Statesnano5

1SynthesismethodofasymmetricgoldparticlesBong-HyunJun1,MichaelMurata2,EunilHahm1&LukeP.
Lee2Asymmetricparticlescanexhibituniqueproperties.
However,reportedsynthesismethodsforasymmetricparticleshindertheirapplicationbecausethesemethodshavealimitedscaleandlacktheabilitytoaffordparticlesofvariedshapes.
Herein,wereportanovelsyntheticmethodwhichhasthepotentialtoproducelargequantitiesofasymmetricparticles.
Asymmetricrose-shapedgoldparticleswerefabricatedasaproofofconceptexperiment.
First,silicananoparticles(NPs)wereboundtoahydrophobicmicro-sizedpolymercontaining2-chlorotritylchloridelinkers(2-CTCresin).
Then,half-planargoldparticleswithrose-shapedandpolyhedralstructureswerepreparedonthesilicaparticlesonthe2-CTCresin.
Particlesizewascontrolledbytheconcentrationofthegoldsource.
Theasymmetricparticleswereeasilycleavedfromtheresinwithoutaggregation.
WeconfirmedthatgoldwasgrownonthesilicaNPs.
Thisfacilemethodforsynthesizingasymmetricparticleshasgreatpotentialformaterialsscience.
Asymmetricparticleshavedrawnconsiderableattentioninrecentyearsfortheirnovelproperties.
Owingtotheiruniqueintra-particlepotentialforcouplingandlocalfieldenhancement,applicationsincludethefabricationofoptical,optoelectronic,andsensingdevicessuchasfortargetedcellularimagingsystems1–5.
Therefore,thesizeandshapeofparticlesarecriticalfactorsindeterminingtheirmaterialproperties.
Thus,theabilitytocontroltheseparametersthroughoutthesynthesisprocesshasbecomeamajorgoalinthefieldofmaterialsscience6–12.
Sofar,synthesistechniqueshavebeenreportedforafewotherlowsymmetrymetalparticlesincludingnano-rodsandnano-clusters,butresearchintothescale-upfabricationofasymmetricparticlescanbefurtherdevelopedinsomestructures13.
Thesesynthesismethodsutilizekineticcontrolovernucleationofthenano-clusterthroughacarefullydeterminedpolymerconcentrationforstericstabilization,whichlimitstheirabilitytoscaleupduetoaggregation.
E-beammethodscombinedwith2-Dplatewerereported4,5,14.
However,thesemethodsonlyuseasmallareaduetothelimitationofthee-beammethodand2-Dplatesize,quantitiesofparticlescanbehighlylim-ited.
Afacileandwidelyapplicablemethodforsynthesizingavarietyofasymmetricparticlesinlargequantitieswouldhelpexploittheirpotentialandpavethewayforanewfieldinasymmetric-particle-basedscience.
Herein,wereportanovelmethodforthepreparationofvariousasymmetricparticles.
Inourapproach,micro-sizedsphericalbeadswereusedascapturetemplatesfornano-sizedsilicaspheres.
Then,asymmetricgoldparticlesweregrownonthenanometersilicaspheres.
Differentsizeandshapeofgoldparticlescouldbegrownbychangingtheconcentrationofthemetalsourceandthetypeofsolvent.
Thegoldstructurescanbeobtainedasparticles.
ResultsandDiscussionThefabricationmethodforasymmetricparticlesisillustratedinFig.
1.
Twotypesofbackboneswereused:amicro-sized(72–150m)immobilizedsphericalpolymerwith2-chloritylchloridelinkers(2-CTCresin)andnano-sizedsilicaspheres(120nm,seesupportingFig.
1).
2-CTCresinsarewidelyusedforsolid-phasepeptidesynthesis.
Theirkeyadvantagesarelowercostandrecyclability15–17.
The2-CTCresinscanformacovalentbondwithnucleophilicfunctionalgroupssuchasthi-ols16,amines18,andcarboxyls19.
Thisbondcanbecleavedeasilyundermildlyacidicconditions.
(seesupportingFig.
2)Toimmobilizesilicananoparticles(NPs)ontothe2-CTCresin,thiol-functionalized90nmsilicaNPswereprepared20andmixedwith2-CTCresinunderbasicconditions.
Here,weuseddimethylsulfoxide(DMSO)asthesolvent,whichisaproticandpolar.
Becauseproticsolventscancompetewiththenucleophilicsubstitutionreactionofthe2-CTCgroup,anaproticsolventwasused.
Amongaproticsolvents,polarsolventsarecompatiblewiththehydrophilicfunctionalizedsilicaNPsandincompatiblewiththehydrophobicresin,causingshrinkage1DepartmentofBioscienceandBiotechnology,KonkukUniversity,Seoul,143-701,RepublicofKorea.
2DepartmentofBioengineering,BiomolecularNanotechnologyCenter,BerkeleySensorandActuatorCenter,UniversityofCalifornia,Berkeley,California,94720,UnitedStates.
CorrespondenceandrequestsformaterialsshouldbeaddressedtoB.
-H.
J.
(email:bjun@konkuk.
ac.
kr)orL.
P.
L.
(email:lplee@berkeley.
edu)Received:4December2015Accepted:12April2017Published:xxxxxxxxOPEN2oftheresinandpreventingthetrappingofNPsinsidetheresin.
Afterthereaction,theremainingsilicaNPsandexcessreagentsandsolventswereremovedfromthesilicaNPimmobilizedresinbyfiltrationandwashedwithethanol.
ThesilicaNPsimmobilizedonthe2-CTCresinwereanalyzedbyscanningelectronmicroscopy(SEM).
SilicaNPsweresuccessfullyimmobilizedontothesurfaceof2-CTCresin(seesupportingFig.
3b).
VarioussilicaNPssuchasamine-functionalizedNPs(50and120nm)andthiol-functionalizedNPs(200nm)werealsoimmo-bilized(seesupportingFig.
3c–e).
ThesilicaNPloadingamountscanbecontrolledbytuningtheirconcentration(Datanotshown).
Thegoldsource(1%w/winDIwater)andreductant(hydroxylamine,0.
5mg/mLinwater)werethenaddedforpreparingasymmetricparticles.
Oneexclusiveadvantageofourmethodcomesfromcombiningahydropho-bicresinwithhydrophilicsilicaNPs.
BecausehydrophilicgoldsourcesinH2Opreferhydrophilicsurfacesratherthanhydrophobicsurfaces,goldisabletogrowonthesilicaNPsundercertainconditions,asshowninFig.
2a.
Moreover,thesilicaNPsformstrongcovalentbondswiththebeads,permittingtheapplicationofvariouscondi-tionswithoutconcernforstability.
Here,wealteredthegoldionconcentrationandsolvent.
Asaresult,wecouldsynthesizegoldNPswitharoseorpolyhedralshapeonthebeadsasshowninFig.
2b.
(seesupportingFig.
4)Whentheconcentrationofgoldwasincreased,theaveragesizeoftheparticlesalsoincreased,asshowninFig.
2c(seesupportingFig.
5).
Generally,particlesaggregatewithoutchargerepulsionorspacerstoreducesurfaceenergyinthesynthesisstep.
Thisisoneofthemostcriticalconsiderationsinthesynthesisofcolloidalparticles,asshowninsupportingFig.
6.
BecausethesilicaNPswerephysicallyseparatedfromeachotherinourmethod,theparticleswhichhavegapbetweenparticlesdidnotaggregateduringthegoldgrowthstep.
(seesupportingFig.
7)Moreover,targetNPswereimmobilizedonthelargermicro-sizedresinsuchthatevenifnucleationweretohappen,thenucleatedNPscouldeasilyberemovedfromlargermicro-sizedresinbyfiltration.
Thus,nucleationofgoldinsolutionwasnotaconcern.
Theseadvantagesenabledustoapplyavarietyofconditionsforgoldgrowth.
AmongthevariousshapesshowninFig.
2b,therose-shapedparticleonthebeads(Fig.
2bi)wasthemodelforthisstudy.
Beforetheparticleswerecleavedfromthebeads,mercaptopropionicacid,whichhasathiolgroupononesideandacarboxylicgroupontheotherside,wasaddedtogeneratechargerepulsionandpreventaggregation.
Toobtainthesynthesizedparticlesfromtheresin,thebondswerecleavedusingmildlyacidicconditions,1–2%trifluoroaceticacid(TFA)inmethylenechlorideinseparatereactionvessels(i.
e.
,aLibratubewithafilter).
Thiscleavagestepisawell-knownchemicalreaction20,21thatresultsinthe2-CTCgroupsremainingontheresin(>72m)andamixturecontainingtheasymmetricNPs(Nano5,6774–6778,doi:10.
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Figure3.
GoldNPsofvariousshapesandsizesimmobilizedonthebeads.
(a)IllustrationofgoldgrowthonthesilicaNPs.
(b)SEMimagesofgoldcoatedsilicaNPsonthebeads(200M)(i)inH2Osolvent(stirring),(ii)inH2Osolvent(shaking)(iii)inEtOHsolvent,(c)SEMimagesofgoldcoatedsilicaNPsonthebeads(inH2Osolvent)(i)50M,(ii)200M,(iii)800M.
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AcknowledgementsThisworkwassupportedbyKonkukUniversityin2016.
AuthorContributionsInthismanuscript,Bong-HyunJunandLuke.
P.
Leeconceivedanddesignedtheexperiments.
Bong-HyunJunandMichaelMurata,EunilHahmperformedtheexperimentsandanalyzedthedata.
Bong-HyunJun,MichaelMurata,andLukeP.
Leewrotethemanuscript.
AdditionalInformationSupplementaryinformationaccompaniesthispaperatdoi:10.
1038/s41598-017-02485-7ChangeHistory:AcorrectiontothisarticlehasbeenpublishedandislinkedfromtheHTMLversionofthispaper.
Theerrorhasnotbeenfixedinthepaper.
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