Investigated Of The Interaction Of DNA Bases With Pesticide And The Application Of Aptamer Sensor By Surface-enhanced Raman Scattering

This work mainly focuses on the study of DNA bases SERS spectra,interaction mechanism of bases and pesticides,and the detection method of pesticide marathon using aptamer.Nucleic acid bases are the main components of DNA,which is closely linked to biological growth,development,reproduction and other abnormal life activities,such as mutations,cancer.Therefore,the nature of the base has been one of the important research contents in the field of biology and chemistry.The study of the interaction between DNA bases and pesticides can be detailed from the molecular level,which is of significance to understand the mechanism of toxic-making,carcinogenic production and gene mutations.It can also provide the basis to construct and filter out the aptamer for pesticide.Therefore,using aptamer combined with SERS method of Malathion is a practically meaningful work.Firstly,nano-Ag particles and nano-Au particles with high SERS activity were synthesized by chemical reduction method;the nanoparticles morphology was dominated by spherical and elliptical shapes.Then the SERS spectra of adenine,guanine,thymine and cytosine on nano-Ag substrate were recorded and illustrated combing with quantum chemistry density functional theory(DFT).The theoretical Raman spectrum was compared with the normal Raman spectra(NRS)and SERS,and their peaks were analyzed and assigned.Furthermore,the influence of silver metal clusters on the spectrum of adenine was studied theoretically.The results showed that the simulation spectrum and the actual SERS can be better matched,the distance between N of Adenine and Ag decreases and the static polarization rate increases with the increase of the number of Ag atoms,which is related to the peak intensity of simulated Raman spectrum.All above shows that charge transfers existes between the N of the adenine ring with the silver.Secondly,the adsorption characteristics and regularity of cytosine(Cy)on the silver substrate surface were analyzed by SERS combing with DFT.The SERS spectra of Cy molecules on nano-Ag were recorded at different adsorption time,concentration and pH.The results show that the pH value had the greatest impact on its SERS signal.It was inferred that there are two different isomers of Cy molecules and three kinds of existing forms,and all of them keep dynamic balance in the solution.The adsorption mechanism of Cy on the surface of silver substrate was further discussed in detail based on the morphological distribution of Cy at different pHs by their corresponding SERS changes combining with the DFT calculation of charge distribution in Cy molecules.In conclusion,the N3 and O in Cy are coordinated to Ag at the neutral and weakly alkaline conditions.N and Ag form coordinated adsorption and O and Ag form covalent adsorption,when the pH is higher than 11.Based on the above research,the interactions of Fenthion with four kinds of DNA bases in solution were investigated by UV and SERS.The results demonstrate that the amino-containing three bases(adenine,guanine,and cytosine)the amino groups of these three bases are the main binding sites?,while thymine ring was the binding site?.The DFT calculation is shown that Fenthion and bases binding at a different site has different impact on the bases ring breath vibration of the bases,that is the closer the binding site to the base ring,the greater the effect on ring breathe vibration peak.Finally,we develop a SERS method for the specific detection of Malathion using silver sol and aptamer.The SERS spectra of the aptamer-Malathion target and four organophosphorus pesticides were characterized.The results showed that the aptamer-Malathion target has characteristic peaks of 1089 and 1112 cm-1.And the intensity of 1112 cm-1 has a good linear wtith the concentration in the range of 5�10-7~1�10-5 mol�L-1.Also,the feasibility and specificity of this method were verified by the simulation samples.Therefore,the proposed method could specifically detect Malathion in the coexistence of a variety of pesticides and shows the advantages of operation easy and good specificity.