Construction Of Magnetically Controlled Aptasensor Based On Fe₃O₄@MoS₂ Nanocomposite For Mycotoxin Detection

Consumption of food contaminated by mycotoxins will pose a serious threat to human health,therefore,accurate and rapid detection of mycotoxins has significant theoretical and practical application value.Traditional detection methods have limitations such as cumbersome steps,complicated operations,and heavy reliance on specific large instruments,which cannot achieve the purpose of rapid detection.In this paper,Fe₃O₄@MoS₂nanocomposites were successfully prepared and used as magnetically controlled carriers coupled with nucleic acid aptamer（apt）,a novel molecular recognition element,to construct electrochemical or fluorescent aptamer sensors for the sensitive detection of single-component mycotoxins or the simultaneous detection of two-component mycotoxins.The details of the study are as follows:1.The Fe₃O₄@MoS₂nanocomposites were prepared by hydrothermal method,and were characterized by various testing methods.The results showed that the Fe₃O₄@MoS₂nanocomposites have good magnetically controlled properties and a typical core-shell structure:Fe₃O₄nanospheres as the core and MoS₂nanosheets growing upright on the surface of Fe₃O₄nanospheres as the shell.Ultilizing the magnetic interaction between magnetic glassy carbon electrode and Fe₃O₄@MoS₂nanocomposite,the nanocomposite can be modified on the electrode surface without any adhesives to avoid the common problems of dissolution and desorption of nanomaterials.Further,the apt is adsorbed on the MoS₂nanosheet surface by using theπ-πinteraction between the MoS₂nanosheet and the apt.When the target is present,the apt-AFB1 complex is formed and comes off from the MoS₂surface by the specific binding between the target and the apt.Based on this detection principle,a label-free electrochemical aptasensor was constructed for the sensitive detection of aflatoxin B1（AFB1）with a linear range of 10 pg m L^-1-1000 ng m L^-1and a LOD of 3.4 pg m L^-1（S/N=3）.The aptasensor exhibited good selectivity and stability,and was successfully applied to the analytical detection of AFB1 in peanut samples.Compared with the large loss of specific surface area caused by the stacking of ordinary MoS₂nanosheets on the electrode surface,Fe₃O₄@MoS₂nanocomposites can make full use of the structural characteristics,which can provide more loading sites for biomolecules and provide a new idea for the development of high-performance label-free electrochemical sensors.2.Nitrogen-doped graphene quantum dots（NGQDs）emitting blue fluorescence were prepared by hydrothermal method,and NGQDs-labeled aptamer fluorescent bioprobe（NGQDs-apt）was prepared by coupling NGQDs with apt.Using this fluorescent bioprobe as the energy donor and Fe₃O₄@MoS₂as the energy acceptor,apt is adsorbed on the surface of MoS₂nanosheets through theπ-πinteraction,and when the distance between NGQDs and MoS₂nanosheets is close enough（<10 nm）,it leads to the occurrence of fluorescence resonance energy transfer（FRET）phenomenon,then the fluorescence of NGQDs-apt is burst by the MoS₂nanosheets.When the target AFB1 is present,based on the specific recognition between AFB1 and apt,NGQDs-apt forms a complex with AFB1and thus sheds from the surface of MoS₂nanosheets,resulting in the recovery of NGQDs fluorescence.Since the MoS₂nanosheets can not completely burst fluorescence signal of the fluorescent probe,causing interference and generating high blank background signal,the puzzle can take advantage of the magnetically controlled property of Fe₃O₄@MoS₂,which effectively reduces the background signal.The fluorescent aptasensor can achieve sensitive detection of AFB1 with a linear range of 1 pg m L^-1-10 ng m L^-1and LOD as low as 0.32 pg m L^-1（S/N=3）.This aptasensor has good selectivity and stability,which can providing a new idea for the construction of an easy-to-use and highly sensitive fluorescent aptasensor.3.Mercaptopropionic acid（MPA）-protected CdTeZn quantum dots（QDs）emitting red fluorescence were prepared by hydrothermal method,NGQDs（QDs1）and Cd Zn Te QDs（QDs2）were used as fluorescent probes,the two fluorescent bioprobes QDs1-apt1and QDs2-apt2 were coupled with their specific aptamers for deoxynivalenol（DON）and zearalenone（ZEN）,respectively.MoS₂nanosheets on the surface of Fe₃O₄as energy acceptors,and adsorbed QDs1-apt1 and QDs2-apt2 fluorescent bioprobes throughπ-πinteractions between MoS₂nanosheets and apt1（apt2）,leading to NGQDs and Cd Zn Te QDs bursted,and in the presence of the targets DON and ZEN,based on the specific binding interaction between apt1（apt2）and their respective targets,the QDs1-apt1（QDs2-apt2）were detached from the MoS₂surface,leading to the fluorescence recovery of QDs1（QDs2）to different degrees.The interference of the blank background signal was effectively reduced by exploiting the magneto-control property of Fe₃O₄@MoS₂nanocomposites.Based on this principle,a magnetically controlled fluorescent aptasensor was constructed,and the simultaneous detection of two mycotoxins,DON and ZEN,was successfully achieved.The linear detection ranges were 0.01-10 ng m L^-1and 0.01-50 ng m L^-1for DON and ZEN,respectively,and the LOD were 2.3 pg m L^-1and 3.7 pg m L^-1（S/N=3）,respectively.The sensor has good selectivity,reproducibility and stability,providing a new perspective for the simultaneous detection of two-component mycotoxins.