Biopotential-Electrodes：生物电的电极资料课件

Electrode–ElectrolyteInterface

Electrode

Electrolyte(neutralcharge)C+,A-insolutionCCCA-A-C+C+e-e-CurrentflowC+:Cation A-:Anion e-:electronFairlycommonelectrodematerials:Pt,Carbon,…,Au,Ag,…Electrodemetalisuseinconjunctionwithsalt,e.g.Ag-AgCl,Pt-Ptblack,orpolymercoats(e.g.Nafion,toimproveselectivity)Electrode–ElectrolyteInterfaceGeneralIonicEquationsa)Ifelectrodehassamematerialascation,thenthismaterialgetsoxidizedandenterstheelectrolyteasacationandelectronsremainattheelectrodeandflowintheexternalcircuit.b)Ifanioncanbeoxidizedattheelectrodetoformaneutralatom,oneortwoelectronsaregiventotheelectrode.a)b)Currentflowfromelectrodetoelectrolyte:Oxidation(Lossofe-)Currentflowfromelectrolytetoelectrode:Reduction(Gainofe-)Thedominatingreactioncanbeinferredfromthefollowing:HalfCellPotentialAcharacteristicpotentialdifferenceestablishedbytheelectrodeanditssurroundingelectrolytewhichdependsonthemetal,concentrationofionsinsolutionandtemperature(andsomesecondorderfactors).

Halfcellpotentialcannotbemeasuredwithoutasecondelectrode.Thehalfcellpotentialofthestandardhydrogenelectrodehasbeenarbitrarilysettozero.Otherhalfcellpotentialsareexpressedasapotentialdifferencewiththiselectrode.ReasonforHalfCellPotential:ChargeSeparationatInterfaceOxidationorreductionreactionsattheelectrode-electrolyteinterfaceleadtoadouble-chargelayer,similartothatwhichexistsalongelectricallyactivebiologicalcellmembranes.MeasuringHalfCellPotentialNote:Electrodematerialismetal+saltorpolymerselectivemembraneSomehalfcellpotentialsStandardHydrogenelectrodeNote:Ag-AgClhaslowjunctionpotential&itisalsoverystable->henceusedinECGelectrodes!PolarizationIfthereisacurrentbetweentheelectrodeandelectrolyte,theobservedhalfcellpotentialisoftenalteredduetopolarization.OverpotentialDifferencebetweenobservedandzero-currenthalfcellpotentialsResistanceCurrentchangesresistanceofelectrolyteandthus,avoltagedropresults.ConcentrationChangesindistributionofionsattheelectrode-electrolyteinterfaceActivationTheactivationenergybarrierdependsonthedirectionofcurrentanddetermineskineticsNote:Polarizationandimpedanceoftheelectrodearetwoofthemostimportantelectrodepropertiestoconsider.NernstEquationWhentwoaqueousionicsolutionsofdifferentconcentrationareseparatedbyanion-selectivesemi-permeablemembrane,anelectricpotentialexistsacrossthemembrane.Forthegeneraloxidation-reductionreactionTheNernstequationforhalfcellpotentialiswhereE0:StandardHalfCellPotential E:HalfCellPotentiala:IonicActivity(generallysameasconcentration)n:Numberofvalenceelectronsinvolved Note:interestedinionicactivityattheelectrode(butnotetempdependencePolarizableandNon-PolarizableElectrodesPerfectlyPolarizableElectrodesTheseareelectrodesinwhichnoactualchargecrossestheelectrode-electrolyteinterfacewhenacurrentisapplied.Thecurrentacrosstheinterfaceisadisplacementcurrentandtheelectrodebehaveslikeacapacitor.Example:Ag/AgClElectrodePerfectlyNon-PolarizableElectrodeTheseareelectrodeswherecurrentpassesfreelyacrosstheelectrode-electrolyteinterface,requiringnoenergytomakethetransition.Theseelectrodesseenooverpotentials.Example:PlatinumelectrodeExample:Ag-AgClisusedinrecordingwhilePtisuseinstimulationUseforrecordingUseforstimulationAg/AgClElectrodeAg+Cl-Cl2RelevantionicequationsGoverningNernstEquationSolubilityproductofAgClFabricationofAg/AgClelectrodesElectrolyticdepositionofAgClSinteringprocessformingpelletelectrodesEquivalentCircuitCd

:capacitanceofelectrode-eletrolyteinterfaceRd

:resistanceofelectrode-eletrolyteinterfaceRs:resistanceofelectrodeleadwireEcell:cellpotentialforelectrodeFrequencyResponseCornerfrequencyRd+RsRsElectrodeSkinInterfaceSweatglandsandductsElectrodeEpidermisDermisandsubcutaneouslayerRuEheRsRdCdGelReEseEPRPCPCeStratumCorneumSkinimpedancefor1cm2patch:200kΩ1Hz200Ω1MHzAlterskintransport(ordeliverdrugs)by:Poresproducedbylaser,ultrasoundorbyiontophoresis100m100mNerveendingsCapillaryMotionArtifactWhyWhentheelectrodemoveswithrespecttotheelectrolyte,thedistributionofthedoublelayerofchargeonpolarizableelectrodeinterfacechanges.Thischangesthehalfcellpotentialtemporarily.WhatIfapairofelectrodesisinanelectrolyteandonemoveswithrespecttotheother,apotentialdifferenceappearsacrosstheelectrodesknownasthemotionartifact.ThisisasourceofnoiseandinterferenceinbiopotentialmeasurementsMotionartifactisminimalfornon-polarizableelectrodesBodySurfaceRecordingElectrodesMetalPlateElectrodes(historic)SuctionElectrodes(historicinterest)FloatingElectrodesFlexibleElectrodesElectrodemetalElectrolyteThinkoftheconstructionofelectrosurgicalelectrodeAnd,howdoeselectro-surgerywork?CommonlyUsedBiopotentialElectrodesMetalplateelectrodesLargesurface:Ancient,thereforestillused,ECGMetaldiskwithstainlesssteel;platinumorgoldcoatedEMG,EEGsmallerdiametersmotionartifactsDisposablefoam-pad:Cheap!(a)Metal-plateelectrodeusedforapplicationtolimbs.

(b)Metal-diskelectrodeappliedwithsurgicaltape.

(c)Disposablefoam-padelectrodes,oftenusedwithECGCommonlyUsedBiopotentialElectrodesSuctionelectrodesNostrapsoradhesivesrequired

precordial(chest)ECGcanonlybeusedforshortperiodsFloatingelectrodesmetaldiskisrecessedswimmingintheelectrolytegelnotincontactwiththeskinreducesmotionartifactSuctionElectrodeDouble-sidedAdhesive-taperingInsulatingpackageMetaldiskElectrolytegelinrecess(a)(b)(c)SnapcoatedwithAg-AgClExternalsnapPlasticcupTackPlasticdiskFoampadCapillaryloopsDeadcellularmaterialGerminatinglayerGel-coatedspongeCommonlyUsedBiopotentialElectrodesFloatingElectrodesReusableDisposable(a)Carbon-filledsiliconerubberelectrode.

(b)Flexiblethin-filmneonatalelectrode.

(c)Cross-sectionalviewofthethin-filmelectrodein(b).

CommonlyUsedBiopotentialElectrodesFlexibleelectrodesBodycontoursareoftenirregularRegularlyshapedrigidelectrodesmaynotalwayswork.Specialcase:infantsMaterial:-Polymerornylonwithsilver-Carbonfilledsiliconrubber(Mylarfilm)InternalElectrodesNeedleandwireelectrodesforpercutaneousmeasurementofbiopotentials(a)Insulatedneedleelectrode.

(b)Coaxialneedleelectrode.

(c)Bipolarcoaxialelectrode.

(d)Fine-wireelectrodeconnected

tohypodermicneedle,before

beinginserted.

(e)Cross-sectionalviewofskin

andmuscle,showingcoiled

fine-wireelectrodeinplace.Thelatest:BION–implantedelectrodeformusclerecording/stimulationAlfredE.MannFoundationFetalECGElectrodesElectrodesfordetectingfetalelectrocardiogramduringlabor,bymeans

ofintracutaneousneedles(a)Suctionelectrode.(b)Cross-sectionalviewofsuctionelectrodeinplace,showingpenetrationofprobethroughepidermis.(c)Helicalelectrode,whichisattachedtofetalskinbycorkscrewtypeaction.ElectrodeArraysExamplesofmicrofabricatedelectrodearrays.

(a)One-dimensionalplungeelectrodearray,

(b)Two-dimensionalarray,and

(c)Three-dimensionalarrayContactsInsulatedleads(b)BaseAg/AgClelectrodesAg/AgClelectrodesBaseInsulatedleads(a)Contacts(c)TinesBaseExposedtipMicroelectrodesWhy

MeasurepotentialdifferenceacrosscellmembraneRequirementsSmallenoughtobeplacedintocellStrongenoughtopenetratecellmembraneTypicaltipdiameter:0.05–10micronsTypesSolidmetal->TungstenmicroelectrodesSupportedmetal(metalcontainedwithin/outsideglassneedle)Glassmicropipette->withAg-AgClelectrodemetalIntracellularExtracellularMetalMicroelectrodesExtracellularrecording–typicallyinbrainwhereyouareinterestedinrecordingthefiringofneurons(spikes).Usemetalelectrode+insulation->goestohighimpedanceamplifier…negativecapacitanceamplifier!Microns!RCMetalSupportedMicroelectrodes(a)Metalinsideglass (b)GlassinsidemetalGlassMicropipetteAglassmicropipetelectrodefilledwithanelectrolyticsolution

(a)Sectionoffine-boreglasscapillary.

(b)Capillarynarrowedthroughheatingandstretching.

(c)Finalstructureofglass-pipetmicroelectrode.

Intracellularrecording–typicallyforrecordingfromcells,suchascardiacmyocyteNeedhighimpedanceamplifier…negativecapacitanceamplifier!heatpullFillwithintracellularfluidor3MKClAg-AgClwire+3MKClhasverylowjunctionpotentialandhenceveryaccuratefordcmeasurements(e.g.actionpotential)ElectricalPropertiesofMicroelectrodesMetalmicroelectrodewithtipplacedwithincellEquivalentcircuitsMetalMicroelectrodeUsemetalelectrode+insulation->goestohighimpedanceamplifier…negativecapacitanceamplifier!ElectricalPropertiesofGlassIntracellularMicroelectrodesGlassMicropipetteMicroelectrodeStimulatingElectrodes–Cannotbemodeledasaseriesresistanceandcapacitance(thereisnosingleusefulmodel)–

Thebody/electrodehasahighlynonlinearresponsetostimulation–Largecurrentscancause –

Cavitation –

Celldamage –

HeatingTypesofstimulatingelectrodesPacingAblationDefibrillationFeaturesPlatinumelectrodes:Applications:neuralstimulationModerndayPt-Irandotherexoticmetalcombinationstoreducepolarization,improveconductanceandlonglife/biocompatibilitySteelelectrodesforpacemakersanddefibrillatorsIntraocularStimulationElectrodesReference:LutzHesse,ThomasSchanze,MarcusWilmsandMarcusEger,“Implantationofretinastimulationelectrodesandrecordingofelectricalstimulationresponsesinthevisualcortexofthecat”,Graefe’sArchClinExpOphthalmol(2000)238:840–845Invivoneuralmicrosystems(FIBE):challengeInvivoneuralmicrosystems(FIBE):biocompatibility-variantInvivoneuralmicrosystems(FIBE):stateoftheartNeuralmicroelectrodesMEMS-MicrosystemsInstrumentationforneurophysiologyNeuralMicrosystemsIntroduction:neuralmicrosystems–––––ExternalelectrodesSubduralelectrodesMicro-electrodesMicrosensorsHumanlevelAnimallevelTissueslicelevelCellularlevelIntroduction:typesofneuralmicrosystemsapplicationsInvivoapplicationsInvitroapplicationsMicroelectronictechnology

forMicroelectrodesBondingpadsSisubstrateExposedtipsLeadviaChannelsElectrodeSiliconprobeSiliconchipMiniatureinsulatingchamberContactmetalfilmHoleSiO2insulatedAuprobesSiliconprobeExposedelectrodesInsulatedleadvias(b)(d)(a)(c)Differenttypesofmicroelectrodesfabricatedusingmicrofabrication/MEMStechnologyBeam-leadmultipleelectrode.MultielectrodesiliconprobeMultiple-chamberelectrodePeripheral-nerveelectrodeMichiganProbesforNeuralRecordingsNeuralRecordingMicroelectrodesReference:acreo.se/acreo-rd/IMAGES/PUBLICATIONS/PROCEEDINGS/ABSTRACT-KINDLUNDH.PDFInvivoneuralmicrosystems:3examplesUniversityofMichiganSmartcomb-shapemicroelectrodearraysforbrainstimulationandrecordingUniversityofIllinoisatUrbana-ChampaignHigh-densitycomb-sha