碳量子点及其应用综述

Thisjournalis©TheRoyalSocietyofChemistry2014Chem.Soc.Rev.Citethis:DOI:10.1039/c4cs00269eCarbonquantumdotsandtheirapplicationsShiYingLim,WeiShenandZhiqiangGao*Fluorescentcarbonnanoparticlesorcarbonquantumdots(CQDs)areanewclassofcarbonnanomaterialsthathaveemergedrecentlyandhavegarneredmuchinterestaspotentialcompetitorstoconventionalsemiconductorquantumdots.Inadditiontotheircomparableopticalproperties,CQDshavethedesiredadvantagesoflowtoxicity,environmentalfriendlinesslowcostandsimplesyntheticroutes.Moreover,surfacepassivationandfunctionalizationofCQDsallowforthecontroloftheirphysicochemicalproperties.Sincetheirdiscovery,CQDshavefoundmanyapplicationsinthefieldsofchemicalsensing,biosensing,bioimaging,nanomedicine,photocatalysisandelectrocatalysis.ThisarticlereviewstheprogressintheresearchanddevelopmentofCQDswithanemphasisontheirsynthesis,functionalizationandtechnicalapplicationsalongwithsomediscussiononchallengesandperspectivesinthisexcitingandpromisingfield.1.IntroductionTheuniquepropertiesofcarbonicnanomaterialssuchasnano-diamonds,fullerenes,carbonnanotubes,graphenesheetsandfluorescentcarbonnanoparticlesorcarbonquantumdots(CQDs)haveinspiredextensivestudiesonthemduetotheirgreatpotentialforawidevarietyoftechnicalapplications.AmongtheelectronicandphysicochemicalcharacteristicsofCQDs,theiropticalpropertiesandtheirfluorescenceemissionsinparti-cularhaveattractedincreasinginterestinrecentyears.Formanyyears,semiconductorquantumdotshavebeenextensivelyinves-tigatedfortheirstrongandtunablefluorescenceemissionproperties,whichenabletheirapplicationsinbiosensingandbioimaging.However,semiconductorquantumdotspossesscertainlimitationssuchashightoxicityduetotheuseofheavymetalsintheirproduction.1–3Itisknownthatheavymetalsarehighlytoxicevenatrelativelylowlevels,whichmayproveprohibitivetoanyclinicalstudies.4,5ThispromptedthecreationofCQDstoreplacesemiconductorquantumdotsduetotheirlowtoxicity,biocompatibility,lowcostandchemicalinertnessinadditiontohavingsimilarfluorescenceproperties.TheaccidentaldiscoveryofCQDsduringtheseparationandpurificationofsingle-walledcarbonnanotubes(SWCNTs)byXuetal.in2004triggeredsubsequentstudiestoexploitthefluorescencepropertiesofCQDsandcreateanewclassofviablefluorescentnanomaterials.6Fluorescentcarbonnanoparticlesreceivedtheirname‘‘carbonquantumdots’’in2006fromSunetal.7whoproposedasyntheticroutetoproduceCQDswithmuchenhancedfluorescenceemissionsviasurfacepassivation.CQDsaresynthesisedbytworoutes,namelythetop-downroute7–9andthebottom-uproute.3,10–12CQDsaretypicallyquasi-sphericalDepartmentofChemistry,NationalUniversityofSingapore,Singapore117543.E-mail:[e-mail];Fax:[phone];Tel:[phone]ShiYingLimMsShiYingLimwasborninSingapore.ShereceivedherBScinChemistryfromtheNationalUniversityofSingaporein2014andiscurrentlyagraduatestudentintheDepartmentofChemistryatthesameinstitution.Herresearchfocusesoncamera-basedfluores-cencecorrelationspectroscopy.WeiShenMsWeiShenreceivedherBScinChemistryfromZhejiangUniver-sityin2011.SheiscurrentlyagraduatestudentintheDepart-mentofChemistryNationalUniversityofSingapore.Herresearchinterestsincludebio-sensorsandopticalassaysfornucleicacidsandproteins.Received4thAugust2014DOI:10.1039/c4cs00269e:12:54.ViewArticleOnlineViewJournalChem.Soc.Rev.Thisjournalis©TheRoyalSocietyofChemistry2014nanoparticlescomprisingamorphoustonanocrystallinecoreswithpredominantlygraphiticorturbostraticcarbon(sp2carbon)orgrapheneandgrapheneoxidesheetsfusedbydiamond-likesp3hybridisedcarboninsertions(Fig.1).13–16OxidisedCQDscontainconsiderableamountsofcarboxylmoietiesattheirsurface.Dependingonthesyntheticroute,theoxygencontentintheoxidisedCQDsrangesfrom5to50%(weight).14AsshowninFig.1,therearemanycarboxylmoietiesontheCQDsurface,whichimpartexcellentwatersolubilityandsuitablechemicallyreactivegroupsforfurtherfunctionalizationandsurfacepassiva-tionwithvariousorganic,polymeric,inorganicorbiologicalmaterialstoCQDs.Uponsurfacepassivation,thefluorescencepropertiesofCQDsareenhanced.Surfacefunctionalizationalsomodifiestheirphysicalproperties,liketheirsolubilityinaqueousandnon-aqueoussolvents.Asagroupofnewlyemergedfluorescentnanomaterials,CQDshaveshowntremendouspotentialasversatilenanomaterialsforawiderangeofapplications,includingchemicalsensing,biosensing,bioimaging,drugdelivery,photodynamictherapy,photocatalysisandelectrocatalysis.Comparedtoconventionalsemiconductorquantumdots,theuniqueattributesofCQDs,forexampletheirbenignchemicalcomposition,tunablefluores-cenceemissions,facilefunctionalizationandexcellentphysico-chemicalandphotochemicalstability(non-photobleachingornon-photoblinking),renderthemveryattractivefortechnicalapplications.Togetherwithotheradvantagessuchaslowcostandeaseofsynthesis,17CQDsareinafavourablepositionforachievingunprecedentedperformance.Ontheotherhand,complexproceduresfortheirseparation,purificationandfunctionalization,theirgenerallylowquantumyields,andambiguit