Research On Detection Of Typical Mycotoxins In Agricultural Products Based On Magnetically Controlled Aptasensor

Mycotoxins brought about not only huge economic losses but also harms for human beings. Nowadays, conventional detection technologies for mycotoxins in agricultural products could not meet the needs of the market which has become urgent problem to be solved because of low sensitivity, consuming time, bad reproducibility. In this paper, novel aptasensors combining with fluorescence, colorimetry, and electrochemiluminescence were developed using magnetic substance as carrier and different nano-materials as signals. The aptasensors were used for sensitive detection of ochratoxin A(OTA) and fumonisin B1(FB1) in agricultural products. Improving a rapid, online detection technology for mycotoxins in agricultural products become an urgent task.This paper was mainly focused on:1. Magnetic gold(Au) nanoparticles(NPs) doped Fe3O4(Au@Fe3O4) hybrid NPs have been synthesized by the facile one-step solvothermal method for the first time. Compared with the priste Fe3O4 NPs obtained by the same conditions, Au@Fe3O4 NPs were found to possess a smaller size, loose structure, and a higher peroxidase-like activity. In addition, an efficient colorimetric aptasensor has been developed using the intrinsic dual functionality of the Au@Fe3O4 NPs as signal indicator and magnetic separator. Initially, the amino-modified aptamer specific for a typical mycotoxin, OTA, was surface confined on the amino-terminated glass beads surafce using glutaraldehyde as a linker. Susequently, the amino-modified capture DNA(c DNA) was labeled with the amino-functionalized Au@Fe3O4 NPs and the sensing interface was thus fabricated through the hybridization reaction between c DNA and the surface confined aptamers. While upon OTA addition, aptamer prefer to form the OTA-aptamer complex and the Au@Fe3O4 NPs linked on the c DNA were released into the bulk solution. Through a simple magnetic separation, the collected Au@Fe3O4 NPs can produce a blue colored solution in the presence of 3,3’,5,5’-tetramethylbenzidine and H2O2. When the reaction was terminated by addition of H+ ions, the blue product could be changed into a yellow one with a higher intensity. By employing this trategy, an efficient colorimetric aptasensor has been developed for OTA detection in a wide linear range from 0.5 to 100 ng m L-1 with a detection limit of 0.03 ng m L-1.2. A facile method was proposed to prepare the nitrogen-doped graphene quantum dots(NGQDs) doped silica(NGQDs@Si O2 NPs) for the first time. The NGQDs@Si O2 NPs were further explored as versatile signal indicator for OTA aptasensing by combination with electrochemiluminescence(ECL) and fluorescence(FL) detection. In this strategy, the core-shell Fe3O4@Au magnetic beads(MBs) acted as a nanocarrier to immobilize the thiolated aptamer specific for OTA and the amino-modified capture DNA(c DNA) was efficiently tagged with NGQDs@Si O2 NPs. The multifunctional aptasensor was thus fabricated by assembly of the NGQDs@Si O2 NPs onto the surface of Fe3O4@Au MBs through the high specific DNA hybridization. Upon OTA incubation, the aptamer linked with Fe3O4@Au MBs preferred to form aptamer-OTA complex, which resulted in the partial release of the preloaded NGQDs@Si O2 NPs. The more OTA molecules in the detection system, the more NGQDs@Si O2 NPs were released into the bulk solution and the less preloaded NGQDs@Si O2 NPs were accumulated on the magnetic electrode surface. This provided a dual channel for OTA detection by combination with the enriched solid-state ECL and homogeneous FL detection. The as-prepared aptasensor showed excellent performance for OTA detection with a linear range of 1 pg m L-1 to 10 ng m L-1 and detection limit of 0.5 pg m L-1(S/N = 3) with ECL and a linear range of 10 pg m L-1 to 100 ng m L-1 and detection limit of 3 pg m L-1(S/N = 3) with FL.3. A multifunctional aptasensor for highly sensitive and one-step rapid detection of OTA, has been developed using aptamer-conjugated magnetic bead(MBs) as the recognition and concentration element with a heavy Cd Te quantum dots(QDs) as the label. Initially, the thiolated aptamer was conjugated on the Fe3O4@Au MBs through Au-S covalent binding. Subsequently, multiple Cd Te QDs were loaded both in and on a versatile Si O2 nanocarrier(Cd Te@Si O2@Cd Te) to produce a large amplification factor of hybrid fluorescent nanoparticles(HFNPs) labelled complementary DNA(c DNA). The magnetic-fluorescent-targeting multifunctional aptasensor was thus fabricated by immobilizing the HFNPs onto MBs’ surface through the hybrid reaction between the aptamer and c DNA. This aptasensor can be produced at large scale in a single run, and then can be conveniently used for rapid detection of OTA through a one-step incubation procedure. The presence of OTA would trigger aptamer-OTA binding, resulting in the partial release of the HFNPs into bulk solution. After a simple magnetic separation, the supernatant liquid of the above solution contained a great number of Cd Te QDs produced an intense fluorescence emission. Under the optimal conditions, the FL intensity of the released HFNPs was proportional to the concentration of OTA in a wide range of 15 pg m L-1~100 ng m L-1 with a detection limit of 5.4 pg m L-1(S/N=3).4. A magneto-controlled aptasensor has been developed for simultaneous electrochemical detection of ochratoxin A(OTA) and fumonisin B1(FB1), two typical mycotoxins found in food crops world-wide. This aptasensor was designed using the high specificity between the target and aptamer with heavy Cd Te or Pb S quantum dots coated silica as labels and the complementary DNA functionalized magnetic beads as capture probes. In presence of targets, the aptamer preferred to form the target-aptamer binding which forced the partial release of the preloaded labels from the magnetic beads. After a one-step incubation and a simple magnetic separation, the electrochemical signals of Cd2+ and Pb2+ dissolved from the reserved labels which had negative correlation with targets contents, was measured based on the difference of peak potentials. This aptasensor provided a wide detection range of 10 pg m L-1~10 ng m L-1 for OTA and 50 pg m L-1~50 ng m L-1 for FB1, and succeeded in real maize samples.The results implied that the aptasensors can be synthetically used to rapidly, sensitively, and simultaneously detect the mycotoxins in agricultural products, and provide reference for detection of other food. The using of aptamer can improve the efficiency and reduce the costs for detection of mycotoxins. The using of nano-materials can enhance the sensitivity for detection of mycotoxins owing to signal amplification, excellent photoelectric properties. Colorimetric determination can achieve semiquantitative determination by naked eyes for mycotoxins in agricultural products and have a extensive future for portability.