Dna Electrochemical Sensor Based On Nano-polyaniline

In this dissertation,the preparation of the modified electrodes by two kinds of conductive polyaniline(PANI) nanomaterials as well as the application in the DNA electrochemical biosensor have been investigated.The main contents and results are discussed as follows:(1) Polyaniline nano fibers doped with triethanolamine(TEA-PANI) have been deposited onto the Au electrode by the use of cyclic voltammetry(CV).The ssDNA probes are immobilized on the surface of TEA-PANI nano fibers through electrostatic adsorption.The morphology of the electrodes modified with TEA-PANI is examined using SEM and AFM. The electrochemical properties of the modified electrodes with or without TEA have also been studied by means of differential pulse voltammetry(DPV),square wave voltammetry (SWV) and CV.The results show that the conductivity of PANI doped with TEA has been enhanced greatly.The large specific surface areas of TEA-PANI nano fibers and rich positive ions benefit for the immobilization of DNA probe(negatively charged) through electrostatic adsorption.The hybridization signals are monitored using DPV and electrochemical impedance spectroscopy(EIS) techniques with the help of promethazine hydrochloride(PZH) as a hybridization indicator.The approach described here has been utilized successfully for the discrimination and detection of the complementary DNA.The mechanism of the detection system is also been investigated.The sensitivity of the fabricated sensor can be remarkably improved in the presence of TEA doping in the PANI nano fibers.(2) The modified electrode(PANI/BF₄/H₂SO₄) by the conductive PANI co-doped with ionic liquid[bmim]-BF4 and H₂SO₄ has been prepared.The influences of polymerization method,polymerization time,the doped ions and pH value on the electrochemical properties of the modified electrode are studied systematically.The morphology and chemical structure are characterized by AFM,UV and IR.The conditions of PANI polymerization has been optimized as follows:potentiostatic method(0.8V),polymerization time ofl50s.The optimal pH of PBS buffer is 6.1 for the best electrochemical performance of the PANI modified electrode when PZH is used as an indicator.The kinetic process of PZH on the PANI/BF₄/7H₂SO₄ modified electrode is also explored.The results from IR and UV indicate that ionic liquids have doped into PANI,which leads to the great enhancement of the PANI conductivity.(3) On the basis of the previous results,a highly sensitive DNA electrochemical biosensor has been developed,and the immobilization of DNA probes is improved due to the synergestic effect with the combination of nano-PANI,H₂SO₄ and ionic liquid[bmim]-BF₄. We also studied the interaction mechanism between the DNA and the indicator,PZH.The results reveal that two different behaviors of electrostatic and intercalation interactions have been found between PZH and ssDNA or PZH and dsDNA,respectively.The electrochemical process of PZH on the ssDNA or dsDNA modified electrodes is controlled not only by the diffusion,but also by the adsorption.The DNA electrochemical biosensors show the higher selectivity,lower detection line,which can be achieved for the quantitative detection of DNA hybridization.