Based On Multi-walled Carbon Nanotube / Polymer Composite Film Modified Electrode Determination Of Dopamine, Ascorbic Acid And Uric Acid

Dopamine.uric acid and ascorbric acid alx~ays co-exist in biological samples, Low lexrel of dopamine may cause neurological disorder,such as schizophrenia and Parkinson's disease;The inconsistency of uric acid in human body can induce many diseases.such as gout,hyperuricaemia and Lesch-Nyan diseases The ascorbric acid. as antioxidant.can be used for the prevention and treatment of common cold,mental illness,infertility.cancer and AIDS.Therefore.it is of clinical significance to develop simple and effective methods for measm'ing dopamine,uric acid and ascorbric acid to prevent these diseases.Among the various methods for detecting them.electrochcmical determination of them has demonstrated to be a preferred method due to its simplicity,,fast response,and high sensitivity However.the co—existence of ascorbric acid and uric acid in biological samples makes it difficult for the selective detection or simultaneous detection them.And,these compounds have nearly the same oxidation potentials at common electrodes and often suffer fl'om a pronounced fouling effect,kx,hich results in rather poor selectivity and reproducibility,Recently.multiwalled carbon nanotubes and poly mer modified electrode received great attention duo to their individual perproties.But the multiwalled carbon nanotubes is insoluble and can't exist long on the surface of electrode.Though the polymer is stable on the surface of electrode,but the catalytic isn't enough to selective detection or sinmltaneous detection bioactive molecule,such as.dopamine.uric acid and ascorbric acidIn ordre to utilize the good properties of nmltiwalled carbon nanotubes and polymer,the multiwalled carbon nanotubes was frist purified with hydrochloric acid and then acidified with nitric acid and obtained the MWNT functionalized with carboxylic acid functionalities.Then electrochemical polymerization of polymer at the surface of multiwalled carbon nanotubes modified electrode.Based on the different electrochemical behaviors of AA.DA and UA at the PABS-MWNT composite film modified GCE.the simultaneous determination of DA and UA in the presence ofAA at PABS—MWNT/GCE has been studied. The paper includes four sections as followed:1.A multiwalled carbon nanotubes(MWNT)modified glassy carbneton electrode(GCE)coated with poly(orthanilic acid)(PABS)film(PABS-MWNT/GCE) has been fabricated and used for simultaneous determination of dopamine(DA)and uric acid(UAl in the presence of ascorbic acid(AA)by differential pulse voltammetry(DPV).Scanning electron microscopy(SEM),Fourier transform infrared (FT-IR)spectra and electrochemical techniques have been used to characterize the surface morphology of the composite film and the polymerization of ABS on electrode surface.In comparison with the bare GCE and the MWNT modified GCE, the PABS—MWNT composite film modified GCE,which combines the advantages of MWNT and the self-doped PABS,exhibits good selectivity and sensitivity for the simultaneous and selective determination of UA and DA in the presence of AA.Due to the different electrochemical responses of AA,DA and UA,the PABS.MWNT/GCE can resolve the overlapped oxidation peak of DA and UA into two well-defined voltammetric peaks with greatly enhanced current responses using both cyclic voltammetry(cv)and DPV.The peak potential separations between DA and UA are 170 mV using CV and 1 60 mV using DPV,respectively,which are large enough for the selective and simultaneous determination of these species.In the presence of O.5 mM AA.the DPV peak currents are linearly dependent on the concentration of UA and DA in the range of 6~55μM and 9~48μM with correlation coefficients of 0.997 and 0.993,respectively The detective limits(3)for detecting UA and DA are 0.44 pM and O.21 p.M.respectively.The PABS—MWNT/GCE shows good reproducibility and stability,and has been used for the simultaneous determination of DA and UA in the presence of AA in samples with satisfactory results.2.Three—dimension(3D)belt—like polyaniline(PAN)network has been prepared via electrochemical polymerization of aniline on P-phenylenediamine(PDA) functionalized glassy carbon electrode(GCE)using a three-step electrochemical deposition procedure.PDA was covalently binded on GCE via the formation of carbon-nitrogen bond between anline cation radical and the aromatic moiety of GCE surface using electrochmnical oxidation procedure.X—ray photo—electron spectroscopy(XPS)and cyclic voltammetry have been performed to characterize the attachment of PDA Oll GCE.The images of scanning electron microscope(SEM) show that the 3D belt—like PAN network iS uniform The width and thickness of the PAN belt varies in the range of 1.5～5.5 gm and O.1～O.8 um.respectively.The distance between the belt—contacts ranges from 2.5 tO 1 5 gm The 3D belt—like PAN network modified GCE fPAN—PDA/GCE) exhibits an improved electro-activity of PAN at an extended pH up to 7.0.The PAN-PDA/GCE not only immobilizes but also leads tO a direct electrochemical behavior of cytochrome C(Cyt c).The immobilized Cyt C maintains its activity,showing a surface—controlled electrode process with the electron transfer rate constant(ks)of 1 4 . 8 S-1 and electron transfer coefficient(a)of 0.48,and could be used for the electrocatalytic reduction of hydrogen peroxide(H202).3.Poly(alizarin red S)(PARS)and multiwalled carbon nanotubes(MWNT) composite film have been synthetized 011 the glassy carbon electrode(GCE)and applied to simultaneous determination of dopamine(DA)and uric acid(UA)by differential pulse voltammetry(DPV)in comparison with the bare GCE and the MWNT modified GCE,the PARS—MWNT composite fihn modified GCE.exhibits good selectivity and sensitivity for the determination of UA and DA by reducing the over-potential about 97 mV for DA and 56 mV for UA with enhanced current responses using cyclic voltammetry(cv).and strongly excludes the oxidation of AA by suppressing the anodic peaks ofAA tO some extent.The peak potential separations between DA and UA are 1 50 mV using CV and 1 40 mV using DPV,respectively. which are large enough for the selective and simultaneous determination of these species.In the presence of O.5 mM AA,the DPV peak currents are linearly dependent onthe concentration ofUA andDAinthe range of0～11 5 gM and 5.4～55 gMwith correlation coefficients of 0.998 and O.997,respectively.The detection limits (S/N=3)for detecting UA and DA are 4.1 6 laM and 1 66μM.respectively.The PARS—MWNT/GCE shows good reproducibility and stability,and has been used for the simultaneous determination of DA and UA in the presence of AA in samples with satisfactory results.