22 西南大学学报(自然科学版) 第30卷 Based Carbon nanotubes have attracted considerable attention since they were discovered in 1991 on the special characteristics and structure,carbon nanotubes were used widely in electron c aPPncat Ons・ Genera11v,carb叽nanotubes consist of two kinds:single—wall carbon nanotubes(SWNTs)and multi-waLl carbon nanotubes(MWNTs).In our study,we use the MWNTs for forming films to investigate the elec- trical properties.The electronic behaviors of MWNTs show that when used as an electrode mater al theY can be applied to improve the electron transfer reactions[1o_ z。. In the past MWNTs electrodes haVe been used for oxidation of DAClS], electrochemistry of protein ’ electrocatalysis oxygen ’ norepmeph— rineE1C,estradial[17],NO—D83,and cysteine[19]. The insolubilitv of MWNTs in most solvents is a central handicap for the preparation of MWNTs elec— trodes. In order to overcome this limitation,MWNTs were dealt with acidL2。]to bring hydrophilic groups at the sidewall and the terminus,and to shorten them into small segment.So far,MWNTs have been sue— cessfully dispersed in many solvents,such as concentrated sulfuric acid ,acetone ,poly(stYrene sulfo- nic acid)sodium salt(PSS)c23 l,dimethylformamide(DMF)[24],dihexadecyl phosphate(DHP) allyldimethy1ammonium chloride)c。 ,and nafion[ to obtain the modified electrode・ In our work,MWNTs were dispersed in SDS,obtaining a MWNTs—SDS modified glassy carbon elec— trode. Through the hydrophobic group between the sidewall of MWNTs and the hydrophobic chain of SDS causes a negative surface charge in order to improve the stability of MWNTs—SDS dispersionLz ・The re— ,poly(di— suIts of this experiment show that the modified electrode has obvious sensitive and excellent selectw e to- wards detecting DA in the presence of high concentration AA. 1 Experiment 1.1 Reagents and Material MWNTs were Durchased from Chengdu Institute of Organic Chemistry of China,and purified in nitric early,this treatment shortens nanotubes and causes carboxylation on the oPen acid solution for 10 hEZ0]Cl.ends of the nanotubes.DA,AA and sodium dodecyl sulfate(SDS)were purchased from Chongqing Chemi— ca1 Reagent Company,China.A buffer solution was 0.1 mol/L phosphate buffer solutions(PBS)contai— ning 0.1 mo1/L KC1,which were prepared with K H2 PO4 and Naz HPO4.Other chemicals used were of an— alytical grade.Twice distilled water was used during this study. 1.2 Apparatus Cyclic voltammetry(CV)measurements and differential pulse voltammetry(DPV)experiments were carried 0ut on a CHI-660A electrochemistry workstation from Shanghai Chenhua Apparatus Company・ A three-electrode system was used,containing a MWNT-SDS modified electrode as working electrode,a sat— urated calomel electrode(SCE)and a platinum wire as reference electrode and counter electrode,respec— tively.All experiments were carried out at room temperature・ 1.3 Electrode Preparation Before preparation of the modified electrode,the bare GC electrodes surface were polished with 0・3 “m and 0.05“m alumina slurry and then sonicated in double distilled water and ethanol and double dis— tn1ed water for 10 min,respectively.5.0 mg MWNTs were dispersed in SDS solution(0.025 g SDS'5 mL H2 O)to obtain a black dispersion.Then 10弘L of such dispersion was dropped onto the surface of a clean GC electrode via solvent evaporation to obtain MWNTs—SDS modified electrode. 2 Results and Discussion Behaviors of DA on the MWNT-SDS Modified Electrode ectrochemical 2.1 Elcyclic voltammograms of MWNT-SDS modified electrode in the absence of DA(curve Fig.1 shows the 维普资讯 http://www.cqvip.com 第1期XU Yang}et al:SelectiveDetection 0tD0pamineinthePresence 0fHigh-Concentrati0nAscorbicAcidUsnigMulti-wallCarbonNan0tubes-S0diumDodecylMiateM ̄ifiedGlassyCarbonElectric 23 a)and in the different concentration of DA(curve b—d)in 0.1 mol/L PBS(pH一6.0).Adding DA,a pair of the a— 60 nodic peak current and the cathodic peak current was clearly observed and increased with the concentration of DA in— 3O creasing.which indicating the MWNT—SDS modified elec— 0 trode has remarkable sensitive to determine DA. 2.2 Effect of Scan Rate on the MWN1 SDS Modified Elee— trode _o.2 O.O O.2 O.4 0.6 Fig.2(a)shows the cyclic voltammograms of the U MWNTs—SDS modified electrode in 0.1 tool/L(pH一6.0) a.0 mmol/L;b.0.10 mmol/L; PBS containing 0.10 retool/L DA at various scan rates. c.0.50 mmol/L;d.1.0 mmol/L. With the increasing scan rate,the anodic and cathodic peak Fig.1 Cyclic Voltammograms of the MWNTs-SDS currents increased and the peak potentials almost kept con— Modified Electrode in Different COncentratiOn of DA in stant.It was observe that the anodic and cathodic peak cur一 0.1 mol/L PBS(pH:6.0)at Scan Rate 50 mV/s rents altered linearly with the scan rate over the range of 1 0。——2 80 mV/s with the correlation coefficients of 0.993 3 and 0.997 3(Fig.2(b)),respectively,suggesting that the modified electrode surface is controlled by the adsorption of DA. 80 60 40 2O \ k 三 O 0 _2O 一40 —_o.2 O.O 0.2 O.4 0.6 60 O 5O 1O0 15O 2OO 25O 300 U~ v/(mY・s-1) (a) (b) Fig.2 a.Cyclic Voltammograms of the MWNTs-SDS Modified Electrode in 0.1 mol/L PBS(pH 6.0) Containing 0.10 mmol/L DA at Scan Rate of(from Inner to Outer):10。30。50。80。100。120。140。 160,180。200。220,250。and 280 mY/s;b.Plot of Peak Current Versus Scan Vate 2.3 Effect of pH on the MWNT-SDS Modified Electrode The influence of the solution pH value on the modified electrode was investigated and the cyclic volta— mmograms in PBS containing 0.10 mmol/L DA at various pH range from 4.0 to 9.0 are shown in Fig.3 (a).Both the anodic and cathodic peak potentials shifted negatively with an increase of pH value,and the anodic Deak current increaseed with the pH values before it reaches 6.0(Fig.3(b)).So pH 6.0 PBS was selected in this study. The connection between the forma1 potential(E ̄ )of DA which is obtained from the average of the a— nodic and cathodic peak potentials and the pH value was linear with the correlation coefficient of 0.987 6. The slope of一0.052 1 V/pH(Fig.4)indicated that the transfer process of electron is accompanied by an equal number of proton. 2.4 Determination of DA on the MWNT-SDS Modified Electrode Fig.5 shows the differential pulse voltammograms(DPV)on the modified electrode with the various concen— tration of DA in the present of 1.6 mmol/L AA.It revealed that the peak current of AA almost kept constant at 维普资讯 http://www.cqvip.com 24 西南大学学报(自然科学版) >\ 第30卷 surface can remark the different concentration of DA.Because the electronegative group of the modified electrode DA and AA on the ably distinguish the positive DA from the negative AA.Thus,electrochemical detections to modified electrode were obviously detected when they coexist in pH 6.0 PBS. 盘 盘 \ \ UN (a) Fig.3 a.Cyclic Vottammog rams of the MWNTs-SDS Modified Electrode in 0.1 mot/L PBS Containing 0.10 mM DA in pH of:4.0。4.5,5.0,5.5,6.0。6.5。7.0,7.5,8.0,8.5, and 9.0。at Scan Rate 50 mY/s;b.Plot of the Anodic Peak Cu rrent Versus pH 《 U CDA/(/ ̄mol・L一 ):a.0;b.0.10;c.0.2O;d・0・40;e.0・60; f.1.60;g.2.60;h.4.60;i.6.60;j.12.6;k.18.6;1.28.6; 133..38.6;n.58.6;at scan rate:5O 1TIV/S. Fig.4 The Formal Potential(Eo)Versus pH Fig.5 Differential Pulse VOIlammOg rams of the MWNTs-SDS Modified Electrode for AA(1.6 mmot/L)in the Present of Dif— ferenl COncenlraliOn of DA As it shown in the Fig.6,the peak current was 1inear with the various concentration of DA in the range of from 4.0×10 to 3.8×10 mol/L and from 9.8×10一 to 7.3×10一 mol/L.The linear regres— sion equation was ip ( A)一108.3+3.845c( ̄mol/L)and ip (tLA)一316.2+0.099 9c(/lmol/L)with the correlation coefficients of 0.992 4 and 0.959 8,respectively.The detection 1imit was 2.0×10一 mol/L. 2.5 The ReprOducibility and Stability of the MWNTs-SDS Modified Electrode The cyclic voltammograms of the MWNT—SDS modified electrode at the 0.1 mmol/I DA nearly re— mained constant with a relative standard deviation(RSD)of 3.1 (n一9),revealing the modified electrode possessed a good reproduvibi1ity.The stability of the modified electrode also was investigated.The elec— trode only decreased 7.9%after 1 00 continuous cyclic scanning.In addition,the modified electrode was stored in a refrigerator when not in use,the response decreased about 8.2 week the current decreased 1 5 . in one week and in the next 维普资讯 http://www.cqvip.com
第1期 xU Yang,et al:Selective Detection of D0pamine in the Presence of High-C0ncentrati0n Asc0rbie Acid Using Multi-wall Carbon Nan0tubes-S0dium D0deeyl Sulfate Modified Glassy aCrobn Electrode 2 5 ∞∞ ∞∞∞加 ∞ —5 0 5 10 15 2O 25 3O 35 40 c/( ̄mo1.L ) Fig 6 Calibration Plot for the MWNTs—SDS Modified Electrode n 0 1 rnol/L PBS+1.6 mmol/L AA and Various DA Concentration 3 Conclusion In this work,we demonstrated that the MWNT—SDS modified electrode exhibited remarkable sensitive to determine DA.At the same time,the proposed electrode also can be applied to the detection DA in the presence of high concentration AA. References: Eli Wightman R M,May L J,Michael A C.Detection of Dopamine Dynamics in the Brain EJ].Ana1 Chem,1988:769A 779A. E2] Salem F B.Spectrophotometric and Titrimetric Determination of Catecholamines EJ].Talanta,19'87:810—812. 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[27]Jiang L Q,Gao L,Sun J.Production of Aqueous Colloidal Dispersions of Carbon Nanotubes[J].Colloid and Interface Science,2003:89—94. 多壁碳纳米管一十二烷基磺酸钠化学修饰电极 在高浓度抗坏血酸体系中选择性测定多巴胺 许 阳, 袁 若, 陈时洪, 柴雅琴, 殷 冰 西南大学化学化工学院,重庆400715;重庆市现代分析重点实验室,重庆400715 摘要:研究了多巴胺(DA)在多壁碳纳米管一十二烷基磺酸钠(MWNTs-SDS)化学修饰电极上的伏安行为和在高浓度抗坏血 酸(AA)体系中对多巴胺的选择性.将多壁碳纳米管一十二烷基磺酸钠(MWNTs—SDS)分散液滴加到处理过的电极表面制备 生物传感器,以循环伏安法和示差脉冲伏安法研究多巴胺在MWNTs—SDS修饰电极上的电化学行为及其选择性.MWNTs— SDS修饰电极对多巴胺有显著的催化作用,在pH为6.0的磷酸盐缓冲溶液中,氧化峰电流值与多巴胺的浓度在4.0X10—7 ~3.8X10 mol/L和9.8X10 ~7.3 X10 mol/L成线性关系,检测限为2.0X10- mol/L,MWNTs—SDS修饰电极具有 响应快、灵敏度高、稳定性好、线性范围宽的性能,能在高浓度抗坏血酸体系中选择性测定多巴胺. 关键词:多壁碳纳米管;十二烷基磺酸钠;多巴胺;抗坏血酸;化学修饰电极 责任编辑潘春燕
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