Investigation Of Signal-enhanced Photoelectrochemical DNA Sensors For Mycotoxins And Organophosphorus Pesticide Residues

Mycotoxins and pesticide residues are harmful to human health and cause environmental pollution.Therefore,reliable and sensitive quantitative analysis and detection of mycotoxins and pesticide residues are essential in food safety.Photoelectrochemical?PEC?DNA bioanalysis technology,combined DNA bioanalysis with photoelectrochemical sensing,possessed the advantages of good specificity,high sensitivity,simple operation,and so on.Signal amplification is important to the performance of the PEC sensor.Thus,this research focuses on the investigated signal amplified PEC DNA sensor for sensitive detection of organophosphorus pesticide.The major contents are summarized as follows:1.The work reports a novel and efficient method for converting the photo-responsive of the DNA strand and the validation of its feasibility for using as a versatile signal amplified system for constructing PEC DNA sensor.Emeraldine polyaniline molecule could grow and enwrap the long linear DNA polymeric skeleton with the catalytic ability of embedded fenton reagent and DNAzyme.Indeed,the DNA backbone converted to the photoactive matrix that can efficiently enhance the utilization of visible light,thus improve the photocurrent response in essence.Inspired by this phenomenon,employing the long linear DNA polymeric skeleton which generated by target-triggered hybrid chain reaction as the template for loading ferrous ions and DNAzyme,an distinctive PEC platform was proposed based on decahedral Au-BiVO₄@MoS₂ as the photoactive substance.The generated PANI wire can efficient adsorption of light in the visible region and produced more electrons,thus further restrain the electron-hole recombination of Au-BiVO₄@MoS₂,endowing the DNA sensor with excellent analytical performance.Under optimal conditions,the proposed PEC assay shows excellent sensitivity for detection of ochratoxin A with a low detection limit of 0.14 pg mL^-1 and wide linear range from 0.25 pg mL^-1 to 25 ng mL^-1.Moreover,it presents good stability,satisfactory accuracy,and is a promising methodology for determination of multiple other targets by replacing the recognition elements.2.A PEC aptasensing platform was designed for the screening of malathion based on the in situ propagation of Bi₂S₃ on the flower-like BiOBr,relying on the product H₂S from Na₂S₂O₃ reduction reaction in the presence of H₂O₂.The flower-like BiOBr with eminent PEC performances was conveniently synthesized and utilized to provide an initial photocurrent response.With the target malathion,the bioconjugate of dsDNA/MB were disintegrated,resulting in the release of biotin-DNA/MB.The released biotin-DNA/MB was able to hybridize with H₁ and H₂to perform a hybridization chain reaction?HCR?and finally form a long G-rich dsDNA,which was employed as a skeleton to combine hemin as DNAzyme and insert abundant MnTMPyP.Upon addition of Na₂S₂O₃ and H₂O₂,appropriate amount of H₂S was generated with use of DNAzyme and MnTMPyP as catalyst.Thereafter,the generated H₂S could react efficiently with BiOBr to form BiOBr/Bi₂S₃ complexes,thereby generating an elevated photocurrent.Under optimum conditions,the designed PEC aptasensor displayed a wide detection range from 0.001 to 1000 ng mL^-11 with a detection limit of 0.12 pg mL^-1 for malathion,which demonstrated outstanding PEC properties of the BiOBr/Bi₂S₃ complexes and enormous potential of its“green”synthesis procedures for PEC analysis.3.A sensitive PEC aptasensor has been constructed for malathion detection based on in situ enzymatic catalytic generation of silver nanoparticles.First,the g-C₃N₄/AgCl nanomaterials was synthesized and modified on ITO electrode as PEC electrode.In the presence of the target malathion,the malathion aptamer was released from the magenetic probe?aptamer/biotin-DNA/MB?.The biotin-DNA/MB can hybrid with auxiliary chain-Au-ALP.The ALP on the probe can catalyze the deposition of silver nanoparticlesto form“Z-scheme”g-C₃N₄/AgCl@Ag nanocomposites.Under the optimal experimental conditions,the aptasensor shows high sensitive for malathion with,the LOD of 0.25 pg mL^-1.