the heterojunction bonding interface.The photo-absorption region of Cu O/Bi OCl was efficaciously broadened from UV to visible range,making for enhanced light harvest.Meanwhile,the p-n heterojunction in Cu O/Bi OCl clarified that the formed built-in internal electric field could accelerate band-band transfer of carriers.Driven by this,PEC response of Cu O/Bi OCl was greatly boosted comparing with that of pure Cu O or Bi OCl.Further combing with the specific aptamer,a favorable Cu O/Bi OCl-based PEC biosensor was fabricated for AFB1 detection with ultra-sensitivity(LOD of 0.07 pg·m L^-1)and satisfactory recoveries（96.4%～105.7%）in real maize samples.Subsequently,under light irradiation and suitable bias voltage,a degradation rate of～81.3%was facilely attained for 5.0μg·m L^-1of AFB1,indicating excellent photoelectrocatalytic activity of Cu O/Bi OCl material.The catalytic mechanism and the main product of AFB1 degradation were analyzed by ESI-MS and HPLC assays.In conclution,the heterostructured Cu O/Bi OCl-based PEC assay provides a potential way for monitoring and controlling the AFB1 contamination in the food security areas.