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SensorsandActuatorsB138(2009)182–188

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SensorsandActuatorsB:Chemical

journalhomepage:www.elsevier.com/locate/snb

Layer-by-layerassembledhybridﬁlmofcarbonnanotubes/ironoxidenanocrystalsforreagentlesselectrochemicaldetectionofH2O2

YuqingMiaoa,b,∗,HuaWangb,YuyanShaob,ZhiwenTangb,JunWangb,YueheLinb,∗∗

ZhejiangKeyLaboratoryforReactiveChemistryonSolidSurfaces,InstituteofPhysicalChemistry,ZhejiangNormalUniversity,Jinhua321004,ChinaPaciﬁcNorthwestNationalLaboratory,Richland,WA99352,USA

articleinfoabstract

AnewapproachtoconstructareagentlesselectrochemicalH2O2sensorisdescribed.Ironoxidemagneticnanocystals(IOMNs),asperoxidasemimetics,wereassembledtoformamultilayerstructurethroughthelayer-by-layer(LBL)method.Polythionin(PTh)wasﬁrstelectrodepositedontotheglassycarbonelectrode(GCE)surfacetointroduceaminogroups.Carboxylfunctionalizedmulti-walledcarbonnan-otubes(MWCNTs),aminofunctionalizedIOMNs,andthioninmonomerswerealternativelyanchoredontoapolythionin-functionalizedGCEsurfaceinorderbycarbodiimideorglutaraldehydechemistry.TheresultingmultilayerconstructionwiththreelayersofIOMNsandthioninmediatorexhibitsexcellentelectrochemicalresponsetothereductionofH2O2,whereassuchamodiﬁedelectrodewithonelayerconstructiononlyyieldsaslightresponsetoH2O2ofthesameconcentration.ThetetheredMWCNTsenlargetheamountofimmobilizedIOMNsandeffectivelyshuttleelectronsbetweentheelectrodeandthethionin.ThecalibrationplotislinearoverthewideH2O2concentrationrangefrom0.099to6.54mM,withadetectionlimitof53.6␮M.

Articlehistory:

Received27October2008

Receivedinrevisedform15December2008Accepted20December2008

Availableonline31December2008Keywords:

Carbonnanotube

MagneticnanocystalsPeroxidasemimeticsH2O2

1.Introduction

Duetotheirnanometer-scalesize,biocompatibilityandcapa-bilityofbeingmanipulatedunderanexternalmagneticﬁeld,ironoxidemagneticnanocystals(IOMNs)haveshownadiverserangeofapplicationsinbiomedicineareas[1–5].Magneticnanoparti-clesaregenerallyconsideredtobechemicallyandbiologicallyinert.Recently,YanandcoworkersmadethesurprisingdiscoverythatIOMNsexhibitanintrinsicenzymemimeticactivitysimilartonaturalperoxidases[6].Intheirstudy,IOMNsweredemon-stratedtobeahighlyeffectivecatalyst,andtheirbindingafﬁnityforthesubstrate3,3,5,5-tetramethylbenzidineismuchhigherthanthatofhorseradishperoxidase(HRP).Also,IOMNswerefoundtoremainstableoverawiderangeofpHandtemperatures.Morerecently,Wang’sgroupreportedthecolorimetricmethodfortheassayofH2O2byemployingIOMNstocatalyzetheoxidationof2,2-azino-bis(3-ethylbenzo-thiazoline-6-sulfonicacid)diammo-niumsaltintothecoloredproduct[7].Thedetectionforglucosewas

∗Correspondingauthorat:ZhejiangKeyLaboratoryforReactiveChemistryonSolidSurfaces,InstituteofPhysicalChemistry,ZhejiangNormalUniversity,Jinhua321004,China.Tel.:+8657982283109;fax:+8657982283109.∗∗Correspondingauthor.Tel.:+15093716241.

alsoveriﬁedbycombiningglucoseoxidasewithIOMNs.Thedetec-tionplatformsforH2O2andglucosefurtherconﬁrmedthatIOMNspossessintrinsicperoxidase-likeactivity,indicatinggreatpotentialapplicationsinvarioussimple,robust,andeasy-to-makeanalyticalapproachesinthefuture.

Variousdyemoleculeshavebeenusedaselectron-transfermediatorsinfabricatingofHRP-basedH2O2biosensors,amongwhichthioninmoleculesaregainingtheincreasinginterest.Thionin,asmallplanarmolecule,hastwo–NH2groupssymmetri-callydistributedoneachside,whichmakesitagoodcandidateforcovalentconjugationwithothermoleculesormaterials.ItiswellrecognizedthatthioninexhibitsexcellentelectrochemicalredoxpropertiestowardincreasedelectrocatalyticalactivityofenzymesinthereductionofH2O2[8–10].Inaddition,polythionin(PTh)couldbeelectrochemicallydepositedontovariouselectrodesurfacesandkeepsanexcellentefﬁciencyofelectrontransferbetweentheHRPandtheH2O2electrode[11,12].

Thelayer-by-layer(LBL)depositionmethodformultilayerﬁlmisoneofthetechniqueswidelyusedtofabricatefunctionalmaterialsonananoscale,becauseofitssimplicity,controllability,andver-satility.Inthiswork,multi-walledcarbonnanotubes(MWCNTs)weremodiﬁedontoPTh-electrodepositedglasscarbonelectrode(GCE),followedbythealternativeanchoringIOMNsandthionininLBLway,resultinginanewenzymeelectrodeforthereagentlesselectrochemicaldetectionofH2O2.

Y.Miaoetal./SensorsandActuatorsB138(2009)182–188183

Scheme1.Thestructureofthionin.

2.Experimental

2.1.Chemicalsandmaterials

Thioninacetate(Scheme1),1-(3-(dimethylamino)propyl)-3-ethylcarbodiimidehydrochloride(EDC),andN-hydroxysulfosuccinimide(NHS)werepurchasedfromSigma–Aldrich(Milwaukee,WI).MWCNTswithapurityof95%andahollowstructure(OD:15±5nm;ID7±2nm;length:1–5␮m)wereobtainedfromNanoLab(Brighton,MA).IOMNs(diameter20nm)terminatedwithcarboxylgroupsinwaterandthosewithaminegroupswerefromOceanNanoTech(Fayetteville,AR).pH7.4phosphatebuffersolution(PBS)waspreparedwith0.01Mphosphatebuffer,0.137MNaCl,and2.7mMKClunlessotherwisenoted.ThewaterusedthroughoutallexperimentswaspuriﬁedwithaMilli-Qsystem(Millipore,Bedford,MA).Allexperimentswerecarriedoutatroomtemperature.

MWCNTswithcarboxylicgroupsarelinkedwiththeaminogroupsofpolythioninusingwell-knowncarbodiimidechemistry,whichhasbeenreportedextremely[14,15].ToattachMWCNTsontothepolythioninmodiﬁedGCE,2␮lof1.4mg/mlMWCNTTwatersolutionwascastontheelectrodeanddriedinair.Then,2␮loffreshlyprepared0.2MEDCand0.1MNHSSinwaterweredroppedontotheMWCNT-coveredelectrode,washedoffafter0.5handdried.Thiswasimmediatelyfollowedby15minincubationwith2␮lof4mg/mlIOMNsinwaterwithanaminegroup,washedoffanddried.ThentheaminogroupsofIOMNswereactivatedby2␮lof2.5%glutaraldehydefor15min,washedthoroughlyanddried.Later,theelectrodewasincubatedfor15minwith2␮lofsaturatedthioninsolutioninwater.TheobtainedelectrodewascarefullywashedwithwatertoremovethephysicallyabsorbedchemicalsaftereachreactionstepandwereblownovertheﬁlmsurfacewithanN2streamuntiltheadheringwaterwascompletelyremoved.Themultilayerﬁlmsweredepositedbyalternatelycoveringtheelectrodesurfacewithglutaraldehyde,IOMNs,glutaraldehydeandthionininorder.RepetitionoftheaboveproceduresledtotheformationofalternatingIOMN/Thmultilayerﬁlmswithadesirednumberofbilayers{IOMN/Th}n.Themultilayerﬁlmswerereferredtoas{IOMN/Th}n(Scheme2).IOMNsmeanthosewithaminogroupsunlessotherwisenoted.

Forcomparison,IOMNswithcarboxylandthosewithaminegroupsweredepositedontothepolythionin-modiﬁedGCEwith-outMWCNTs.TheformerwasdonewiththehelpofEDCandNHSS,andthelatterwiththehelpofglutaraldehyde.Bothweremodiﬁedwithalayerofthioninbyglutaraldehydeagain.2.3.Apparatus

ElectrochemicalexperimentswereperformedwiththeCHI660electrochemicalworkstation.Aconventionalthree-electrodecellwasusedwithanAg/AgClasthereferenceelectrode,aPtwireasthecounterelectrodeandaGCEdisk(2mmdiameter,modiﬁedorunmodiﬁed)astheworkingelectrode.3.Resultsanddiscussion

Thioninisaphenothiazineredoxdyewithtwo–NH2groupssymmetricallydistributedoneachside.Boththioninmonomerandtheelectrogeneratedpolythioninhaveexcellentelectrocatalyticactivitytowardtheredoxofsmallmolecularcompounds.Here,

2.2.PreparationofIOMN-modiﬁedGCEwithLBLmethod

MWCNTswerecarboxyl-functionalizedandshortenedbysoni-cationin3:1HNO3/H2SO4for4hat70◦C[13].Thedispersionswereﬁltered,washedwithwater,driedanddispersedinwater.

TheGCEwasﬁrstcarefullypolishedwithaluminaonpolishingcloth.Theelectrodewasthenplacedinethanolandsubjectedtovibrationtoremoveadsorbedparticles.Finally,theelectrodewasrinsedwithdistilledwater.

TointroducetheNH2–functionalgroupontheGCEsurface,theelectrodewasﬁrstscannedwithcyclicvoltammogram(CV)of2.5cyclesbetween−0.4and1.2Vatascanrateof100mV/sin1:1HAcsolutioncontaining2␮Mthionin.Astableﬁlmofpolythioninwasdepositedontheelectrodesurface.

Scheme2.IllustrationsofGCE/PTh/MWCNT/{IOMN/Th}1assembledinLBLwayusingaminofunctionalizedIOMNsandthionin.

184Y.Miaoetal./SensorsandActuatorsB138(2009)182–188

Fig.1.CVsofablankGCE(a),GCE/PTh(b)andGCE/PTh/MWCNTT/{IOMN/Th}1(c)electrodeinpH7.4PBS,scanrate:100mV/s.

weattemptedelectropolymerizationofthionintofunctionalizetheGCEsurfaceforthecovalentimmobilizationofMWCNTs.

BasedontheCVsrecordedduringtheelectrochemicaldeposi-tionofpolythioninattheGCEinthioninsolution(notshown),theirreversibleanodicoxidation,whichcommencesatabout950mV,correspondstotheoxidationoftheNH2groupsofthethioninmolecule[16].ThereversibleredoxresponsewiththeE0ofabout−0.015V(thevaluesofEpc,Epa,and󰀁Epare−0.022,−0.006,0.018V,

Fig.3.CVsofGCE/PTh/MWCNT/{IOMN/Th}1electrodesinPBSwithdifferentpHs4.24(a),6.03(b),7.02(c),7.4(d)and8.05(e).

respectively)isduetotheredoxreactionofthioninmonomers.Dur-ingtheprocessofthioninelectropolymerization,thecurrentsofanotherpairofredoxpeaks,withacathodicpeakpotential(Epc)of0.112Vandananodicpeakpotential(Epa)of0.152V,increasedgraduallywithincreasingscannumber,whichmeanstheformationofelectrodepositedpolythionin.

Fig.2.(A)CVsofGCE/PTh/MWCNTT/{IOMN/Th}1electrodeinpH7.4PBSwithdifferentscanrates:40,60,80,100,200,400,600and800mV/s.The(B)and(C)showtherelationshipbetweenscanratesandredoxpeakpotentialsorcurrent.

Y.Miaoetal./SensorsandActuatorsB138(2009)182–188185

Fig.4.CVsofaGCE/PTh/{IOMN/Th}1withamino-functionalizedIOMNs(A),GCE/PTh/{IOMN/Th}1withcarboxyl-functionalizedIOMNs(B),GCE/PTh/MWCNT/{IOMN/Th}1withamino-functionalizedIOMNs(C),GCE/PTh/MWCNT/{IOMN/Th}2withamino-functionalizedIOMNs(D)andGCE/PTh/MWCNT/{IOMN/Th}3withamino-functionalizedIOMNs(E)electrodeinpH7.4PBSintheabsence(a)andpresence(b)of1mMH2O2;scanrate:100mV/s.

WhentheblankormodiﬁedelectrodeswerewashedandexaminedinpH7.4PBS,theCVsconﬁrmedthepresenceofsurface-attachedelectroactivematerial.AscanbeseenfromFig.1,theblankGCEdoesnotshowanyredoxresponse.TheGCE/PThexhibitstheredoxprocessofthioninmonomersandPTh,whichshowsthatPThhasbeensuccessfullydepositedontotheelec-trodesurfaceandpartofthioninmonomersalsoentrappedintothepolymermatrix.SuchaeventisfurtherconﬁrmedbytheCVofGCE/PTh/MWCNT/{IOMN/Th}1wheretheredoxresponseofthioninmonomerincreasesduetotheintroductionofmorethioninmonomersontotheelectrodesurfacebycovalentreac-tionofglutaraldehyde.ThisresultindicatesthatalargeamountofthioninmoleculeshavebeensuccessfullymodiﬁedontotheGCEsurface.Also,themultilayerstructurecaneffectivelyshuttleelec-tronsbetweentheelectrodeandthethionin.

Inordertoconﬁrmthatthecurrentresponseisasso-ciatedwithsurfaceconﬁnedthioninredox,thedependenceofthepeakcurrentsonscanrateswaschecked.CVsofGCE/PTh/MWCNT/{IOMN/Th}1electrodeinpH7.4PBSwithdiffer-entscanrateswerestudiedintherangeof40–800mV/s(Fig.2).Twopairsofdistinctredoxpeaksareobservedattheformalpotential(E0)ofca.−275.5mVand−99mV,withaverysmallpeak-to-peakofabout47mVand66mV.Also,thepeakpotentials,theformalpotentialsandtheseparationofthepeakpotentials(󰀁Ep)areinde-pendentofscanrates.Theeffectsofthepotentialscanrate(v)ontheoxidationpeakcurrent(Ipa1,Ipa2)andreductionpeakcurrent(Ipc1,Ipc2)havebeeninvestigated(datanotshown).Therelation-shipbetweenpeakcurrentsandthescanratesgivesthelinearresults.Alsotheredoxpeakcurrentsratioisunityatallscanrates.Allofthesedemonstratefacilechargetransferkineticsofsurfaceconﬁnedthioninorpolythioninoverthisrangeofsweeprates.

TheeffectsofpHontheGCE/PTh/MWCNT/{IOMN/Th}1elec-trodeswereinvestigatedbyrunningCVsusingPBSatvariouspHvaluesfrom4.24to8.05.AsshowninFig.3,theformalpotentials

186Y.Miaoetal./SensorsandActuatorsB138(2009)182–188

ofthesurfaceredoxcouplewerepHdependent.TheanodicandcathodicpeakpotentialsshiftlinearlytowardthenegativedirectionwithincreasingsolutionpH.AplotofE0vs.pHgivesastraightlinefrompH4.24to8.05withaslopeof38.3mV/pH.ThisphenomenonsuggeststhattheredoxprocessofThinvolvedtwoelectronsandoneproton[16].

ThedeterminationofH2O2isofpracticalimportanceinchemical,biologicalandmanyotherﬁelds[17,18].Thisapproachalsoholdsgreatpotentialapplicationsinvariousoxidase-basedbiosensors[19,20].TheCVsofthemodiﬁedelectrodestoH2O2werestudiedinFig.4.TheGCE/PTh/{IOMN/Th}1withamino-functionalizedIOMNs(A)andtheGCE/PTh/{IOMN/Th}1withcarboxyl-functionalizedIOMNs(B)giveaslightreductionresponseto1mMH2O2.Theresponsedifferencebetween(A)and(B)shouldbeduetothedifferentimmobilizationefﬁcienciesofIOMNwithdifferentfunctionalgroups.Thatis,thecatalyticabilityisduetoIOMNsotherthancarboxyloraminegroupderivertized.Moreover,itwasfoundthatuseofredoxthioninmayimprovetheelectrontransferfeatureoftheelectrode.However,TheCVresponsetoH2O2isstillsmallpresumablyduetothelowelectrocatalyticactivityofIOMNs.

ToenhancetheelectrocatalyticabilityofIOMNstoH2O2,MWCNTswereemployedtomodifytheGCEbeforeIOMNswereimmobilized.Here,IOMNswithaminogroupswerestudiedasamodelofmimicperoxidase.ThecatalyticreductioncurrentofH2O2wasgreatlyimproved,startingatabout0Vtoincreasewiththenegativeshiftofpotential.Obviously,thereductioncurrentresponseofGCE/PTh/MWCNT/{IOMN/Th}1ishigherthanthatofGCE/PTh/{IOMN/Th}1(Fig.4A).MWCNTs,here,couldincreasetheamountofimmobilizedIOMNsinadditiontoenhancingtheelec-tronshuttleabilityoftheelectrode.

TofurtherverifythattheelectrochemicalreductionofH2O2isduetoIOMNsotherthanMWCNTs,GCE/PTh/MWCNT/Thelectrodeswereconstructedtostudytheblankresponse.Theelectrocatalyt-icalreductionofMWCNTstoH2O2hasbeenreportedbymanygroups[9,21].Butinthiswork,nosigniﬁcantreductionsignalswereobservedatGCE/PTh/MWCNT/Thelectrodesfor1mMH2O2overthepotentialrangefrom−0.6to0.3V(notshown).Suchaphenomenoncanbeexplainedasfollows.SincethebackgroundcurrentisextremelyhighwhenalargeamountofMWCNTsareemployed,theconcentrationofMWCNTssolutionwasreducedheresoastoobtainarelativelylowbackgroundsignal.Thatis,onlysmallamountofMWCNTsweremodiﬁedontotheGCEsurface.Asaresult,theelectrocatalyticalreductionofH2O2byMWCNTswasverylimited.Therefore,theabovedatademonstratethatitisIOMNslayersnotMWCNTsthatplaytheprimaryroleintheelectrocatalyticreductiontoH2O2.

Accordingtothepreviousreports,themechanismoftheH2O2biosensorisbasedonthefollowingreactions[22]:H2O2+HRP→HRP-I+H2O

HRP-I+THH→HRP-II+TH→HRP+TH+TH++H++2e−→THH

TheH2O2isreducedinthepresenceofHRP;thenHRP-IisreducedtoHRPbyTHH(THHandTH+representreducedandoxidizedformsofthionin,respectively),andoxidizedTH+isreducedtoTHHattheelectrodesurface.

Thenumberofcatalyticlayersisaveryimportantaspecttobeconsideredwhendesigningmultilayerarchitectures.FurtherexperimentsalsoshowthatthecatalyticreductioncurrentofH2O2increaseswiththeincreaseinthelayernumberof{IOMN/Th}(Fig.4C,DandE).Itisfoundthat{IOMN/Th}3givesthehighestsen-sitivity.Thereductioncurrentof{IOMN/Th}4-modiﬁedelectrodes

Fig.5.CurrentresponsesofGCE/PTh/MWCNT/{IOMN/Th}3electrodesindifferentpHsolutionwith1mMH2O2.

toH2O2issmallerthanthatof{IOMN/Th}3duetothepossiblediffusionhinderance.TheLBLcovalentassemblyofmultilayersissuccessfulforpreparingasensitiveinterfaceduetoitsversatilitywiththerationaldesignofsensorsatmolecularlevel.Inaddition,themultilayer-modiﬁedelectrodeswerefoundtobestableduringthewholeelectrochemicalmeasurement.Thisfacileelectronacces-sibilityandthegoodstabilityoftheas-preparedmultilayerofferedthepossibilityforelectrochemicalcatalysis.

ThecatalyticactivityoftheIOMNs,likeHRP,isdepen-dentonpH.WemeasuredtheelectrocatalyticalreductionofGCE/PTh/MWCNT/{IOMN/Th}3electrodestoH2O2.TheoptimizedpHforthecatalyticcurrentofIOMNs-modiﬁedelectrodestoH2O2wasfoundataboutneutralorbasicsolution(Fig.5),whichisdif-ferentfromthepreviousreports[6,7].ThecombinationofMWCNT,PTh,IOMNs,andThmayformsthemicroenvironmentandaffectthecatalyticalperformanceofIOMNsontheelectrodesurface.

TheeffectsoftheappliedpotentialonthecurrentresponseofGCE/PTh/MWCNT/{IOMN/Th}3electrodehavealsobeenstudied(Fig.6).ThereductioncurrentresponsetoH2O2increasesrapidlywiththenegativeshiftoftheappliedpotentialstartingfrom0.3Vto−0.8V,andthenaslightdecreasecanbeobservedfrom−0.8to−0.9V.At−0.8V,theinterferencesignalfromO2becomesnegli-gible.Therefore,−0.5V(vs.Ag/AgCl)waschosenasanoptimizedworkingpotentialforbettersensitivityandlowerinterferencesig-nal.

Fig.6.EffectoftheappliedpotentialonthecurrentresponseofGCE/PTh/MWCNT/{IOMN/Th}3electrodeinthepresenceof1mMH2O2inpH8PBS(a)andthatsaturatedwithN2(b).

Y.Miaoetal./SensorsandActuatorsB138(2009)182–188187

Fig.7.CalibrationcurvesofGCE/PTh//MWCNT/{IOMN/Th}3electrodestoH2O2andtheamperometricresponseduringsuccessiveadditionof50␮l100mMor10mMH2O2into5mlpH8PBS.Conditionsof−0.5Vconstantpotential;pH8.0.

Fig.7showsthecalibrationcurvesandsteady-statecurrentresponseofGCE/PTh/MWCNT/{IOMN/Th}3electrodestoH2O2at−0.5V.AsshownintheinsetofFig.3,awell-deﬁnedresponsecanbeobservedduringthesuccessiveadditionofH2O2.AnextremelyattractivefeatureoftheGCE/PTh/MWCNT/{IOMN/Th}3electrodesisreﬂectedbytheirfastresponsetime(i.e.,<15s)towardH2O2,whichdemonstratesthatthesurface-conﬁnednanostructuredmultilayersareaccessibletotheanalytemoleculesandelectricallyconnectedwiththeunderlyingelectrode.Thecalibrationplotislinearoverthewideconcentrationrangeof0.099–6.54mMwithaslopeof2.74␮A/mM(sensitivity)andacorrelationcoefﬁcientof0.997.Thedetectionlimitoftheelectrodewasfoundtobe0.0536mMatasignal-to-noiseratioof3.OneoftheadvantagesoftheseIOMN-basedelectrodesforamperometricdetectionofH2O2istheirhighlystableamperometricresponse.Noobviousdecreaseinresponsewasobservedafter10daysstorageinroomtemperature.Therepeatabilityofresponseoftheconstructedelec-trodeswasinvestigatedataH2O2concentrationof1mM.Themeancurrentwas−3.54␮AwithanR.S.D.of6%(n=4).Sixmodiﬁedelec-trodes,preparedindependently,yieldedameancurrentresponseof−3.59␮AwithanR.S.D.of6.9%(n=4)at1mMH2O2.

Notethattheobtaineddetectionlimitscouldbeoptimizedfurthertoalowerlevel.DetailedstudiesontheoptimizationofIOMNs-modiﬁedelectrodesforH2O2andtheiruseforbiosensorapplicationsareunderway.4.Conclusion

IOMNswereemployedtodevelopamultilayerconstructionofGCE/PTh//MWCNT/{IOMN/Th}nelectrochemicalsensorsforH2O2assay.PolythioninwaselectrodepositedtofunctionalizetheGCEsurface.MWCNTs,IOMNsandthioninwereanchoredontoaPTh-modiﬁedGCEsurfacebycovalentbinding.WiththioninasmediatorandMWCNTsastheelectron-transferringbooster,theIOMNcatalysis-basedelectrodesexhibitexcellentelectrocatalyticalactivitytoH2O2.ThisapproachholdsgreatpromisingofpotentialapplicationsinvariousH2O2assay-basedbiosensorsinthefuture.Acknowledgements

ThismaterialisbaseduponworkfundedpartiallybytheNationalNaturalScienceFoundationofChina(GrantNo.90406016)andpartiallybyaLDRDprogramatPaciﬁcNorthwestNational

Laboratory(PNNL).TheworkwasperformedattheEnvironmen-talMolecularSciencesLaboratory,anationalscientiﬁcuserfacilitysponsoredbytheU.S.DepartmentofEnergy(DOE)andlocatedatPNNL.PNNLisoperatedbyBattelleforDOEunderContractDE-AC05-76RL01830.References

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Biographies

YuqingMiaoobtainedhisPhDdegreein2005fromWuhanTechnologyUniversity(China).Atpresent,heisaprofessorofZhejiangNormalUniversity(China).Theresearchmainlyfocusesonbiocatalysis,nanoelectrochemistryandelectrochemical

188Y.Miaoetal./SensorsandActuatorsB138(2009)182–188

biosensors.Thepresentresearchconcernsaboutconstructionofsmartbiomimicnanostructuresofacetylcholinesterasefortheassessmentofeffectsoforganophos-phatepoisoningonlivingenvironment.

HuaWang,hereceivedPhDdegreeinanalyticalchemistryfromHunanUniversityin2004.In2005hewasappointedasAssociateprofessoratHunanUniversity.Duringhiscareerhehaspublishedmorethan50articlesinpeerreviewedinternationaljournals.Atpresent,hismajorresearchactivitiesincludebiosensorsandadvancedfunctionalmaterials.

YuyanShaoreceivedhisPhDinAppliedChemistryfromHarbinInstituteofTech-nologyin2006.HeiscurrentlyapostdoctoralresearchassociateintheFundamentalSciencesDirectorateattheU.S.DOEPaciﬁcNorthwestNationalLaboratory.Hismaininterestsareintheﬁeldsofelectrocatalysis.

ZhiwenTangreceivedhisPhDmajoringinAnalyticalChemistryatHunanUniver-sity(China)onthetopicofDNA/RNAmolecularprobeengineering.HenowworksforPaciﬁcNorthwestNationalLaboratory.HisresearchinterestincludesDNA/RNAmolecularprobeengineering,aptamerselectionandfunctionalization,nanobiosen-sordevelopment.

JunWangcurrentlyisastaffscientistworkingintheChemistryandMaterialsGroupoftheFundamentalScienceDirectorateatthePaciﬁcNorthwestNationalLabora-tory(PNNL).PriortojoiningPNNL,hehadpostdoctoraltrainingintheDepartmentofPharmacologyattheUniversityofCaliforniaatLosAngeles(UCLA)andintheDepartmentofChemistryandBiochemistryattheCaliforniaStateUniversityatLosAngeles(CSULA).HeobtainedhisPhDdegreefromtheDepartmentofChemistryatWuhanUniversity,China.

YueheLinisalaboratoryfellowatPaciﬁcNorthwestNationalLaboratory.Hehasbeenactivelyworkinginthenanotechnologyarea,particularlyinthedevelopmentofnewnanobioelectronicdevicesandnanomaterialsforbiomedicaldiagnosisanddrugdelivery.Hisotherresearchactivitiesincludedevelopingintegratedmicroanalyti-calsystemsforenvironmentalandbiomedicalanalysis,andsynthesizingfunctionalnanomaterialsforbiosensordevelopment,fuelcell,andwatertreatmentapplica-tions.Dr.LinistheeditorofthebookHandbookofElectrochemicalNanotechnology.HealsoservesastheNorthAmericanEditorfortheJournalofNanoscienceandNan-otechnology,theassociateeditoroftheAdvancedScienceLetters,andMemberofEditorialAdvisoryBoardofother16internationaljournals.Dr.Linhasover200publications.

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