Research On Fluorescence Aptasensor For Detection Of Mycotoxins In Maize And Barley

Cereals are susceptible to fungal infection during the growth,reposition,and transport,causing decay and deterioration,which easily produces mycotoxins that are toxic secondary metabolite with carcinogenicity,teratogenicity and mutagenicity under appropriate environmental.Nowadays,analytical methods for the detection of mycotoxins based on chromatographic mass spectrometry and immunoassay are accurate and reliable,but they frequently rely on expensive equipment and professional operation.Therefore,many efforts have been made to establish novel detection methods for simple,accurate,and sensitive analysis of mycotoxins.In this paper,from the perspective of developing high-sensitivity and high-specificity method for mycotoxins detection in maize and barley,new sensing platform was designed for two mycotoxins,ochratoxin A（OTA）and zearalenone（ZEN）,using fluorescent aptamer sensing technology and carbon-based quantum dots as fluorescent probes.The work includes the following two parts:（1）For the first time,CoOOH nanosheets were used as quencher of carbon nitride quantum dots（g-CNQDs）.Based on the diversity of Van der Waals’force between CoOOH nanosheets and aptamers with different configurations,a simple and sensitive“Turn-on”fluorescent aptasensor for the detection of OTA in maize and barley was successfully constructed.Due to the fluorescence resonance energy transfer（FRET）between g-CNQDs and CoOOH nanosheets,the fluorescence signal of g-CNQDs could be quenched by 90%.In the presence of OTA,the linear aptamer specifically bound with OTA to form G-quadruplex,which had weak adsorption capacity on the surface of CoOOH nanosheets,causing the FRET was hindered and the fluorescence of g-CNQDs was restored.Thus,OTA concentration-dependent recovery of the fluorescence was realized.The linear response range of the“Turn-on”aptasensor ranged from 1.00 nmol L^-1 to 140 nmol L^-1,and the limit of detection（LOD）was 0.50 nmol L^-1.The fluorescence aptasensor had been successfully applied to detect OTA in maize and barley flour with the recoveries between 94.5%and101%.（2）In order to overcome the shortcoming that the single fluorescence signal is easily affected by the external factors including environmental,probe concentration etc.,and further improve the reliability and sensitivity of the sensing method,a accurate,sensitive and selective ratiometric fluorescence aptasensor for ZEN detection was designed on basis of the quenching effect of mitoxantrone（MTX）on silica sphere-encapsulated cadmium telluride quantum dots（CdTe@SiO₂）.Nitrogen-doped graphene quantum dots（NGQDs）and CdTe@SiO₂ were selected as reference and response probes,respectively.The fluorescence of CdTe@SiO₂ could be quenched by MTX through the internal filtration effect（IFE）due to the spectral overlap between MTX and CdTe@SiO₂,but the fluorescence of NGQDs remaind unchanged.The linear response of the ratiometric fluorescence aptasensor to ZEN concentration changed from 1.00 pmol L^-1 to 1.00 nmol L^-1,and the LOD was 0.33pmol L^-1.The ratiometric aptasensor had been successfully applied to detect ZEN in maize and barley flour,and the addition standard recoveries were between 97.8%and110%.The detection results were basically consistent with the results of the high performance liquid chromatography-fluorence method（HPLC-FL）,indicating good accuracy of the developed aptasensor.