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Biomolecule-assistedsynthesisofhighlystabledispersionsofwater-solublecoppernanoparticles

JingXiong,Xue-dongWu ,Qun-jiXue

NingboInstituteofMaterialsTechnology&Engineering,ChineseAcademyofSciences,Ningbo315201,China

articleinfoabstract

Water-solubleandhighlystabledispersionsofcoppernanoparticleswereobtainedusingabiomolecule-assistedsyntheticmethod.Dopaminewasutilizedasbothreducingandcappingagentinaqueousmed-ium.ThesuccessfulformationofDA-stabilizedcopperparticleswasdemonstratedbyultraviolet–visiblespectroscopy(UV–Vis),transmissionelectronmicroscopy(TEM),Zetapotentialmeasurement,andFou-riertransforminfraredspectroscopy(FT-IR).Themechanismofdopamineontheeffectivereductionandexcellentstabilityofcoppernanoparticleswasalsodiscussed.Thisfacilebiomolecule-assistedtech-niquemayprovideausefultooltosynthesizeothernanoparticlesthathavepotentialapplicationinbiotechnology.

Ó2012ElsevierInc.Allrightsreserved.

Articlehistory:

Received16June2012

Accepted14September2012

Availableonline26September2012Keywords:

Biomolecule-assistedBiomoleculesDopamine

CoppernanoparticlesWater-soluble

1.Introduction

Overthepastdecade,metalnanoparticleshaveattractedmuchattentionintheemergingareasofnanoscienceandengineeringtechnologyduetotheirunusualchemicalandphysicalproperties,suchascatalyticactivity,novelelectronic,optic,andmagneticproperties[1–6].Someofthemostpromisingapplicationsformetalnanoparticlesincludecatalysts,absorbents,chemicalandbiologicalsensors,optoelectronics,informationstorage,aswellasphotonicandelectronicdevices[7–10].Variousmethods,suchaswetchemicalreduction,reversemicelles,electrochemicalandsonoelectrochemicaltechniques[11–16],weredevelopedtosyn-thesizemetalnanoparticlesbecauseofthediversityandimpor-tanceoftheseapplications.However,mostofthesemethodsreportedtodaterelyheavilyonuseoforganicsolventandtoxicreducingagents,formationofenvironmentalandbiologicalhaz-ardousby-products,andhighenergyconsumption.Thepotentialapplicationareaswerecontainedowingtotheseproblems.

Recently,thereisanincreasingattractiononthetopicofsyn-thesizingmetalnanoparticleswithbiomoleculessuchasDNA,aminoacidandproteintoreduceoreliminatetheuseandgenera-tionofhazardoussubstances[17–20].Biomolecules,whicharethebuildingblocksoflifeandperformimportantfunctionsinliving

Abbreviations:CuNPs,coppernanoparticles;DA,dopamine;UV–Vis,ultraviolet–visiblespectroscopy;HRTEM,high-resolutiontransmissionelectronmicroscopy;FT-IR,Fouriertransforminfrared.

Correspondingauthor.Fax:+8657486685159.

E-mailaddresses:xiongjing@http://wendang.chazidian.com(J.Xiong),xdwu@http://wendang.chazidian.com(X.-d.Wu).

0021-9797/$-seefrontmatterÓ2012ElsevierInc.Allrightsreserved.http://wendang.chazidian.com/10.1016/j.jcis.2012.09.030

organisms,havebeenusedtodesignandsynthesizecomplicatednanostructuresatmolecularlevel[21].Thepopularityofmetalnanoparticleshasbeenenhancedthroughextendingitsapplicabil-ity,especiallyinbiologicalapplications,bytheintroductionofbio-molecules[22,23].Therefore,severalsyntheticmethodsrelyingonbiomolecule-assistedtechniquehavesofarbeenreported,espe-ciallyfornoblemetalnanoparticlessuchasAuandAgnanoparti-cles.Dharetal.[24]synthesizedandstabilizedAunanoparticlesbyusinggellangum(alinear,anionicheteropolysaccharide)inwater.Sietal.[25]preparedAuandAgnanoparticlesusingoligo-peptidesasboththereducingandstabilizingagent.Burtetal.[26]fabricatedAunanoparticlesthroughdirectlyconjugatedtobovineserumalbuminproteinbychemicalreductioninaqueoussolution.Lietal.[27]synthesizedfolicacid(FA)-protectedAunanoparticlesbyheatinganaqueoussolutionofHAuCl4/FAinwhichFAactsasboththereducingandstabilizingagent.

Nevertheless,therearefewstudiesonpreparationofcoppernanoparticles(CuNPs)withbiomoleculesespeciallyinanaqueoussolutionmedium.CuNPsalsoplayacrucialroleinmanyapplica-tionssuchaslubricants,catalysts,thermaltransfernano uids,electronicmaterials,andopticaldevices[28–http://wendang.chazidian.comparedtonoblemetals,copperissigni cantlylowcostandlesselectromi-grationeffectwhenitisusedinmicroelectronics.Apartfromthis,stabledispersionofwater-solubleCuNPssynthesizedbybiomole-cule-assistedmethodnotonlycanbeusedas‘‘ink’’tomanufacturelow-costelectroniccomponentsbyink-jetprinting[31–33]andfabricateorderedmicro/nanostructuredarraysthroughself-assembly[34,35],butalsocanbewidelyusedforbiologicalapplications[36,37].

42J.Xiongetal./JournalofColloidandInterfaceScience390(2013)41–46

Inthiswork,afacilebiomolecule-assistedsyntheticstrategyforpreparinghighlystabledispersionsofwater-solubleCuNPsisreported.Dopamine(DA),akindofbioactiveo-hydroquinonederivativeswitheffectivereduction,isusedasbothreducingandcappingagenttoobtainaswellaspreventtheaggregationofCuNPs.Nootherintermediatestabilizingagents,whichwilladverselyaffecttheperformanceofproductsasorganicresidues,isadded.Transmissionelectronmicroscopy(TEM)wasusedtocharacterizetheshapeandsizedistributionoftheproducedCuNPs.Fouriertransforminfraredspectroscopy(FT-IR)wasemployedtocon rmtheimmobilizationofDAonCuNPs.Further-more,themechanismofdopamineonthereductionandstabiliza-tionofCuNPswasdiscussed.

2.Experimental2.1.Materials

CuCl2Á2H2O(SinopharmChemicalReagentCo.,Ltd.)actedastheprecursorfortheformationofCunanoparticles.Dopamine(AladdinReagentCo.,Ltd.)actedbothasreducingagentandcap-pingagent.Allchemicalswereusedasreceivedanddeionizedwaterwasusedinallexperiments.2.2.SynthesisofCuNPswithDA

Inatypicalpreparationprocess,dopamine

waspreparedbydissolvingdopamine(3mmol)water.A askcontainingDAaqueoussolutioninoilbathwithmagneticstirring.A10mlsolution(1mmol)wasaddeddropwiseintotheThemixturewaskeptat80°CuntiladarkThereactionprocesswaslastabout6h.Thewascentrifugedat8000rpmfor15minandthenambientconditionsfor6months.Followingthewerealsopreparedbyvariousmolarratioof(1:1,2:1)andconcentrationofcoppersaltthesamemethoddescribedabove.

Controlexperimentsrevealedthatthedistributionandstabilitywereallachievedati edabove.Thedependenceofparticlesizeoncoppersaltandconcentrationofcoppersalthasindetail.

2.3.Characterization

TheUV–VisabsorptionspectraofthewererecordedonaLambda950USA).

Samplesforhigh-resolutiontransmission(HRTEM)analysiswerepreparedbydropCuNPsdispersionsoncarboncoatedcopperdryatroomtemperature.MeasurementswereF20(USA)instrumentoperatedatan200kVwithalatticeresolutionof0.14nmandtionof0.24nm.TheparticlesizeanalysiswasNanoMeasurersoftware.

ThestabilityoftheCuNPswasdeterminedzetapotential,determinedbyusingazetaZS,BrookhavenInstrumentsCorporation,NY.

Fouriertransforminfrared(FT-IR)spectraofas-preparedCuNPswererecordedonaFourierspectrophotometer(Nicolet6700,USA)ataintherangeof400–4000cmÀ1inKBrpellets.

3.Resultsanddiscussion3.1.UV/VisstudiesonCuNPs

Nanosizedparticlesexhibituniqueopticalpropertieswithanexponential-decayMiescatteringpro lewithdecreasingphotonenergy.Sometransition-metalnanoparticlesalsoshowadistinctsurface-plasmonband[38].UV–Visabsorbancespectroscopyhasbeenprovedtobeaveryusefultechniqueformetalnanoparticlestudybecausethepeakpositionsandshapesaresensitivetoparti-clesize.TheeffectofcoppersaltandDAconcentrationontheUV–VisabsorbancespectroscopyofCuNPssynthesizedisshowninFig.1.Thesurface-plasmonresonancepeakofCuNPshasbeenreportedtobeappearedaround570nm.However,forcoppernanoparticlesbelow4nmindiameter,thisplasmonpeakdisap-pearsduetothechangeinelectronicstructurethatoccurswithquantumcon nement[39–41].

Inourwork,theUV–Visabsorptionspectrumofbiomolecules-stabilizedCuNPsonlydemonstratesafeaturelessMiescatteringpro lewithouttheappearanceofanapparentsurface-plasmonband,asshowninFig.1,whichqualitativelyindicatesthepresenceofverysmallseparatedcoppernanoparticles(averageparticlesizelessthan4nm),asthesurface-plasmonpeakisknowntobebroad-

3:1)whentheconcentrationof

presentedinFig.2.

Ingeneral,theCuNPsarehomogeneouslydistributed.waslessthan4nm.TheHRTEMlatticefringeswithd-spacinglatticeplanesofmetallictributionarealsopresentedincatehighdegreeofhistogramsclearlyrevealatheincreaseinmolarratioofwithvariousmolarratioof2.34±0.47nm,2.09±0.50nm,Anditisworthnotingthat(2.34±0.47nm)eventhrough1:1,whichrevealtheexcellentpingagent.

TheseresultsillustratethethroughreductionofCu2+whichenableextremelynumberofCu2+encapsulatedincreasingconcentrationofDA,CuNPs(whichwillbefurtherFig.3showsTEMimagesofconcentrationofcoppersalt(3:1)andcorrespondingTheparticlesbecomelargerasincreased.Atcoppersaltticlesizewas1.93±0.73nm(2.55±0.47nm(Fig.3c).Thismorenucleicouldbeformedsaltconcentrationandtheleadingtotheformationofpointingoutthatthesize(2.55±0.47nm)whenthehighas0.5M.Itdemonstratestivecappingagentevenat3.3.3.StabilityofCuNPsThestabilityofthedispersiontoresistin uentialfactorintheiragglomerationofaddedintoreactionsystem.reducingandcappingagentagent.Thewater-solublestability.Indeed,the8000rpmfor15minwassignsofsedimentationwerestorage,asprovedbythelongperiodofstorage(Fig.4theabsorbancespectrumchangesigni cantly,Moreover,thehighstabilityof rmedbythehighZetaobtainedis32mV,whichisstabilityforcolloidalDA-stabilizedCuNPsarepinganddispersioneffectofsystem.

3.4.Anti-oxidationstabilityofItisworthnotingthattheCuNPstendtobeeasilyoxidizedinairunderatmosphericconditionincomparisonwithnoblemetals

likegoldandsilver,whichwouldcontaintheirpotentialapplica-tionareas.Therefore,thesynthesisofCuNPswithanti-oxidation

44

J. Xiong et al./ Journal of Colloid and Interface Science 390 (2013) 41–46

Fig. 4. UV–Vis absorption spectra of CuNPs kept at ambient conditions over time. The inset shows the corresponding photo-graphs of samples.

(6 months), reveal clear lattice fringes with d-spacing of 2.1Å corresponding to the (1 1 1) lattice planes of metallic copper. The oxide-free and identical copper phase demonstrates that the DAstabilized CuNP

s dispersions could prevent the oxidation even after 6 months of storage. This anti-oxidation stability is likely attributed to the present of dopaminechrome capping layer at the surface of CuNPs. The steric effect arising from the ring structure of dopaminechrome on the surface of CuNPs may play an important role in prohibiting oxidation of CuNPs dispersions. 3.5. Fourier transform infrared (FT-IR) characterization FT-IR spectroscopy was used to investigate the interactions between different species and changes in chemical compositions of the mixtures. Fig. 6 shows the FT-IR spectrums for pure DA and the as-prepared CuNPs. The peak at 1290 cmÀ1 which assigned to C–O stretching vibration disappeared after the reaction and new peak was observed at 1630 cmÀ1. The peak attributed to the carbonyl groups of dopaminechrome (the oxidation product of DA), possibly because the transmission peaks toward higher energies result from the coupling of vibrations of the two-carbonyl and the conjugative effect. In addition, the peak at 3400 cmÀ1 observed for the as-prepared CuNPs assigned to N–H stretching vibration of dopaminechrome. These results evidenced the reduction process that DA converted into dopaminechrome. The presence of dopaminechrome on the surface of CuNPs provides excellent stability for colloidal dispersions (which will be discussed in detail in the mechanism section).

Fig. 3. TEM images of synthesized CuNPs with different concentrations of copper salt at molar ratio of DA to copper salt (3:1): (a) 0.1 M, d= 1.61± 0.44 nm; (b) 0.2 M, d= 1.93± 0.73 nm; (c) 0.3 M, d= 2.55± 0.47 nm. The insets show the representative HRTEM images and the size distribution of the CuNPs.

stability is an important issue that needs to be considered. The HRTEM images (Fig. 5), which took after a long period of storage

Fig. 5. HRTEM images of DA-stabilized CuNPs after 6 months storage.

3.6.ReductionandcappingmechanismofDA

Theaboveresultsshowthatwell-dispersedwater-solubleCuN-PscanbeobtainedthroughreductionofCu2+usingDAasbothreducingandcappingagent.Thehighlywater-solubleDA,asakind

ItisobservedthatDAservesasanelectrondonorininterac-tions,beingconvertedintodopaminequinoneandthendopamine-chrome.Inourpreviouswork[43],wehavesuccessfullysynthesizedCuNPsusingL-ascorbicacid,whoseredoxpotentialisoftensimilartothepotentialofdopamine[44,45].Therefore,dop-