UltramicroelectrodesElectroanalyticalChemistryLecture#7UltramicroelectrodesElectroanaUME’sGeometriesDiskRecesseddisk

C.S.Henry;I.FritschAnal.Chem.

1999,71,550-6.BandCylinderMaterialsCarbonfiberUME’sGeometriesUME’s-AdvantagesReducedcapacitance

LowiRdropUME’s-AdvantagesReducedcapaUME’s-DisadvantagesNoiseElectrochemicalFoulingAnalyteMethodofelectrodeprep’n(epoxy)StraycapacitanceImpuritiesMaintenanceCostFragileconstructionUME’s-DisadvantagesNoiseUME’s-ApplicationsDetermine[analyte]Studyreactionsatlowtemperatures=frozenglassesinsolventsofmoderatetohighpermittivityw/oelectrolyteinsolventsofhighresistanceinsolidstateingasphaseUME’s-ApplicationsDetermineUME’s-Applications(cont’d)BiologicalsystemsSinglecellsorganellesFastkineticsDevelopmentofanalyticaltoolsforelectrode/solutioninterfaceSECM(Bard)EQCMSERS(VanDuyne)UME’s-Applications(cont’d)BScanningElectrochemicalMicroscopy(SECM)Diffusionishemisphericaliss=4nFCo*Doa

wherea=diam.ofUMEAcquireIvs.tipposition(x,y)Plotofdvs.tippositionpiezoelectricpositioningBipotentiostatSampleCWRRef.:Bardetal.

Science

1991,254,68-74.dScanningElectrochemicalMicroSECM(cont’d)W-100nm(diam.)Determinesresolution2nmbestatpresentSampleConductingInsulatorMineralBiologicalSemiconductorSampleCWRSECM(cont’d)W-100nm(diam.CommonModesofOperationFeedbackPositiveornegative

Collectionfluxofspeciesgenerated/consumedprobedCommonModesofOperationFeedbSECM-PositiveFeedbackIfsampleconductive,

wegetpositivefeedback

i>issConductiveSampleCWRROSECM-PositiveFeedbackIfsampSECM-NegativeFeedbackIfsampleinsulator,

wegetnegativefeedback

i<issDiffusionishinderedInsulatorSampleCWRROOOOSECM-NegativeFeedbackIfsamSECM-OperationConstantheightmodetipscannedacrosssubstrate,currentmonitoredInsitucanbedoneinmoistairSECM-OperationConstantheighSECM-ApplicationsAnalysis

Imaging

NanolithographyhighprecisionhighaccuracySECM-ApplicationsAnalysis

SECM:ReviewsR.C.Engstrom,C.M.PharrAnal.Chem.

1989,61,1099A-1104A.A.J.Bard,G.Denuault,C.Lee,D.Mandler,D.O.WipfAcc.Chem.Res.

1990,23,357-363.M.V.MirkinAnal.Chem.

1996,96,177A-182A.SECM:ReviewsR.C.Engstrom,C.ElectrochemicalQuartzCrystalMicrobalances(EQCM)Verysensitivemasssensorssubmonolayer

Design:2electrodessandwichingquartz(piezoelectric)oscillatingEsurfaceofquartzwaferoscillationatcharacteristicfrequency(2-20MHz)electrodeelectrodeQuartzcrystalstuffElectrochemicalQuartzCrystalEQCM-PrinciplesofOperationMeasurechangeinoscillationfrequencySauerbreyequation:

f=-2(m/A)nfo2/(quartzquartz)1/2

where

n=overtonenumber

quartz=shearmodulus(2.95x1011g/cms)

quartz=density(2.65g/cm3)EQCM-PrinciplesofOperationEQCM-PrinciplesofOperation(cont’d)Sauerbreyequation:f=-2(m/A)nfo2/(quartzquartz)1/2Significance:ifmpositive,thenf________ifmnegative,thenf________for300mthickquartzwaferoscillatingat5MHzandm=18ng/cm2f1Hz(measurable)EQCM-PrinciplesofOperationEQCM-PrinciplesofOperationSolutionexertsadampeningeffect:

f=-f03/2[solnsoln/(qaurtzquartz)]1/2

where:

soln=solutionviscosity

soln=solutiondensityEQCM-PrinciplesofOperationEQCM-AdvantagesSensitivityng/cm2Hz

Insitutechniquenotavacuummethod

Inexpensive<$10kEQCM-AdvantagesSensitivityEQCM-DisadvantagesSelectivitymasssensorCannotdistinguishwhatisonsurfaceEQCM-DisadvantagesSelectivitEQCM-ApplicationsMechanismofElectrochemical/SurfacephenomenaUnderpotentialdeposition(UPD)DepositionoffirstmonolayeratEpositiveofEoElectroprecipitationpolymersprep’delectrochemicallydifferentfromthatprep’dbyothermethodsEQCM-ApplicationsMechanismoSurface-enhancedRamanScattering(SERS)1974R.VanDuyne(Northwestern)Enhancement1012-1014comp’dtononresonantRamanSurface-enhancedRamanScatterSERS-AdvantagesInsituUnderpotentialcontrolXPS,SEM,etc.notinsituVerysensitiveGoodforcomplexmatricesPhysiologicalfluidsDetectionlimitpmole-fmoletraceanalysisSERS-AdvantagesInsituSERS-Advantages(cont’d)VeryselectiveOnlymoleculesat/nearsurfaceprobed(upto16nm)SurfacespecificityVibrationalstructuralprobeInfoonorientationwrtsurfaceSERS-Advantages(cont’d)VerySERS-DisadvantagesReproducibilityTheoreticalunderstandingofunderlyingmechanismsincompleteLimitsquantitationLimitednumberofsuitablesubstratesCu,Ag,Au-bestSERS-DisadvantagesReproducibRaman-History1928-C.V.Raman,physicistC.V.RamanandK.S.Krishnan,Nature1928,121,50.“ANewTypeofSecondaryRadiation”1930NobelPrizehttp://www.rri.res.in/Raman-History1928-C.V.RamRaman-MechanismRelativeIntensityFrequencyincidentincident+’incident-’StokesAnti-StokesE=0=0=1=1virtualvirtualFewermoleculesinv=1atRT(kT)Lessintensebecauselessprobableeventhincidenth(incident-’)BeforeAfterRaman-MechanismRelativeInteRamanI(ij)2ETensoralIsotropicIfwanttoincreaseIthenincreaseij(molecular)ERamanI(ij)2EResonanceRaman(RR)Molecularmechanism:ij=A/(-o+i)+B/(+o+i)Resonance

when=oAtermblowsupImparts:SelectivitySensitivityResonanceRaman(RR)MolecularRaman-HowisitDone?lasermonochromatorCCDCameralensSpinningsamplescramblergratingRaman-HowisitDone?lasermoSERS-3MechanismsElectromagnetic(EM)-MoskovitsDominantPreferentialutilityofCu,Ag,AuImageField-Schatz,vanDuyneSelectionrulesAdatom-OttoSERS-3MechanismsElectromagnElectromagneticFornobleMwithroughness<lightConfiguration:d10s1OuterelectronbehavesasfreeelectronSignificance:haslargenegativerealcomponentandsmallimaginarycomponentAg:()-2ElectromagneticFornobleMwitElectromagneticLocalEforsphericalparticleofnobleMis:Elocal=Eo(()+2)-1

so,ElocalisverylargeIfelliptical:Elocal=Eo(1+A[()-1])-1themoreelliptical,thesmallerASignificance:mustgotolongerElectromagneticLocalEforsphImageDipoleFreeelectronsoscillatewithEincidentandpolarizeMcreatingintensesurfaceEplasmoninducingadipoleintheanalytehParallel:CancelhPerpendicular:AddImageDipoleFreeelectronsoscAdatomChemicalresonanceeffectAg+compound=newcompoundEvidence:AgpyridiniumsaltsAdatomChemicalresonanceeffecSERS-HowDone?EnhancementElectrochemicallyOxidation-reductioncycle(ORC)oxidize/reduceMinpresenceofanalyteAg/AucolloidsPotentiostat-ifelectrochemicalRamanspectrometerLaserMonochromatorCCDdetectorSERS-HowDone?EnhancementEXAMPLE:SERSDetectionof2,4-DNTasMarkerforLandminesInsanity:Installation:removal-30:1(1995)$33B,1100yrsforremovalChallenges:Time,cost,falsepositivesContent:>99%TNTdegradationproducts:2,4-DNT,1,3-DNB(volatile)J.M.Sylvia,J.A.Janni,J.D.Klein,K.M.SpencerAnal.Chem.

2000,72,5834-40./gallery/landmines/;photosbyNicDunlopEXAMPLE:SERSDetectionof2,EXAMPLE:Cont’dProposal:Ramanvapor“sniffer”Instrument:Diodelaser(exc=785nm;100mW)withfiberopticprobeEchellespectrographCCDcamera(aircooled)SERS:Aufoil(-0.3-1.2V@500mV/sORC)Detectionof<20ppb2,4-DNTin30sEXAMPLE:Cont’dProposal:RamSERSReviewsR.M.BaumC&ENews1983(Oct.3),22-24.T.M.CottonInSpectroscopyofSurfacesR.J.H.Clark,R.E.Hester,Eds.,Wiley,1988,91-153.R.L.GarrellAnal.Chem.

1989,61,401A-411A.M.J.Weaver,S.Zou,H.Y.H.ChanAnal.Chem.2000,72,38A-47A.SERSReviewsR.M.BaumC&ENewsBioelectrochemistryRelativelynewfieldEarly‘80’sDatesfrom1958:KonoandNakamuraCytc/PtreductionelectrochemicallyirreversibleBioelectrochemistryRelativelyMostWorkonHemeproteinsMono-hemeCytochromec(H.A.O.Hill,Hawkridge)Myoglobin(Rusling,Taniguchi)Several-hemeCytochromec3(Nikki)Hemoglobin(S.Dong)HemepeptidesMicroperoxidase-8,-11(Santucci,Kulys)Enzymes(F.Armstrong)MostWorkonHemeproteinsProtein/ElectrodesPreparedUsingPhysicalimmobilizationAdsorptionInclusionSol-gelsChemicalimmobilizationCross-linkingGluteraldehyde(justlikeinx-ray)PolymericfilmPolypyrrole(conductingpolymer)NafionProtein/ElectrodesPreparedUsMostWorkDoneUsingElectrodeMaterialsMetals(Au,Pt)CarbonGlassy(GC)Pyrolyticgraphite(PG)Opticallytransparent(In-SnO2/glass)(ITO)NewMaterialsBoron-dopeddiamond(BDD)MostWorkDoneUsingElectrodeApproachestoBioelectrochemistryDirectProtein/Electrode(Hawkridge,Rusling)Protein/Promoter/Electrode(Hill)4,4’-bipyridinebis(4-pyridyl)disulfide(BPD)MediatedProtein/Mediator/ElectrodeChemically-modifiedProtein/Electrode(Heller)FerroceneDyes(S.Dong)ApproachestoBioelectrochemisProblemsforDirectElectrochemistryIrreversibleadsorptionFirstevidence-SERS(Cotton)DenaturationFoulingFewsystemscanbeoxidized/reducedSluggishelectrontransferratesProblemsforDirectElectrochePurificationisImportant1982-Cytochromec(FW12,384)FirstindicationthatdirectbioelectrochemistrypossibleatnakedelectrodeBowden,E.F.;Hawkridge,F.M.;Chlebowski,J.F.Bancroft,E.E.;Thorp,C.;Blount,H.N.J.Am.Chem.Soc.

1982,104,7641-4.1CRC:Sanishvili,R.,Volz,K.W.,Westbrook,E.M.,Margoliash,E.Structure3pp.707(1995)PurificationisImportant1982Promoters1979firstreportofdirectelectrochemistryforcytc/Aumodifiedwith4,4’-bpyor1,2-bis(4-pyridyl)ethylenepromoter-notdirectlyinvolvedinelectrontransferEddowes,M.J.;Hill,H.A.O.J.Am.Chem.Soc.

1979,101,4461-2.Armstrong,F.A.;Hill,H.A.O.;Walton,N.J.Q.Rev.Biophys.

1986,3,261-322.electrodeCytcPromoters1979firstreportofPurificationisImportant1993-Mb(FW17,000)infilmofdidodecyldimethyl-ammoniumbromide(DDAB)/Pt,In-SnO2,Au1995-ultrafiltrationusedtoremovedimer(FW34,000)Rusling,J.F.;Nassar,A.F.J.Am.Chem.Soc.1993,115,11891-7.Nassar,A.F.;Willis,W.S.;Rusling,J.F.Anal.Chem.

1995,67,2386-92.PurificationisImportant1993HorseMyoglobinStructure:FW17,5006-cHSheme;axialligands:His,H2OFunction:oxygenstorageandtransportFe3++e-=Fe2+ -140mVvs.Ag/AgClMb(III)H2O+e-=Mb(II)+H2O

(aquo)met deoxy

6-c 5-cQ:DoesH2Odissociatebeforeorafterreductiveelectrontransfer?1YMB:Evans,S.V.,Brayer,G.D.:High-resolutionstudyofthethree-dimensionalstructureofhorseheartmetmyoglobin.J.Mol.Biol.213pp.885(1990)HorseMyoglobinStructure:1YMB:MbElectrochemicalCharacteristicsaTaniguchi,1992bTaniguchi,1999cRusling,1993MbElectrochemicalCharacterisSpectroelectrochemicalCharacterizationisEssentialClassiccase:1997GuadalupeHRP/GCfromDMSOorDMF

HRPdenaturesinDMSOandDMF

Moral:spectroscopyandelectrochemicalstudymustbeaccomplishedinconcertGuo,Y.;Guadalupe,A.R.Chem.Commun.

1997,1437-8.SpectroelectrochemicalCharactCofactorsNicotinamideadeninedinucleotide(NADH)sawearlierFlavinadeninedinucleotide(FADH)CofactorsNicotinamideadenineCofactors-NADHNicotinamideadeninedinucleotide(NADH)Significance:Co-factorfor>300dehydrogenaseenzymesChallenges:ElectrochemicaloxidationIrreversibleadsorptionofNAD+Electrodedeactivation(shorttermstability)Highovervoltage(>1V)Abruna,H.see:Anal.Chem.

1995,67,3936-44.;Anal.Chem.1996,68,3688-96.;Anal.Chem.1997,69,4065-75.Cofactors-NADHNicotinamideaOxidationofNADHatBDDDevicecharacteristics:Detectionlimit10nM(n=7)Stability-3mos.Interferents-ascorbicacid(correctable)OxidationofNADHatBDDDeviceBioelectrochemistry:TheExacTechGlucoseElectrodeAmperometricBiosensor:MediatedelectrontransferelectrodesurfaceFc+FcFcGluOxGluOxGluOxglucoseglucolactone

+2H+2e-+0.5V-0.1Ve-Idea:measurecurrentwhichiscorrelatedwith[Glucose]Bioelectrochemistry:TheExacSBPIsolablefromsoybeanseedcoatsoybeanU.S.cashcropseedcoatiswasteproductSingleisozymevs.mixture(HRP)BroadpHstabilitycatalyticallyactivefrompH2-8ThermostableatelevatedtemperaturesU.S.SoybeanCropValue1974-1999$MillionStatistics:/;photo:/csi/SBPIsolablefromsoybeanseedApplicationsUsingSBPMedicaldiagnosticsBiocatalysismanufactureofphenolicresins(LCD’s,microelectronics,epoxy,plastics,etc.)HaircoloringWastewatertreatmentremovalofphenolfromwastewaterandsludgeApplicationsUsingSBPMedicalSBPSol-GelH2O2SensorNeed:H2O2sensorforlowpHmediaFood,fermentation

Approach:Enzymeencapsulated(sol-gel)/GCMethyleneblue-dyemediatorWang,B.;Li,B.;Wang,Z.;Xu,G.;Wang,Q.;Dong,S.Anal.Chem.

1999,71,1935-9.SBPSol-GelH2O2SensorNeed:SBPSol-GelH2O2SensorDevicecharacteristics:Responsetime-5s(fastdiffusion)BroadpHresponse(3-7)Highsensitivity(27.5A/mM)Linearity(0.02-2.6mM)Detectionlimit(0.5M)Reproducibility(1.2%RSDforn=7at0.2mM)Interferentssulfide,ascorbate,fluorideWang,B.;Li,B.;Wang,Z.;Xu,G.;Wang,Q.;Dong,S.Anal.Chem.

1999,71,1935-9.SBPSol-GelH2O2SensorDeviceUltramicroelectrodesElectroanalyticalChemistryLecture#7UltramicroelectrodesElectroanaUME’sGeometriesDiskRecesseddisk

C.S.Henry;I.FritschAnal.Chem.

1999,71,550-6.BandCylinderMaterialsCarbonfiberUME’sGeometriesUME’s-AdvantagesReducedcapacitance

LowiRdropUME’s-AdvantagesReducedcapaUME’s-DisadvantagesNoiseElectrochemicalFoulingAnalyteMethodofelectrodeprep’n(epoxy)StraycapacitanceImpuritiesMaintenanceCostFragileconstructionUME’s-DisadvantagesNoiseUME’s-ApplicationsDetermine[analyte]Studyreactionsatlowtemperatures=frozenglassesinsolventsofmoderatetohighpermittivityw/oelectrolyteinsolventsofhighresistanceinsolidstateingasphaseUME’s-ApplicationsDetermineUME’s-Applications(cont’d)BiologicalsystemsSinglecellsorganellesFastkineticsDevelopmentofanalyticaltoolsforelectrode/solutioninterfaceSECM(Bard)EQCMSERS(VanDuyne)UME’s-Applications(cont’d)BScanningElectrochemicalMicroscopy(SECM)Diffusionishemisphericaliss=4nFCo*Doa

wherea=diam.ofUMEAcquireIvs.tipposition(x,y)Plotofdvs.tippositionpiezoelectricpositioningBipotentiostatSampleCWRRef.:Bardetal.

Science

1991,254,68-74.dScanningElectrochemicalMicroSECM(cont’d)W-100nm(diam.)Determinesresolution2nmbestatpresentSampleConductingInsulatorMineralBiologicalSemiconductorSampleCWRSECM(cont’d)W-100nm(diam.CommonModesofOperationFeedbackPositiveornegative

Collectionfluxofspeciesgenerated/consumedprobedCommonModesofOperationFeedbSECM-PositiveFeedbackIfsampleconductive,

wegetpositivefeedback

i>issConductiveSampleCWRROSECM-PositiveFeedbackIfsampSECM-NegativeFeedbackIfsampleinsulator,

wegetnegativefeedback

i<issDiffusionishinderedInsulatorSampleCWRROOOOSECM-NegativeFeedbackIfsamSECM-OperationConstantheightmodetipscannedacrosssubstrate,currentmonitoredInsitucanbedoneinmoistairSECM-OperationConstantheighSECM-ApplicationsAnalysis

Imaging

NanolithographyhighprecisionhighaccuracySECM-ApplicationsAnalysis

SECM:ReviewsR.C.Engstrom,C.M.PharrAnal.Chem.

1989,61,1099A-1104A.A.J.Bard,G.Denuault,C.Lee,D.Mandler,D.O.WipfAcc.Chem.Res.

1990,23,357-363.M.V.MirkinAnal.Chem.

1996,96,177A-182A.SECM:ReviewsR.C.Engstrom,C.ElectrochemicalQuartzCrystalMicrobalances(EQCM)Verysensitivemasssensorssubmonolayer

Design:2electrodessandwichingquartz(piezoelectric)oscillatingEsurfaceofquartzwaferoscillationatcharacteristicfrequency(2-20MHz)electrodeelectrodeQuartzcrystalstuffElectrochemicalQuartzCrystalEQCM-PrinciplesofOperationMeasurechangeinoscillationfrequencySauerbreyequation:

f=-2(m/A)nfo2/(quartzquartz)1/2

where

n=overtonenumber

quartz=shearmodulus(2.95x1011g/cms)

quartz=density(2.65g/cm3)EQCM-PrinciplesofOperationEQCM-PrinciplesofOperation(cont’d)Sauerbreyequation:f=-2(m/A)nfo2/(quartzquartz)1/2Significance:ifmpositive,thenf________ifmnegative,thenf________for300mthickquartzwaferoscillatingat5MHzandm=18ng/cm2f1Hz(measurable)EQCM-PrinciplesofOperationEQCM-PrinciplesofOperationSolutionexertsadampeningeffect:

f=-f03/2[solnsoln/(qaurtzquartz)]1/2

where:

soln=solutionviscosity

soln=solutiondensityEQCM-PrinciplesofOperationEQCM-AdvantagesSensitivityng/cm2Hz

Insitutechniquenotavacuummethod

Inexpensive<$10kEQCM-AdvantagesSensitivityEQCM-DisadvantagesSelectivitymasssensorCannotdistinguishwhatisonsurfaceEQCM-DisadvantagesSelectivitEQCM-ApplicationsMechanismofElectrochemical/SurfacephenomenaUnderpotentialdeposition(UPD)DepositionoffirstmonolayeratEpositiveofEoElectroprecipitationpolymersprep’delectrochemicallydifferentfromthatprep’dbyothermethodsEQCM-ApplicationsMechanismoSurface-enhancedRamanScattering(SERS)1974R.VanDuyne(Northwestern)Enhancement1012-1014comp’dtononresonantRamanSurface-enhancedRamanScatterSERS-AdvantagesInsituUnderpotentialcontrolXPS,SEM,etc.notinsituVerysensitiveGoodforcomplexmatricesPhysiologicalfluidsDetectionlimitpmole-fmoletraceanalysisSERS-AdvantagesInsituSERS-Advantages(cont’d)VeryselectiveOnlymoleculesat/nearsurfaceprobed(upto16nm)SurfacespecificityVibrationalstructuralprobeInfoonorientationwrtsurfaceSERS-Advantages(cont’d)VerySERS-DisadvantagesReproducibilityTheoreticalunderstandingofunderlyingmechanismsincompleteLimitsquantitationLimitednumberofsuitablesubstratesCu,Ag,Au-bestSERS-DisadvantagesReproducibRaman-History1928-C.V.Raman,physicistC.V.RamanandK.S.Krishnan,Nature1928,121,50.“ANewTypeofSecondaryRadiation”1930NobelPrizehttp://www.rri.res.in/Raman-History1928-C.V.RamRaman-MechanismRelativeIntensityFrequencyincidentincident+’incident-’StokesAnti-StokesE=0=0=1=1virtualvirtualFewermoleculesinv=1atRT(kT)Lessintensebecauselessprobableeventhincidenth(incident-’)BeforeAfterRaman-MechanismRelativeInteRamanI(ij)2ETensoralIsotropicIfwanttoincreaseIthenincreaseij(molecular)ERamanI(ij)2EResonanceRaman(RR)Molecularmechanism:ij=A/(-o+i)+B/(+o+i)Resonance

when=oAtermblowsupImparts:SelectivitySensitivityResonanceRaman(RR)MolecularRaman-HowisitDone?lasermonochromatorCCDCameralensSpinningsamplescramblergratingRaman-HowisitDone?lasermoSERS-3MechanismsElectromagnetic(EM)-MoskovitsDominantPreferentialutilityofCu,Ag,AuImageField-Schatz,vanDuyneSelectionrulesAdatom-OttoSERS-3MechanismsElectromagnElectromagneticFornobleMwithroughness<lightConfiguration:d10s1OuterelectronbehavesasfreeelectronSignificance:haslargenegativerealcomponentandsmallimaginarycomponentAg:()-2ElectromagneticFornobleMwitElectromagneticLocalEforsphericalparticleofnobleMis:Elocal=Eo(()+2)-1

so,ElocalisverylargeIfelliptical:Elocal=Eo(1+A[()-1])-1themoreelliptical,thesmallerASignificance:mustgotolongerElectromagneticLocalEforsphImageDipoleFreeelectronsoscillatewithEincidentandpolarizeMcreatingintensesurfaceEplasmoninducingadipoleintheanalytehParallel:CancelhPerpendicular:AddImageDipoleFreeelectronsoscAdatomChemicalresonanceeffectAg+compound=newcompoundEvidence:AgpyridiniumsaltsAdatomChemicalresonanceeffecSERS-HowDone?EnhancementElectrochemicallyOxidation-reductioncycle(ORC)oxidize/reduceMinpresenceofanalyteAg/AucolloidsPotentiostat-ifelectrochemicalRamanspectrometerLaserMonochromatorCCDdetectorSERS-HowDone?EnhancementEXAMPLE:SERSDetectionof2,4-DNTasMarkerforLandminesInsanity:Installation:removal-30:1(1995)$33B,1100yrsforremovalChallenges:Time,cost,falsepositivesContent:>99%TNTdegradationproducts:2,4-DNT,1,3-DNB(volatile)J.M.Sylvia,J.A.Janni,J.D.Klein,K.M.SpencerAnal.Chem.

2000,72,5834-40./gallery/landmines/;photosbyNicDunlopEXAMPLE:SERSDetectionof2,EXAMPLE:Cont’dProposal:Ramanvapor“sniffer”Instrument:Diodelaser(exc=785nm;100mW)withfiberopticprobeEchellespectrographCCDcamera(aircooled)SERS:Aufoil(-0.3-1.2V@500mV/sORC)Detectionof<20ppb2,4-DNTin30sEXAMPLE:Cont’dProposal:RamSERSReviewsR.M.BaumC&ENews1983(Oct.3),22-24.T.M.CottonInSpectroscopyofSurfacesR.J.H.Clark,R.E.Hester,Eds.,Wiley,1988,91-153.R.L.GarrellAnal.Chem.

1989,61,401A-411A.M.J.Weaver,S.Zou,H.Y.H.ChanAnal.Chem.2000,72,38A-47A.SERSReviewsR.M.BaumC&ENewsBioelectrochemistryRelativelynewfieldEarly‘80’sDatesfrom1958:KonoandNakamuraCytc/PtreductionelectrochemicallyirreversibleBioelectrochemistryRelativelyMostWorkonHemeproteinsMono-hemeCytochromec(H.A.O.Hill,Hawkridge)Myoglobin(Rusling,Taniguchi)Several-hemeCytochromec3(Nikki)Hemoglobin(S.Dong)HemepeptidesMicroperoxidase-8,-11(Santucci,Kulys)Enzymes(F.Armstrong)MostWorkonHemeproteinsProtein/ElectrodesPreparedUsingPhysicalimmobilizationAdsorptionInclusionSol-gelsChemicalimmobilizationCross-linkingGluteraldehyde(justlikeinx-ray)PolymericfilmPolypyrrole(conductingpolymer)NafionProtein/ElectrodesPreparedUsMostWorkDoneUsingElectrodeMaterialsMetals(Au,Pt)CarbonGlassy(GC)Pyrolyticgraphite(PG)Opticallytransparent(In-SnO2/glass)(ITO)NewMaterialsBoron-dopeddiamond(BDD)MostWorkDoneUsingElectrodeApproachestoBioelectrochemistryDirectProtein/Electrode(Hawkridge,Rusling)Protein/Promoter/Electrode(Hill)4,4’-bipyridinebis(4-pyridyl)disulfide(BPD)MediatedProtein/Mediator/ElectrodeChemically-modifiedProtein/Electrode(Heller)FerroceneDyes(S.Dong)ApproachestoBioelectrochemisProblemsforDirectElectrochemistryIrreversibleadsorptionFirstevidence-SERS(Cotton)DenaturationFoulingFewsystemscanbeoxidized/reducedSluggishelectrontransferratesProblemsforDirectElectrochePurificationisImportant1982-Cytochromec(FW12,384)FirstindicationthatdirectbioelectrochemistrypossibleatnakedelectrodeBowden,E.F.;Hawkridge,F.M.;Chlebowski,J.F.Bancroft,E.E.;Thorp,C.;Blount,H.N.J.Am.Chem.Soc.

1982,104,7641-4.1CRC:Sanishvili,R.,Volz,K.W.,Westbrook,E.M.,Margoliash,E.Structure3pp.707(1995)PurificationisImportant1982Promoters1979firstreportofdirectelectrochemistryforcytc/Aumodifiedwith4,4’-bpyor1,2-bis(4-pyridyl)ethylenepromoter-notdirectlyinvolvedinelectrontransferEddowes,M.J.;Hill,H.A.O.J.Am.Chem.Soc.

1979,101,4461-2.Armstrong,F.A.;Hill,H.A.O.;Walton,N.J.Q.Rev.Biophys.

1986,3,261-322.electrodeCytcPromoters1979firstreportofPurificationisImportant1993-Mb(FW17,000)infilmofdidodecyldimethyl-ammoniumbromide(DDAB)/Pt,In-SnO2,Au1995-ultrafiltrationusedtoremovedimer(FW34,000)Rusling,J.F.;Nassar,A.F.J.Am.Chem.Soc.1993,115,11891-7.Nassar,A.F.;Willis,W.S.;Rusling,J.F.Anal.Chem.

1995,67,2386-92.PurificationisImportant1993HorseMyoglobinStructure:FW17,5006-cHSheme;axialligands:His,H2OFunction:oxygenstorageandtransportFe3++e-=Fe2+ -140mVvs.Ag/AgClMb(III)H2O+e-=Mb(II)+H2O

(aquo)met deoxy

6-c 5-cQ:DoesH2Odissociatebeforeorafterreductiveelectrontransfer?1YMB:Evans,S.V.,Brayer,G.D.:High-resolutionstudyofthethree-dimensionalstructureofhorseheart