Nanoparticle roleon the repeatabilityof stimuli-responsivenanocomposites
Sungsook Ahn1,2andSangJoonLee1,2,*
1BiofluidandBiomimic Research Center, 2Department of MechanicalEngineeringPohangUniversityof ScienceandTechnology,Pohang, 790-784, Korea.
*Correspondence
Tel:+82-54-279-2169,Fax: +82-54-279- 3199, E-mail:
SupportingInformation
PreparationofsphericalAuNPsof20nminaveragediameter.Topreparegoldnanoparticles(AuNPs),goldchloride(III)trihydrate(HAuCl43H2O)isdissolvedinDIMilli-Qwater(1.010-3mol/L)underrefluxing.SodiumcitratetribasicdihydratesolutioninDIwater(410-2mol/L)isaddedtotheabovesolution.Reactioncompletionisdetectedbycolorchangesfrompaleyellowtowinered.Boilingconditionisfurthermaintainedfor15minafterthecolorchangeiscompletedandthencooledtoroomtemperature.TheAuNPsolutionisdialyzedovernightusingSpectra/Por7membrane(1,000Dacut)againstDIMilli-Qwatertoremoveexcesssodiumcitratetribasicdihydrate.TheAuNPsolutionsareplacedonatypicalcoppergridandthendriedunderairatroomtemperaturefortransmissionelectronmicroscopy(TEM)(JEOLCs-correctedHR-TEM,JEM-2200FS).GiventhattheorganiclayersoftheAuNPsarenotclearlydetectedbytheelectronbeaminTEM,goldcoreswithhighelectrondensityineachAuNPsarecaptureddistinctively.FromthisTEMimage,the average diameter ofthe formedAuNPs is adjusted to beapproximately20 nm.
PreparationofinterconnectedAuNPsbyPEGs.Thiolend-cappedpolyethyleneglycol(PEG)ligandsareaddedatthesecondstep.Bi-functionalandfour-armedPEGsarepurchased(LaysanBio,Arab,AL,USA)andusedwithoutfurtherpurification.AfterthesizeoftheAuNPisdeterminedby theaforementionedmethod,designedamountofligandaqueoussolutionisaddedtotheaboveaqueoussolutiontomodifythesurfacepropertiesofthecitrate-coveredAuNPandstirredatroomtemperatureorhigher(between50Cand60
C)for6hto12huntilnofurthercolorchangeisobserved.Theun-reactedresidueligandsareminimizedtobelessthan1ppmbytestingaliquotofthesamples.TheAuNPsolutionsaredialyzedovernightbySpectra/Por7membrane(25KDacut)againstMilli-Qwaterforpurification.Theaqueoussurface-modifiedAuNPstocksolutionsareadjustedtohaveaconcentrationofabout2.41018AuNPs/m3inconsiderationofthediameterofAuNPs(average20nmindiameter)andtheHAuCl4concentrationof1.010-3mol/L.GiventhatthestandardconcentrationoftheAuNPstocksolutionof1.0mmol/L,theconcentrationofthe ligandstock solutionis controlled to 10 mmol,50 mmol and 100 mmol(Figure S2).
ThephysicalpropertyoftheAuNPclustersformedbyPEGinter-linkingisinvestigatedbyUV-visspectrum.PhysicallyhybridNPclusterstypicallyred-shift(suchasnaturalaging).TheUV-visspectraofdesignedAuNPstetheredby aconstantPEGchainlength10000butindifferentlinear-,binary-,andquaternarystructuresarecompared(FigureS1a).TheAuNPslinkedbylinear PEGgenerate surface plasmonatapproximately=540 nm, which is similartothatofthesingleAuNPof20nmdiameter.However,theAuNPslinkedbybinaryandquaternaryPEGsshiftto=610nmand=630nm,respectively.TheUV-visspectrumofthedesignedPEG-AuNPnanocompositeclustersclosely resemblesthatofphysicalNPaggregation.Inaddition,the4PEG-linkedclustersred-shiftmoreeffectivelythan2PEG-linkedones.Characteristiclight-responsivenessofAuNPclusterschangesaccordingtothestructure oftheinterlinkingmolecules.
NPsaretypicallyconsideredtoperformarandomwalkonthelatticemodel.Inaddition,effectiveparticlemobility onthelatticeiscontrolledbyspecificparticle-to-solventstepratios.ThelatticemodelillustratedinFigureS1bisadoptedtodescribetheinter-linkedAuNPPEGcompositeclusters.EachlatticecontainsoneAuNP,andtheselatticesarediversely interconnected according to the molecular weight and structure of the PEGs.
MultiplePEGlinkagesareattachedtothesurfaceoftheAuNPstoformassemblies.Mono-tetheredAuNPsareanalogoustosingle-tailedsurfactantsordiblockcopolymers,whereasmulti-tetheredAuNPsworkasjunctionpointsinthepolymernetwork.Theyalsopossessadditionallevelsofcomplexityandanisotropythatcanbeexploitedinself-assembly.Thecrosslinkdensity()ofthefully-interlinkednetworkisinverselyproportionaltotheMwbetweenjunction points (Mp).
FigureS1.(a)UV-visspectroscopyoftheAuNPsof20nmindiameterlinkedbyPEGsofdifferentstructurebutthesamearmlengthof10000.TheAuNPslinkedbyalinearPEG10000exhibitsUV-visabsorbanceat540nm,whilethoselinkedbybinaryandquaternary2PEG10000and4PEG10000havefarlongerwavelengthof610and630nm,respectively.
(b)LatticemodeltodescribethestructuresoftheAuNP-PEGnanocompositenetworks.EachAuNPlocatesinalatticeandPEGsinterconnectthoseAuNPs.(c)VariationoftheclustersizeoftheAuNPslinkedby2PEG3400,2PEG10000,4PEG10000and4PEG20000withtheconcentrationof10,50,100(numberofPEGs/numberofAuNPs).Theclustersizeisaveragedfrom100clustersoftheXNIimages.NumbersonthegraphmeansPEGconcentrationfor each case. The standard deviation is markedaslight bluebar foreachcase.
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FigureS2.AuNPandPEGratioeffectobtainedbySAXS.Theaqueoussurface-modifiedAuNPstocksolutionsareadjustedtohaveaconcentrationofabout2.41018AuNPs/m3.GiventhatthestandardconcentrationoftheAuNPstocksolutionof1.0mmol/L,theconcentrationofthePEGligandstocksolutioniscontrolledto10mmol(10),50mmol(50)and100mmol(100).(a)2PEG3400(b)2PEG10000,(c)4PEG10000and(d)4PEG
20000.Beyondthecriticalq*valuethesystemsareresponsivetothetemperature.However,belowthatq*valueallthesystemsarestable.Theq*valuesmovetothehigherqregionwithincreasedPEGamountforallsystems,indicatingsmallersizeregionfromwhichrespondingto the external stimuli.
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Small-angleX-rayscattering(SAXS).SAXSmeasurementsareperformedatthe4CsynchrotronSAXSbeamlineofPAL.Samplesof1mmthicknessareusedbystackingfiveSiwafersampleholdershaving200m-thickSiN3windowatthecenter.Thesample-to-detectordistanceisfixedat3m,coveringtheqrangeof0.04nm-1q0.75nm-1,whereq
=(4π/λ)sin(θ/2)isthemagnitudeofthescatteringvectorandθisthescatteringangle.TheqrangeiscalibratedusingSEBS[polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene].ThecollectedSAXSdataarecorrectedbysubtractingthedataofbackgroundandemptycellscattering.Allmeasurementsareperformedattheisothermalconditionof20°C.ThedesignatedqrangeisfocusedonthepolymericnetworkedstructuresofPEGs,notonthesizeoftheAuNP.Therefore,theqregiondisplayedinthisstudy doesnotoverlapwiththoseoftheAuNPs(ifthereisnospecificmention);hence,thepeakcomespurelyfromthepolymericnetworkclusterstructures.TheresultsofthehigherqrangementionedinthisstudywhichcorrespondstotheAuNPs,arenotpresented.Instead,thesizeoftheAuNPsisdiscussedbased on theTEM results.
FigureS3. Experimentalset-upfor smallangle X-rayscattering(SAXS) atPAL
SynchrotronX-raynanoscopy(XN).Experimentsarecarriedoutatthe7CbeamlineofPAL.TheX-raysourceof1011(photons/m2/sec)isconsistedofanundulatorwith20mmperiodand70poles.Thebeamsizeis100m100mat7keV.TheX-ray beamsourceis radiatedfroma3 GeVbendingmagnetandthenmonochromatizedusingaGe(111)DCM.Forfocusedimages,monochromaticX-raybeamofnominallyselected7keVisfocusedonthesampleusingacondenserzone-plate(CZP,Berylliumrefractivecompoundlensesof1mmdiameter)withinnermostandoutermostdiametersof4nmand100nm,respectively.Astainlesssteelannularringaperture(AA)with2.4mminnerand3.2mmouterdiametersisusedtoobtainahollow-conetypeX-rayilluminatesonasamplenecessaryfortheZernikephase-contrastimaging.An ordersorting aperturemade of a tungsten plateis used not onlytopassthefocusedbeambutalsotoblockthe0thandhigherorderdiffractedX-rays.Animagingzone-plateisfabricatedwith1.6µm-thickgoldringsonasiliconnitride(Si3N4)membrane of 100nmthickness.Thedepthof focusoftheobjectivezoneplateis200µmat7keV,forwhichthepracticalsamplethicknessislimitedtolessthan200µm.Forthephase- contrastimaging,agoldplatedring-shapedphaseplate(PP)arrayislocatedatthedownstreamoftheobjectivelens,andtheringdimensions(114.6µm)arematchedwiththatoftheAAlocatedattheCZP.Foranexperimentalset-upoflargefiled-of-view,CZPisremovedtogetthedivergedbeamonthesample.ThethicknessofthePPisabout0.7µm,whichcorrespondstothe/4phasedelayforpositivephasecontrast.TheprimaryX-rayimageismagnified50timesusing anobjectivezoneplatelens(140minnermostand50nmoutermostdiameter,W)andisconvertedintoavisibleimageonathinscintillatorcrystal(Tb:LSO,20mthickness).Thevisibleimageisfurthermagnified20,usinganopticalmicroscope,providingatotalmagnificationof×1000imageonacooledCCDcamera(PrincetonInstrumentVersArray1300BcooledCCD)of1340pixel1300pixelresolution, whichcorrespondstoanequivalentfieldofviewof21µm21µminphysicalsize.Silicon(Si)waferholderhassiliconnitride(SiN3)membranewindowatthecenterisusedasasample holder.The figure is created by the authors.
FigureS4. Experimentalset-upfor X-raynanoscopy(XN) atPAL
Two-dimensional(2D)X-raymicroscopy(XM).SynchrotronX-rayimagesarecapturedat6D beam lineofthePohangAcceleratorLaboratory(Pohang,Korea).TheX-raysourcewasabendingmagnetwithacriticalenergyof8.7keVat3GeVelectronenergyoperation.Thewhitebeamwasattenuatedbyapolishedberyllium(Be)of0.5mmthicknessorpolishedSiwaferof1mmthickness.Thephotonenergy(E)wasabout22keVwithenergyresolution(ΔE/E)of15.8keVto34.4keV(~84%).Thebrightnesswas221012(ph/s/mm2)andthebeamsizewasabout30mm(H)5mm(V).Thesampleswereplacedatapproximately30mdownstreamofthesource,whereasthedetectorwasplaceddownstreamoftheobjectsat30cm.ThesizeoftheX-raybeamilluminatingthetestsamplewasadjustedtothatofthefield-of-viewusing aslitmoduletoavoidunnecessaryexposureofX-raybeamonthesample.Anattenuatormadeofaluminum(Al)sheetswaslocatedatthebeaminletoftheexperimenthutchonthewayofX-raypropagationpathwaytoattenuatelightintensity,evenwhennoimagewasphotographed.ThisattenuationoflightintensityprotectedthesampleanddetectorfromstrongX-rayirradiation.TheprimaryX-rayimagewasconvertedintoavisibleimageonathinscintillatorcrystalCdWO4of100mthickness.X-rayimageswerecapturedusingaCCDcamera(PCO,PCO2000).Thefield-of-viewwitha10objectivelensattachedinfrontofthecamerawasapproximately3.6mm2.4mminphysicaldimension.Thepixelsize wasabout 0.9m.
FigureS5. Experimentalset-upfor X-raymicroscopy(XM) atPAL.
PyreneorRhodaminetransportthroughAuNP-PEGcompositesinaqueoussolution.Rhodamine6Gisanionicmoleculeofhighwatersolubilityexhibitingdarkorangecolorinwaterandoftenusedasatracertotracktherateanddirectionofflowinwater.Ontheotherhand,Pyreneisanonionichydrophobicmoleculesandissensitivetothefluorescencedetection.AstocksolutionofPyrene(watersolubility:0.135mg/L)ispreparedbyaddingaknownweightofthecompoundin20wt%ethanolinwater.Themixtureissonicatedtoyieldaclearsolution.Theexperimental2μMsolutionofPyreneispreparedfromitbydilutionwhereintheethanolconcentrationis0.5%.Suchasmallconcentrationoftheethanolisconsiderednottoaffectthestimuli-responsivenessofAuNP-PEGnanocomposites.Withhighwatersolubility(400g/L),Rhodamine6Gisdirectlydissolvedin waterandusedas asaturatedsolution.AuNP-PEGcompositessolutionsareloadedinaSpectra/Por7membranebag(1000Dacut)andputinatemperature-controlledtubeasshowninFig.4a.ThevolumeandtheheightoftheAuNP-PEGcompositeembeddedPVAmatrix(Mw~72,000Merck,3wt%)iscarefullydesigned.Pyrenedissolvedsolution3mLisloadontopofthetowerandthenaliquotsamplesarecollectedateveryminute.Aseriesofcollectedsamplesaremeasuredbyfluorescencespectrawhicharerecordedusingaspectrophotometer.APerkinElmerLuminescenceSpectrometerL550BSystemwithFLWinlab4.0softwareisusedtoobtainallfluorescenceexcitationandemissionspectra.SolutionsareheldinAgilentTechnologiesOpen-topUVQuartzCells(10mmby 10mm)with3.0mLofvolume.Spectraareobtainedwithascanrateof100nm/sandintensitiesarecollectedat0.5nmintervals.Anemissionwavelengthof428nm,anexcitationwavelengthof326nm,andslitwidthsof2.50nmforbothemissionandexcitationareusedforPyrenespectra.Pyreneshowssignificantabsorbanceatthiswavelengthhenceitsuseasanexcitationwavelength.ForRhodamine6Gspectra,anexcitationwavelengthof485nm,anexcitationslitwidthof10nm,andanemissionslitwidthof2.50nmareused.Allspectraareobtainedat25C.IntermsofthetnofPyreneand Rhodamine, hydrophobicPyreneshowslongertn comparedwiththat ofhydrophilic Rhodamine showingeffective water tracking.
FigureS6.(a)Clustersize(IandII)andporesizeinacluster(IIIandIV)areconsidered.(b)Clustersizevs.retentiontime(tn),(c)Temperaturevs.tnand(d)1/qvstneffectonthetransportoftwodyes(PyreneandRhodamine6G)througheachdesignedPEGlinkedAuNPclusters.The appliedflow is controlledbygravity.
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