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MultipleandHigh-ThroughputDropletReactionsviaCombinationofMicrosamplingTechniqueandMicrofluidicChipMembers:李娜冯双霞徐秋燕刘婷婷聂怀军ContentsBackgroundExperimentABSTRACTDiscussionABSTRACTMicrodropletsofferuniquepartmentsforacmodatingalargenumberofchemicalandbiologicalreactionsintinyvolumewithprecisecontrol.Amajorconcernindroplet-basedmicrofluidicsisthedifficultytoaddressdropletsindividuallyandachievehighthroughputatthesametime.Here,wehavebinedanimprovedcartridgesamplingtechniquewithamicrofluidicchiptoperformdropletscreeningsandaggressivereactionwithreagentconsumption.Ourbineddeviceprovidesasimplemodeltoutilizemultipledropletsforvariousreactionswithlowreagentconsumptionandhighthroughput.BackgroundAlargenumberofreactionscanbeindependentlyminiaturizedintotinydropletsrangingfromnanolitertopicolitersizeswithouthavingtoincreasethechipsizeandplexity.Microfluidicchipshaveprovidedapowerfulplatformforacplishingdropletformationandmanipulationwithinonechipofonlyafewsquarecentimetersinsize.AdvantagesOverthepastfewyears,droplet-basedmicrofluidicshasattractedincreasingattention.Background

Dropletgenerationformultiplesamplesislimitedbythe“world-to-chip”interfaceproblemandcannotbeaddressedindividuallyDropletgenerationandmanipulationfunctionswithinonechipcaneasilyinterferewitheachotherandaredifficultTobalance,despitebeingseparatedbyalong,windingchannel.DrawbackPassivedropletformationmethods:InnovateThiscontextshowsahybriddevice:thecartridgedropletgenerationtechniquebinedwithamicrofluidicchip.Theyimprovedthecartridgetechniquewithanovelmovementscheme:thecapillary,insteadofthemultiwellplate,wasmovedbyadigitalandautomaticmanipulatortoaspiratedifferentsamplesorthecoveringoil.Thehybriddropletdeviceforgenerationandmanipulationconsistsoffourmajorponents.(a)manipulator(b)multiwellplate(c)capillary(d)PDMSchipThreegeneralsteps

loadthemultiwellplatewithdifferentsamples,coverwithalayerofoil,andinputtheparametersofthedesireddropletarrayintothecontrollerviaaPC

startthecontrollertoaspiratecertainvolumesofsamplesandoilintotheCapillarysequentially

introducethegenerateddropletsintothePDMSchipformerging,mixing,detection,orothermanipulation.Laboratoryreagent

siliconeoil,

FeCl2·4H2O(Sigma−Aldrich),FeCl3·6H2O(AcrosOrganics),ammoniumhydroxidesolution(28%NH3Fluka),andhydrochloricacid(37%HCl,AcrosOrganics)ImprovedSamplingTechnique

CombinedDropletDevicePerformance

High-ThroughputDropletScreening

AggressiveDropletReaction

ImprovedSamplingTechniqueThecapillaryaspiratestheoilwhenthecantileverremainsinthe“up”state.Whenthecantileveristriggeredtostayinthe“down”state,thecapillaryaspiratesthesample.Theresidencetimeintheoil(TO)andsample(TS)couldbeadjustedrespectivelytogeneratedropletswithdesireddistanceandvolume.(c)Relativeintensitywasmeasuredalongthechannelstartingfromtoprightcorner.TheintensityoffluoresceinandDIwaterdropletdoesnotdecreaseorincrease,whichindicatesthatnocross-contaminationbetweenthesetwosampleswasdetected.(b)Dropletarraywasgeneratedbysequentiallyaspirating50uMfluoresceinandDIwater.CombinedDropletDevicePerformanceHere,themergingofdropletswasdemonstratedinaPDMSchip.ThedropletsfusiondoesnotdependondropletdistancebutdropletvelocityandVd/Vc.Aftermixingpletely,themergeddropletwasoutputtoasinuouschannelfordisplayanddetection.Inthefirstapplication,aseriesofAiandBm,n(i=1−2,m=1−3,andn=1−6)weregenerated.A1andA2areFluo-4andRhod-2solutionswiththesameconcentration(10.8μM),whichareindicatorsthatexhibitanincreaseinfluorescence(green/red)uponmetalionbonding.Avalueofm=1−3representmetalsionsolutionsofLaIII,YbIII,andYIII,respectively,whilen=1−6aresixdifferentmetalionconcentrations(0,2.5,5,10,20,and40μM)ofthesesolutions.Thedropletarraycontains721-nLdropletsHigh-ThroughputDropletScreeningThe36pairsofdropletreactionsused∼72nLofsolutionandrequired1.8mintoplete.Therefore,thereagentconsumptionforeachmeasurementcouldbereducedto1nLpersample,andthereactionthroughputis1200h−1,whichcanbemuchfasterbyincreasingtheflowvelocity.ThescreeningdropletscouldbestoredinthePDMSchipafterwestoppedthevacuum.AggressiveDropletReactionFromtheseimages,wefoundthatthecoprecipitationissofastthatitimmediatelyformsparticleswhentwodropletseintocontactwitheachother.Moreover,ineachvolumeratio,theprecipitationinitiatedbythefusionoftwodropletsdidnotblockthemicrochannelatsuchhighconcentrations.Suchflexible,controllableandminiaturizedreactionconditionsareextremelysuitableforaggressive,fast,orevenexplosivereactionsthatgenerateprecipitationorheat.DiscussionThecartridgedropletgenerationmethodprovidesanefficientwayforintroducingdifferentnanoliterdropletsintothemicrofluidicchip.themicrofluidicchipoffersaplatformfordelicatemanipulationsuchasmerging.Thisfeatureisvaluableforreducingthereactionscreeningandoptimizationcostandtimeandisparticularlyusefulfordrugscreening.Comparedwiththeothercartridgedropletgeneration,ourdesignusedadigitalandautomaticmanipulatortomovethecapillaryinsteadofthemultiwellplate.Dis