Simultaneous determination of catechol and hydroquinone by carbon paste electrode modified

JSolidStateElectrochem(2012)16:3747–3752DOI10.1007/s10008-012-1813-5

ORIGINALPAPER

DirectelectrochemistryofglucoseoxidaseimmobilizedonTiO2–graphene/nickeloxidenanocompositefilmanditsapplication

Chun-XuanXu&Ke-JingHuang&Xue-MinChen&Xiao-QinXiong

Received:2April2012/Revised:23June2012/Accepted:2July2012/Publishedonline:13July2012#Springer-Verlag2012

AbstractAnovelelectrochemicalplatformbasedonnickeloxide(NiO)nanoparticlesandTiO2–graphene(TiO2–Gr)wasdevelopedforthedirectelectrochemistryofglucoseoxidase(GOD).Theelectrochemicalbehaviorofthesensorwasstudiedusingcyclicvoltammetryandchronoamperom-etry.Theexperimentalresultsdemonstratedthatthenano-compositewellretainedtheactivityofGODandthemodifiedelectrodeGOD/NiO/TiO2–Gr/GCEexhibitedex-cellentelectrocatalyticactivitytowardtheredoxofGODasevidencedbythesignificantenhancementofredoxpeakcurrentsincomparisonwithbareGCE.Thebiosensorrespondedlinearlytoglucoseintherangeof1.0–12.0mM,withasensitivityof4.129μAmM 1andadetectionlimitof1.2×10 6Munderoptimizedconditions.Theresponsetimeofthebiosensorwas3s.Inaddition,thedevelopedbiosensorpossessedgoodreproducibilityandstability,andtherewasnegligibleinterferencefromotherelectroactivecomponents.

KeywordsTiO2–graphene.Nickeloxidenanoparticles.Glucose.Glucoseoxidase.Biosensor

Introduction

Increasingattentionhasbeenfocusedonthestudyofthedirectelectrochemistryofproteinsbecauseofitssignifi-canceinbothprobingthenatureofenergyconversionprocessesinbiologicalsystemsanddevelopmentofthird-generationbiosensors[1,2].However,itisdifficultfor

C.-X.XuK.-J.Huang(*)X.-M.ChenX.-Q.XiongCollegeofChemistryandChemicalEngineering,XinyangNormalUniversity,Xinyang464000,China

e-mail:kejinghuang@

proteinstoexchangeelectronsdirectlywithbaresolidelec-trodesbecausetheelectroactivecenterofproteinsisdeeplyburied.Thedirectelectrontransferbetweenglucoseoxidase(GOD)andelectrodecannotbeachievedeasily.Nanomate-rialshavebeenwidelyusedforconstructionofbiosensorduetotheintrinsicadvantages,suchaslowcost,goodthermalstability,andlargesurfacearea.Especially,metalnanoparticlescanprovideasuitablemicroenvironmentforbiomoleculesimmobilizationretainingtheirbiologicalac-tivityand,tofacilitateelectrontransferbetweentheimmo-bilizedproteinsandelectrodesubstrates,haveledtoanintensiveuseofthosenanomaterialsfortheconstructionofelectrochemicalbiosensorswithenhancedanalyticalperfor-mancewithrespecttootherbiosensordesigns.Duetotheiruniquechemicalandphysicalproperties,manykindsofmetalnanoparticles,suchasgoldnanoparticles,platinumnanoparticles,andAgnanoparticles,havebeenusedinthefabricationofbiosensorsforglucoseanalysis[3–7].

Nickeloxide(NiO)nanoparticleshavereceivedconsid-erableattentioninrecentyearsduetotheircatalytic,optical,electronic,andmagneticproperties[8,9].Theeasyprepa-ration,electroinactivityinphysiologicalpHsolutions,andhighporosityareadvantagesofNiOnanomaterialsfortheentrapmentofelectrontransfermediators.TheycanbeusedfortheimmobilizationofdifferentmoleculesbasedontheuniquepropertiesofNiOnanoparticles.Forexample,theuseofNiOnanoparticlesfortheimmobilizationofbiomo-leculesandtheirapplicationsforhydrogenperoxideandglucosedetectionhasbeenreported[10,11].

Graphene(Gr)isamonolayeroftightlypackedcarbonatoms.Itissuitedforelectrochemicalapplicationsduetoitshighelectricalconductivity,largesurfacearea,uniquehet-erogeneouselectrontransferrate,andlowproductioncosts.Recently,Grhasbeenwidelyutilizedinchemical,electron-ic,information,energy,materials,biologicalmedicine,andotherfields[12,13].However,manyoftheinterestingand

3748uniquepropertiesofGrcanonlyberealizedafteritisintegratedintomorecomplexassemblies.SomeGr-basedhybridmaterialshaveshowngreaterversatilityasadvancedelectrodematerialsforthefabricationofelectrochemicalsensorsandbiosensors[13,14].TiO2isametaloxideandhasbeenwidelyusedinthefabricationofelectrochemicalsensorsandbiosensorsduetoitsgoodbiocompatibilityandhighconductivity[15,16].Mostrecently,wereportedtheTiO2–graphene(TiO2–Gr)nanocompositeusedinelectro-chemicalbiosensorconstructionandtheirapplicationinsomebiomoleculesensing,suchasdopamine,glucose,ad-enine,andguanine[17–19].TiO2–Gr-basedanalyticalmethodsshowedexcellentperformance,suchashighselec-tivity,broaddynamicrange,andlowdetectionlimit,whichowedtothecharacteristicsandadvantagesofTiO2–Grnanocomposite,anditopenedanewplatformforelectro-chemicalsensorsandbiosensorsdesign.

Herein,weemployedtheTiO2–GrandNiOcompositesasapropellantofdirectelectrontransferbetweenGODandtheelectrodesurface.Amediator-freeGOD-basedglucosebiosensorwasconstructedthoughalayer-by-layerassemblyapproach.Firstly,theNafion-stabilizedTiO2–GrcompositeswerecoatedonthesurfaceofGCE.Then,NiOwaselectro-depositedontheresultingelectrode.Finally,GODwasself-assembledonthelargeandspecificsurfaceofTiO2–Gr/NiO.Thebiosensorexhibitedspecificandsensitivedetec-tionforglucosewithshortresponsetime,lowdetectionlimit,andhighsensitivity.Preparation,characterization,performance,andfactorsinfluencingtheperformanceoftheobtainedbiosensorwereinvestigated.

ExperimentalMaterials

Graphitepowder,hydrazinesolution(50wt.%),andam-moniasolution(28wt.%)wereobtainedfromShanghaiChemicalReagentCorporation(Shanghai,China).GODwasobtainedfromSigma(SaintLouis,MO,USA).Ti-taniumisopropoxide(Ti(OiPr)4,98%)wasobtainedfromAladdinChemistryCo.,Ltd.Phosphate-bufferedsolutions(PBS)werepreparedbymixingthesolutionsofKH2PO4,Na2HPO4,andKCl.Double-distilledwaterwasusedthroughout.Instruments

CHI660Delectrochemicalworkstation(CHInstruments,Shanghai,China)andastandardthree-electrodecellwhichcontainedaplatinumwireauxiliaryelectrode,asaturatedcalomelreferenceelectrode(SCE),andthemodifiedelectrodeasworkingelectrodewereemployedforelectrochemical

JSolidStateElectrochem(2012)16:3747–3752

studies.AllofthepotentialsinthisarticlewerewithrespecttoSCE.ThepHmeasurementsweremadewithapHmeter(MP230,Mettler-Toledo,Greiffensee,Switzerland).PowderX-raydiffraction(XRD)datawerecollectedonaRigakuMiniFlexIIX-raydiffractometer.Scanningelectronmicros-copy(SEM)imageswereobtainedonaHitachiS-4800scan-ningelectronmicroscope.

PreparationofTiO2–Grnanocomposite

Grapheneoxide(GO)waspreparedfromgraphitepowderbythemodifiedHummersmethod[20].Graphitewasputintoamixtureof12mLconcentratedH2SO4,2.5gK2S2O8,and2.5gP2O5.Thesolutionwasheatedto80°Cwithcontinuousstirringfor5husingoilbath.Next,themixturewasdilutedwithdeionizedwater(500mL).Theproductwasobtainedbyfilteringusing0.2-μmNylonfilmanddriednaturally.Theproductwasre-oxidizedbyHummersandOffemanmethodtoproducethegraphiteoxide.Exfoliationwascarriedoutbysonicating0.1mgmL 1graphiteoxidedispersionfor1h.TiO2–Grnanocompositewaspreparedaccordingtothepreviouswork[17].Inshort,20mgofGOwasdispersedinamixedsolutionofH2O(10mL)andethanol(5mL)underultrasonicationfor1htogetaho-mogenouscolloidalsuspensionofexfoliatedGO.Then,0.2mLofTi(OiPr)4wasaddedtotheGOsuspensionandultrasonicatedforanother1h.Theresultantmixturewastransferredtoa25-mLTeflon-sealedautoclaveandkeptat130°Cfor12h.Thefinalproductwasisolatedbyfiltrationandrinsedthoroughlywithwaterandethanol,respectively.Then,theproductwasdriedinvacuum.TheTiO2–Grnano-compositewasobtainedintheformofblackpowder.Fabricationofmodifiedelectrode

Atotalof1.0mgoftheas-preparedTiO2–Grnanocompo-sitewasdispersedin10.0mL0.25-wt.%Nafionsolutionsunderultrasonicationfor30mintoobtainahomogeneous,well-distributedsuspensionofNafion-TiO2–Grcomposite.Priortothemodification,thebareGCE(3mmindiameter)wascarefullypolishedtoobtainamirror-likesurfacewith0.3and0.05μmaluminaslurry,followedbysuccessivesonicationinwaterandethanolfor5minanddryinginair.Subsequently,20μLofpreparedNafion-TiO2–GrwasdroppedonthecleanedGCEanddriedunderaninfraredlamptopreparetheTiO2–Gr/GCE-modifiedelectrode.Modificationoftheelectrodewasaccomplishedbytrans-ferring10μLof2mMnickelnitratesolutiontothesurfaceofTiO2–Gr/GCEanddryingunderaninfraredlamp.Theelectrodewasthenconditionedbypotentialcyclinginalimitedrange(0.1–0.6V)in0.10MNaOHsolution,assupportingelectrolyte,untilasteadystatevoltammogramwasobtained.ThemodifiedelectrodeNiO/TiO2–Gr/GCE

JSolidStateElectrochem(2012)16:3747–37523749

wasobtained.Atotalof5μLGODsolution(10mgmL 1)wasthencoatedontheNiO/TiO2–Gr/GCE(GOD/NiO/TiO2–Gr/GCE)anddriedat4°C.ThemodifiedGCEwasimmersedinPBStoremovethelooselyabsorbedGODandwasstoredat4°Cinarefrigeratorwhennotinuse.

thanthatofTiO2,whichresultsintheshieldingofthegraphenepeaksbythoseofTiO2[21].

Electrochemicalbehaviorsofmodifiedelectrodes

Theelectrochemicalbehaviorsofdifferentmodifiedelectro-deswereinvestigated.TheresultsshowedthatanodicandcathodicpeaksdonotappearatGCE,TiO2–Gr/GCE,NiO/GCE,andNiO/TiO2–Gr/GCEin0.1MPBS(pH7.0).AftercombiningwithGOD,apairofwell-defined,quasireversi-bleredoxpeakscanbeobservedatGOD/NiO/TiO2–Gr/GCEat 0.46and 0.41V,withapeak-to-peakseparationofabout50mV,revealingafastelectrontransferontheelectrode.

Figure2showsthecyclicvoltammetricresponsesobtainedatGOD/GCE,GOD/NiO/GCE,GOD/TiO2–Gr/GCE,andGOD/NiO/TiO2–Gr/GCE,respectively.Apairofbadlydefined,weakredoxpeakscanbeobservedatGOD/GCE.TheredoxpeaksobservedatGOD/NiO/GCEandGOD/TiO2–Gr/GCEobviouslyincreasedwhencom-paredtothatatGOD/GCE,revealingafastelectrontransferatbothmodifiedelectrodes.ThepeakcurrentofredoxpeaksofGOD/NiO/TiO2–Gr/GCEwasthehighestintheaformen-tionedelectrodes,whichwasduetothesynergisticeffectofNiOandTiO2–Gr.

ResultsanddiscussionCharacteristics

TheSEMimageofGr(Fig.1a)revealsthetypicalcrumpledandwrinkledGrsheetstructure.TheintegrationbetweenTiO2andGrcanbevisualizedinFig.1b,inwhichTiO2nanoparticleswithsizeofca.20–30nmareuniformlyandcompactlyembeddedontheGrsubstrate.Figure1cshowsthatNiOnanoparticlesareelectrodepositedonTiO2–Gr.TheXRDpatternsofTiO2–GraregiveninFig.1d.ThepeaksinthisdiffractionpatternscorrespondtotheanatasephaseofTiO2(JCPDSfileno.21–1272),suggestingthecompleteformationofanataseTiO2duringthehydrother-malprocess.However,thediffractionpeaksofGrarenotdistinguishableinXRDpatternsofTiO2–Gr.Thisphenom-enahasalsobeenobservedinotherrelevantworks,anditcanbeascribedtothemuchlowercrystallineextentofGr

Fig.1SEMimagesofGR(a),TiO2–Gr(b),andNiO/TiO2–Gr(c);XRDpatternsofTiO2–Gr(d)

cd

Intensity / a.u.

2500200015001000

004

200105211

204

101

20

40

60

80

2θ/ degree

116220215

500

3750

20

10

A

0μ / I-10-20

-30

E / V

Fig.2CVsofGOD/GCE(a),GOD/NiO/GCE(b),GOD/TiOGr/GCE(d)in0.1MPBS(pH7.0)

2–Gr/GCE(c),andGOD/NiO/TiO2–Electrochemicalimpedancespectroscopy(EIS)wasreportedasaneffectivemethodtomonitorthefeatureofsurface,allowingtheunderstandingofchemicaltransformationandprocessesassociatedwiththecon-ductiveelectrodesurface.Figure3showstheNyquistplotsofEISforthebareGCE,TiO2–Gr/GCE,NiO/GCE,NiO/TiO2–Gr/GCE,andGOD/NiO/TiO2–Gr/GCE.AtbareGCE,theredoxprocessofthe[Fe(CN)6]3 /4 probeshowedaveryweakelectrontransferresistance(curvea).TheEISincreasedwhenTiO2–Grwasmod-ifiedontheGCE(curveb).TheEISofNiO/GECobviouslyincreasedcomparedtobothoftheaforemen-tionedelectrodes(curvec).TheNiO/TiO2–Gr-modifiedGCEshowedamuchlowerresistancefortheredoxprobe(curved),implyingthatNiO/TiO2–Grwasanexcellentelectricconductingmaterialandacceleratedtheelectrontransfer.AfterGODwascoatedonNiO/TiO2–Gr/GCE,theresistanceincreaseddramatically

Ω

/ ''ZZ' / Ω

Fig.3EISspectraofbareGCE(a),TiO2–Gr/GCE(b),NiO/GCE(c),NiO/TiO2–Gr/GCE(d),andGOD/NiO/TiO2–Gr/GCE(e)in5mMFe(CN)63 /4 solutioncontaining0.1MKCl

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(curvee),suggestingthatthebulkyGODmoleculesblockedtheelectronexchangebetweentheredoxprobeandelectrodesurface.Differentscanratestudies

ThecyclicvoltammogramsofGOD/NiO/TiO2–Gr/GCEinPBSatdifferentscanrateswerestudied.BothIpaandIpcincreasedlinearlywithincreaseinscanratesfrom20to300mVs 1.ThisindicatedthattheelectrontransferprocessoccurringatGOD/NiO/TiO2–Gr/GCEwasasurface-confinedprocess.EffectofpH

TheeffectofpHonGODredoxcoupleatNiO/TiO2–Gr/GCEinvariousbuffersolutions(pH5.0to10.0)wasinves-tigated.TheredoxpeakcurrentincreasedwithincreaseofpHfrom5to6andthenremainedalmoststableinthepHrangeof6to8.ThepeakcurrentdecreasedwhenpHincreasedfrom8to10.So,pH7.0wasselectedastheoptimum.TheinfluenceofpHovertheanodicpeakpoten-tial(Epa)andcathodicpeakpotential(Epc)atNiO/TiO2–Gr/GCEwasstudiedanditshowedthatbothEpaandEpcexhibitedlineardependenceoverdifferentpHs.Thecorre-lationcoefficientwas0.998and0.995,respectively.TheslopevaluesofEpaandEpcwerefoundtobe 50.3and 50.5mVpH 1,respectively.Theslopeswereclosetothetheoreticalvalueof 58.6mVpH 1forareversiblereaction,whichindicatedanequalnumberofprotonandelectrontransferprocesses.

Amperometricresponseoftheglucosebiosensor

Theamperometriccurrent–timecurveofGOD/NiO/TiO2–Gr/GCEuponsuccessiveadditionofglucosetoacontinu-ouslystirredPBS(pH7.0)wasrecorded(Fig.4).Thebiosensorexhibitedarapidresponsefortheadditionofglucoseandachieved96%ofthesteady-statecurrentwithin3s.TheinsetofFig.4picturedthecalibrationcurveofGOD/NiO/TiO2–Gr/GCEforglucosedeterminationanditsequationwasI(μA)02.503+4.129Cglucose(mM)withacorrelationcoefficientof0.995.Agoodlinearrelationshipwasfoundbetweenthechronoamperometriccurrentandglucoseconcentrationfrom1to12mM.Meanwhile,thedetectionlimitof1.2μMwasestimatedatasignal-to-noiseratioof3.ThesensitivityofGOD/NiO/TiO2–Gr/GCEbio-sensor(4.129μAmM 1)wassuperiorthanreportedforbiosensorsofglucose,1suchasGOD/Chit-MWCNTs(0.45μAmM )[22],GrEC/Chit-CNT/GOD(1.38μAmM 1)[23],CS/glutaraldehyde/GOD(1.8μAmM 1)[24],andGOD/Au/CS-IL/MWNT(4.10μAmM 1)[25].ThehighsensitivityforGOD/NiO/

JSolidStateElectrochem(2012)16:3747–37527060

50

A

40μ/ I3020100

Time / s

Fig.4TheamperometricresponseofGOD/NiO/TiO 0.3Vuponsuccessiveadditionsofglucose(1mM)2in–Gr/GCE0.1MpHat7.0PBS.Inset,plotofamperometriccurrentvs.glucoseconcentration

TiO2–Gr/GCEwasexpectedtooriginatepresentinfromthematrix.

thecombinedinfluenceofTiO2–GrandNiOAplateauincurrentresponsewasobservedforaglucoseconcentrationbeyond12mM.ThissignifiedtheoperationoftheMichaelis–Mentenkineticmechanismfortheenzyme-catalyzedprocess.TheapparentMichaelis–Mentenconstant(KM),aparameterofimportanceinenzyme–sub-stratekinetics,wasobtainedfromtheLineweaver–Burkequation[26]:1/Iss01/Imax+KM/ImaxC,whereIssisthesteady-statecurrentaftertheadditionofsubstrate,Cisthebulkconcentrationofsubstrate,andImaxisthemaximumcurrentmeasuredundersaturatedsubstratesolution.Analysisoftheslopeandinterceptfortheplotofthereciprocalofthesteady-statecurrentversusreciprocalofglucoseconcentra-tionallowsthedeterminationofKM.TheKMvaluefortheenzymeelectrodewasfoundtobe7.3mM.ThevalueofKMforGODatGOD/NiO/TiO2–Gr/GCEwaslowerincompar-isontootherglucosebiosensorsbasedonGOD-immobilizedPMMA-MWCNT(PDDA)-NFE(KM010.12mM)[27]andPrussianblue/MWCNTnanocomposites(KM018mM)[28].ThelowerKMvalueshowsabetteraffinitybetweenglucoseandenzymeelectrode.

Stability,repeatability,andinterferencedeterminationThestabilityoftheproposedbiosensorwasinvestigated.Whennotinuse,theelectrodewassuspendedabove0.1MPBSat4°C.Theresponseofthebiosensorto1.0mMglucosewastestedintermittently.Thebiosensorlostabout5.2%and10.3%ofitsoriginalresponseafter10and20days,respectively.Thebiosensoralsoshowedgoodreproducibilityforthedeterminationofglucoseconcentra-tioninitslinearrange.Therelativestandarddeviation(RSD)was1.9%forsixsuccessiveassaysataglucose

3751

concentrationof1.0mM.ThiscanbeduetothegoodbiocompatibilityofNiO/TiO2–Grcomposite,whichpro-videsafavorablemicroenvironmentforGOD.

Theabilityofthesensortodiscriminatetheinterfer-ingspecieshavingelectroactivitiessimilartothetargetanalyteisoneofthemostimportantanalyticalfactorsforanamperometricbiosensor.Easilyoxidizablecom-poundssuchasascorbicacid,dopamine,anduricacidnormallyco-existwithglucoseinnaturalsamples.Theinterferenceeffectof5.0mMl-cysteine,5.0mMglycin,2.0mMascorbicacid,2.0mMuricacid,and2.0mMdopamineontheamperometricresponseof1.0mMglucosewasinvestigated.Thecurrentresponseforsuchelectroactive-interferingspeciestothatofglucosebythesensorwasbelow5%.Therefore,goodselectivitycanbeobtainedwiththepreparedsensor.Samplesanalysis

Inanattempttoexplorethedevelopedsensorforpracticalapplications,GOD/NiO/TiO2–Gr/GCEwasappliedtodeter-mineglucoseinhumanbloodserumsamplesofhealthypeople.Arapidandstableamperometricresponsewasac-quiredat 0.3Vwiththedirect 1additionof20μLofsamplesinto20mLof0.1molLPBS.ThecontentofglucoseinthesampleswascalculatedfromthecalibrationcurveandtheobtainedresultsareshowninTable1.TherecoveryofglucosewasdeterminedbystandardadditionofpureglucosetothesolutionscontainingtheserumsamplesandthecorrespondingresultsaregiveninTable1.Onecanseethatthesensoralsogivesexactrecovery(96.3–103.4%).TheresultsdemonstratedhererevealthepotentialapplicationsofGOD/NiO/TiO2–Gr/GCEfordeterminationofglucoseinbiologicalfluids.

Conclusions

Theconstructionofanelectrochemicalbiosensorbymodi-ficationofaglassycarbonelectrodewithafilmcontainingTiO2–GrandNiOwasreported.TheGOD/NiO/TiO2–Gr/GCEbiosensorwaspreparedtodetectglucoseusingNiO/

Table1Determinationofglucoseinhumanserumsamples(n04)SampleConcentration(nM)

RSD(%)Added(nM)Recovery(%)

13.451.5598.222.682.5596.334.561.95102.544.283.45103.45

2.15

4.1

5

97.6

3752TiO2–GrnanocompositetoimmobilizeGODasamodelenzyme.TheevaluationofGOD/NiO/TiO2–Grnanocomposite–Gr/GCEhadadem-onstratedthatNiO/TiO2goodabilitytoretainthebioactivityofGOD.Cyclicvoltammetryshowedapairofwell-definedredoxpeaks,correspondingtothedirectelectrontransferofGOD.ThepresenceoftheredoxpeaksindicatedthattheNiO/TiO2–GrnanocompositefacilitatedthedirectelectrontransferofGOD.Themethodpresentedcanbeusedfortheimmobilizationandevaluationofthedirectelectrontransferofotherenzymesorproteins.

AcknowledgmentsThisworkwassupportedbytheNationalNatu-ralScienceFoundationofChina(20805040),ProgramforScienceandTechnologyInnovationTalentsinUniversitiesofHenanProvince(2010HASTIT025),andExcellentYouthFoundationofHe’nanScientificCommittee(104100510020).

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