Study On Electrochemical Sensing Of Biphenyl Organic Pollutants Based On DNA-Dye/CTS Membrane

Biphenyl organic pollutants are not easy to degrade and remain for a long time in the environment,which are harmful to human health.Biphenyl organic pollutants have no electrochemical activity,so it is difficult to realize direct electrochemical detection.In this paper,the double-stranded DNA was used as a recognition element,and electroactive dye molecules were used as redox indicators.The DNA-dye/chitosan（CTS）polyion complex membrane based on the intercalation between base pairs in the DNA double helix and small dye molecules was immobilized on the electrode surface.Electrochemical DNA sensor based on a DNA-dye/CTS modified electrode,was constructed for the electrochemical detection of trace biphenyl organic pollutants,and the amplifications of nanomaterials and enzyme for electrochemical detection signals were investigated.Firstly,the DNA/CTS polyion complex membrane was used to immobilize a DNA-dye modified electrode.Scanning electron microscopy,cyclic voltammetry and electrochemical impedance method were used to investigate the modified electrodes of DNA binding with three dye molecules[toluidine blue（TB）,methylene blue（MB）,and prussian blue（PB）].The results showed that the three polyion complex membranes were successfully immobilized on the electrode surface and exhibited a good stability.Cyclic voltammetry and differential pulse voltammetry were used to investigate the electrochemical response of 0～2.5μM monochlorobiphenyl on three kinds of modified electrodes.The results showed that the presence of monochlorobiphenyl inhibited the redox current of the modified electrodes and reduced the redox current.Secondly,an electrochemical sensor for detecting biphenyl organic pollutants was developed.Using the DNA-TB/CTS modified electrode as a template,the effects of various factors such as oxygen,reaction time,DNA type,and membrane component concentration on the response of monochlorobiphenyl on the modified electrode were investigated.The results show that in the presence of oxygen,with the reaction time of40 s,the concentration of TB of 0.4m M,CTS of 1mg/m L and DNA of 1mg/m L,the sensor exhibited a linear range of 0.5～5μM,a response sensitivity of 0.5182μA/μM,and the detection limit of up to 0.05μM（S/N=3）.In addition,the modified electrode had good selectivity,stability and reproducibility to the biphenyls response,and had potential application in the real samples.Finally,based on the DNA-TB/CTS modified electrode,four nanomaterials（high-density carbon nanotube KF,low-density carbon nanotube KC,graphene and Fe₃O₄magnetic nanoparticles）were added to construct the DNA-dye/nanomaterial/CTS polyion complex membrane modified electrode,which were used to study the signal amplification effect of modified electrodes to detect monochlorobiphenyl.The results showed that the addition of nanomaterials can significantly increase the base current of the modified electrode and improve the detection sensitivity.Under the optimum conditions,the detection sensitivity for 0.5～2.5μM monochlorobiphenyl was0.2578μA/μM.Compared with DNA-TB/CTS electrode,the sensitivity was increased by about 2.5 times,the detection limit was reduced to 0.01μM（S/N=3）,and it had strong anti-interference ability to glucose,Na Cl,ascorbic acid and other substances.The amplification effect of adding biological enzyme was also studied.Based on the horseradish peroxidase（HRP）catalyzed H₂O₂oxidation reaction,the DNA-dye/HRP/CTS modified electrode exhibited a detection sensitivity of 0.2128μA/μM and a detection limit of 0.01μM to monochlorobiphenyl response.