Flexible Microsensor Array for the Monitoring and

IntelligentMicrosystemLaboratoryUniversityofMissouri-Rolla1FlexibleMicrosensorArrayfortheMonitoringandControlofPlantGrowthSystemChang-SooKim1,2,D.MarshallPorterfield2,1,H.TroyNagle3,ChristopherS.Brown4(1)Dept.ofElectrical&ComputerEngineering,UniversityofMissouri-Rolla(2)Dept.ofBiologicalSciences,UniversityofMissouri-Rolla(3)Dept.ofElectrical&ComputerEngineering,NorthCarolinaStateUniversity(4)KenanInstituteforEngineering,Technology,&Science,NorthCarolinaStateUniversityIntelligentMicrosystemLaboratoryUniversityofMissouri-Rolla2Plantgrowthplatforminmicrogravity•Nutrientsolutiondeliveryusingporouslayer;capillaryinterfacebetweenrootandsolution.•Criticalneedofprecisecontrolofrhizosphere(root-environmentinteractions);wetness,oxygen,nutrients,temperature,etc.NutrientsolutionPoroustube(ceramic)IntelligentMicrosystemLaboratoryUniversityofMissouri-Rolla3Requirementsforsensorsinmonitoringandcontrolofrootzone•Idealconfiguration;miniaturization,multiple,lowpowerconsumption,robustnessandstability.•DependableInsitudiagnosisand/orcalibrationmethod;maintenanceofaccuracyandfunctionality.•Microsensorsfordissolvedoxygenandwetnessdetection.IntelligentMicrosystemLaboratoryUniversityofMissouri-Rolla4Electrochemicalmicroelectrodesonpolyimide(Kapton®)substrate(3-electrodepolarographicoxygensensor)•Substrate:Kapton(polyimide)•Metal(Pt)andlithography•Polyimidelithography(thin)•Polyimidelithography(thick)AE/CEREAEWEAERECEAE/Polyimide(thick)Polyimide(thin)KaptonsubstratePoly-HEMA(hydrogel)IntelligentMicrosystemLaboratoryUniversityofMissouri-Rolla5Microsensorarraysonflexiblesubstrates•Oxygenmicrosensorstrip(3-electrodeelectrochemicalmeasurement)•Conductivitysensorstrip(4-electrodeimpedancemeasurement)3inchesIntelligentMicrosystemLaboratoryUniversityofMissouri-Rolla6Poroustube-microsensorinterface(animation)•Microsensorarrayonaflexiblesubstrateenwrappingaporoustube.•Oxygenmicrosensor;dissolvedoxygendetection.•4-pointmicroprobe:surfacewetnessdetection.NutrientsolutionNutrientsolutionOxygenmicrosensorFlexiblesubstratePoroustube4-pointmicroprobeVTubecross-sectionTubeside-viewIntelligentMicrosystemLaboratoryUniversityofMissouri-Rolla7Experimentalsetupwithaporoustube•FlowsystemandInstrumentation•AcloserlookoftheoxygensensorstripIntelligentMicrosystemLaboratoryUniversityofMissouri-Rolla8SurfacedissolvedoxygenmeasurementwithacommercialClark-typemini-probe•ReflectingO2valueofinnersol.at(+)pressures.•Convergenceto20%value(air-sat.value)at(-)pressures.-10010203040506070-3.0-2.0-1.00.01.02.03.0Internalpressure(kPa)Sensoroutput(O2%)0%solution20%solution50%solution-1001020304050607001020304050O2%innutrientsolutionSensoroutput(O2%)3.0kPa1.5kPa0.5kPa0kPa-0.5kPa-1.5kPa-3.0kPa•PlottedwithrespecttoO2contents.IntelligentMicrosystemLaboratoryUniversityofMissouri-Rolla9Surfacedissolvedoxygenmeasurementwithamicrosensorarray•ReflectingO2valueofinnersol.at(+)pressures.•Scatteringaround0%valueat(-)pressures(duetosurfacedrynessandabsenceofsensorpermeablemembrane).•PlottedwithrespecttoO2contents.-10010203040506070-3.0-2.0-1.00.01.02.03.0Internalpressure(kPa)Sensoroutput(O2%)0%solution20%solution50%solution-1001020304050607001020304050O2%innutrientsolutionSensoroutput(O2%)3.0kPa1.5kPa0.5kPa0kPa-0.5kPa-1.5kPa-3.0kPaIntelligentMicrosystemLaboratoryUniversityofMissouri-Rolla10Surfacewetnessmeasurementwitha4-pointmicroprobearray•Asteepdecreaseofsurfaceimpedanceatthetransitionfrom(-)to(+)pressure.0.05.010.015.020.025.0-3.0-2.0-1.00.01.02.03.0Internalpressure(kPa)Impedance(kOhm)waterfilmDrysurfaceIntelligentMicrosystemLaboratoryUniversityofMissouri-Rolla11On-chipintelligenceofdissolvedoxygenmicrosensorwithbuilt-inmicroactuator;insituself-diagnosis•O2-richorO2-depletedmicroenvironmentsestablishedbywaterelectrolysis.-2H2O4H++4e-+O2(atAEasanode)-2H2O+2e-2OH-+H2(atAEascathode)ConstantcurrentsourceActuatingelectrode(AE)Counter-actuatingelectrode(AE’)MicrosensorSamplesolutionMicroenvironmentIntelligentMicrosystemLaboratoryUniversityofMissouri-Rolla12SensorresponsesduringO2-generatingactuationphaseswithvariouscurrentdensities(inbulksolution)(b)(b)•Responseratio(saturation@t=90/baseline@t=0).•“Excessive”responses(beyond476%,i.e.100%/21%).(a)(a)•ApproachingtoO2-saturationvaluewithincreasingactuationcurrentdensity.IntelligentMicrosystemLaboratoryUniversityofMissouri-Rolla13Whyexcessiveresponse(over476%)?1.Super-saturation;excessivesolubilityofelectrochemicallygenerateddissolvedgasneartheelectrode.2.pHshiftaccompanyingtothegasgeneration;dependenceoftheoxygenreductioncoefficient(catalyticactivity)onsolutionpH.InlowpH(n=4);O2+2H2O+4e-4OH-InhighpH(n=2);O2+2H2O+2e-H2O2+2OH-,H2O2+2e-2OH-IntelligentMicrosystemLaboratoryUniversityofMissouri-Rolla14Whyexcessiveresponse?(continued)3.Pseudo-convection;concentration-drivenconvectionfromtheAEtoenhancethemasstransferofoxygentotheWE.4.Electrochemicalinterference;“feedback”ofH2O2tobeconvertedatAE(H2O22H++O2+2e-,byproductofoxygenreduction@WE).5.Temperature;localtemperatureelevationduetohighcurrentdensityinAE.IntelligentMicrosystemLaboratory