Study Of The Interaction Of Pyrethroid Insecticides With DNA And Their Electrochemical Biosensor

Since DNA electrochemical biosensors was describe by Millan and Mikkelsen for the first time, they have received widespread attention.They are a new type of biosensors developed in recent years.DNA electrochemical sensors are mostly used to detect the target sequence (or specific gene), while the detection of pesticides of small molecules have less relevant reports.With the continual emergence of various pesticides,pesticide residues have become a serious problem of the world, and thus the studies of new detection methods have also become the focus of attention. Electrochemical biosensors have a lot of characteristics, such as high sensitivity, low cost, easy operation, and good compatibly with other equipments.Pyrethroids become a breakthrough following the organochlorine pesticides, organophosphorus pesticides, and carbamate pesticides.Pyrethroids synthesized by the chemical structure of nature pyrethrins are used very popular and efficient, while they harm to the nerve. At present, the detection methods of synthetic pyrethroid insecticides are mostly concentrated on the chromatography and immunoassay, while few applications of electrochemical method have been reported.DNA is the material basis of gene expression, and study on the interaction of DNA with pyrethroid insecticides will help us to understand their mechanism from the molecular level and have an important significance guiding for us to research the DNA biosensor of pesticides.The immobilization of DNA is the key step for the DNA eletrochemical biosensor. On the one hand, the interaction between two different structure types of synthetic pyrethroid insecticides and DNA were studied by spectrometry, after that we can clear their interaction mode.On the other hand, based on the interaction mode, we prepared a DNA electrochemical biosensor for pyrethroids.The detailed matericals are shown as follows:(1)The interaction of allethrin and tetramethrin with single strand DNA (ssDNA), double strand DNA, guanine and guanosine were studied by UV and fluorescence spectrophotometry. Pyrethroid pesticides brought about a hypochromic effect on the UV absorption spectrum of DNA, but the maximum absorption wavelength of DNA did not shift obviously; the addition of different concentrations of DNA caused the fluorescence quenching of pesticides.It was investigated that the effect of ionic strength and KI on the system of pesticide-DNA respectively as well as the effect of pesticides on the neutral red-DNA.The results indicated that the electrostatic binding and groove binding are the two major modes of the interaction between allethrin and DNA, while electrostatic binding mainly exists between tetramethrin and DNA. The UV and fluorescence spectra proved that the interaction of the pesticides on guanine and guanosine were hydrogen bonds chiefly, and the pesticides have s stronger interaction with guanosine than that with guanine.(2) The interaction of cypermethrin and fenvalerate with DNA were studied by UV and fluorescence spectrum.The UV absorption spectrum of DNA was increasing after adding pyrethroid pesticides into the solution;a fluorescence quenching effect of pesticides and the quenching process was proved to be the single static.Effect of ionic strength and I- concentration on interaction between pesticide and DNA as well as that of pesticide on interaction of neutral red and DNA were investigated.The results indicated that the intercalation binding is the major mode of the interaction of cypermethrin and fenvalerate with DNA.Guanine and guanosine interact with pesticides mainly by hydrogen bonds,and guanosine interact with pesticides stronger than guanine.(3)A DNA biosensor was fabricated by electrochemical deposition of nanogold on overoxidized polypyrrole(Ppyox)film, formed a DNA/nano-Au/Ppyox composite on glassy carbon electrode and carbon fiber electrode. The electrochemical behaviors of Cypermethrin and Fenvalerate were studied at DNA/nano-Au/Ppyox modified glass carbon electrode by using cyclic vohammetry(CV),chronoamperometry(CA)and chronocoulometry(CC).The kinetic parameters such as charge transfer coefficient a, diffusion coefficient D and electrode reaction rate constant k were determined. The result indicated that the differential pulse voltammetric (DPV) peaks at DNA/nano-Au/ Ppyox modified glass carbon electrode of Cypermethrin and Fenvalerate were at-0.76 and -0.75 V, respectively. The liner response was obtained in the range of 5.8×10-8 to 1.3×10-6 mol/L with a detection limit of 1.0×10-8 mol/L for Cypermethrin,and in the range of 9.5×10-8 to 5.7×10-6 mol/L with a detection limit of 3.0×10-8 mol/L for Fenvalerate. On the modified carbon fiber electrode also have a good detection range and detection limit.