Luminol chemiluminescence induced by silver nanoparticles in(2)

186N.Lietal./JournalofPhotochemistryandPhotobiologyA:Chemistry215 (2010) 185–190

explored.ItisfoundthatAgNPsinthepresenceofNaBrandCu2+couldreactwithluminol,accompanyingbyaCLemission.TheCLmechanismwasalsostudied.2.Experimental

2.1.Chemicalsandsolutions

A1.0×10 2mol/Lstocksolutionofluminolwaspreparedbydissolvingluminol(Sigma,America)in0.10mol/Lsodiumhydrox-idesolution.Polyvinylpyrrolidone(PVP,Mw=36,000),superoxidedismutase(SOD),AgNO3,NaBr,NaI,NaCl,thiosulfate,CuSO4,andNaBH4wereobtainedfromShanghaiReagent(Shanghai,China).Allreagentswereofanalyticalgrade,andusedasreceived.Ultra-purewaterobtainedbyaDirect-Q3UVwaterpuri cationsystem(Millipore,USA)wasusedthroughout.2.2.PreparationofAgcolloid

AgColloidwassynthesizedbychemicalreductionmethodinasolution.Inbrief,0.50gPVPwasdissolvedin20.0mLwater.Subsequently,25mLNaBH4(5.0×10 3mol/L)wasmixedwiththePVPaqueoussolution.Then,5.0mLAgNO3(5.0×10 3mol/L)wereaddeddropwisetothemixturewithvigorousstirringsimultane-ously.Thecolorofthemixturevisiblychangedtoyellowgradually.Thereactionwasconductedatroomtemperaturefor30minandagedfor2daysat4 Cbeforeuse.Therawcolloidwascentrifugedat12,500rpmfor30min(Universal320,Hettich,Germany).Agcolloidwasobtainedafterthesedimentwasredissolvedin1%PVPaqueoussolution.Theresultingyellowsilvercolloidswerecharacterizedbyhighresolutiontransmissionelectronmicroscope(HRTEM,JEM-2010,Hitachi,Japan).ThediametersandsizedistributionofAgNPswereobtainedbasedonthestatisticalanalysisofHRTEMdataasshowninFig.1.TheimageofFig.1showedtheAgNPswerewelldistributed.StatisticalanalysisofHRTEMdatarevealedthattheaveragediameteroftheNPswas8.0±4.0nm.2.3.CLmeasurements

TheCLwasdetectedbyamicroplateluminometer(CentroLB960,Berthold,Germany).Inatypicalexperiment,themixedsolu-tionof50 LofAgcolloidwith50 LofNaBrwaspipetted

into

Fig.1.HRTEMimagesofAgNPs.TheinsetisthecorrespondingsizedistributionsofAgNPs.Calculateddiameteris8.0±4.0nmbyaccountingabout100units.

eachwellofmicrotiterplate,andthen50 LofCuSO4and50 Lofluminolwereinjectedintothemixtureinthewellsuccessively.Thelightemissionwasmeasuredbythemicroplateluminometerimmediately.

2.4.Opticalmeasurements

TheCLspectraweremeasuredonamodelFL5401spectro u-orometer(Shimadzu,Japan).UV–visspectraweremeasuredonamodelUV-2401PCspectrophotometer(Shimadzu,Japan).ThereactionproductoftheAgcolloid–NaBr–CuSO4systemwascharac-terizedbyX-raypowderdiffraction(XRD)andX-rayphotoelectronspectrum(XPS).XRDpatternwasobtainedwithamodelD/max-rAdiffractometer(Rigaku,Japan)andXPSwasobtainedwithamodelESCALABMKIIelectronspectrograph(VG,England).Thesamplewaspreparedasfollows:4mLCuSO4(0.1mol/L)wasaddedinto400mLAgcolloidcontaining1.0×10 2mol/LNaBr.Thesolutionwascontinuouslystirredfor60min.Afterthereaction nishedcompletely,thereactedsystemwasevaporatedandprecipitatesoccurredinthereactedmixturegradually.Then,theobtainedpre-cipitateswere ltratedbyamixedcellulosemembranewithporesizeof0.45 m(XingYa,Shanghai).Subsequently,theprecipitateswerethoroughlywashedbywaterandethanolandthendriedatroomtemperatureforanight,whichwasusedforthefurtherexper-iments.

3.Resultsanddiscussion

3.1.CLaccompaniedbyreactionofluminol–CuSO4–AgNPsinthepresenceofNaBr

TheCLresponseofAgNPsinthepresenceofNaBrandCuSO4toalkalineluminolsolutionwasstudiedbystaticinjection.AsshowinFig.2, rst,whenAgcolloidwasmixedwithNaBr,noCLemis-sionappeared(thelinesbeforeinjection).Subsequently,CuSO4andluminolwereinjectedtothemixturesuccessively,arepro-ducibleCLwasobserved(curvea).ThemaximumCLintensityoftheCLsystemwasaboutoneorderofmagnitudehigherthanthatofaconventionalluminol–H2O2CLsystem(0.001mol/LH2O2)withthesamepHvalueoftheCLreactionandthesameconcentrationofluminol.ThesupernatantoftheAgcolloidaftercentrifugationwasusedasacontrolsolutionfortheCLexperimentsinsteadofAgcolloidandnoconsiderableCLemissionwasobserved

(curve

Fig.2.ChemiluminescencekineticcurveswheninjectingCuSO4andluminolintoAgcolloidinthepresenceofNaBr(a).Thesupernatantsolutionaftercentrifuga-tionofAgcolloidwasusedasacontrolsolution(b).Reactionconditions:CuSO4,1×10 3mol/L;luminol,1×10 4mol/Lin0.1mol/Lcarbonatebuffer(pH10.0);Ag,3×10 4mol/L;NaBr,1×10 2mol/L.Theinsetisthechemiluminescencespectra.