介孔氧化硅药物控制释放,pH荧光检测,聚合物交联

FluorescentpH-SensingOrganic/InorganicHybridMesoporousSilicaNanoparticleswithTunableRedox-ResponsiveReleaseCapability

XuejuanWan,DiWang,andShiyongLiu*CASKeyLaboratoryofSoftMatterChemistry,DepartmentofPolymerScienceandEngineering,HefeiNationalLaboratoryforPhysicalSciencesattheMicroscale,UniversityofScienceandTechnologyofChina,Hefei,Anhui230026,ChinaReceivedMay26,2010.RevisedManuscriptReceivedAugust4,2010WereportonthefabricationoffluorescentpH-sensingorganic/inorganichybridmesoporoussilicananoparticles(MSN)capableoftunableredox-responsivereleaseofembeddedguestmolecules.Thereversibleaddition-fragmenta-tionchaintransfer(RAFT)copolymerizationofN-(acryloxy)succinimide(NAS),oligo(ethyleneglycol)monomethylethermethacrylate(OEGMA),and1,8-naphthalimide-basedpH-sensingmonomer(NaphMA)atthesurfaceofMSNledtofluorescentorganic/inorganichybridMSN.TheobtainedhybridMSNexhibitsexcellentwaterdispersibilityandactsassensitivefluorescentpHprobesintherangepH4-8duetothepresenceofNaphMAmoieties.AfterloadingwithrhodamineB(RhB)asamodeldrugmolecule,P(NAS-co-OEGMA-co-NaphMA)brushesatthesurfaceofhybridMSNwerecross-linkedwithcystaminetoblocknanoporeentrancesfortheeffectiveretentionofguestmolecules.Takingadvantageofdisulfide-containingcross-linkers,thereleaserateofRhBcanbeeasilyadjustedbyaddingvaryingconcentrationsofdithiothreitol(DTT),whichcancleavethedisulfidelinkagetoopenblockednanopores.TheincreaseofDTTconcentrationfrom0to20mMledto20-30timesenhancementofRhBreleaserate.ThereportedmultifunctionalhybridMSNaugurswellforapplicationsincontrolled-releasenanocarriers,cellandtissueimaging,andclinicaldiagnosis.IntroductionSelf-assembledsmartdrugnanocarrierssuchasliposomes,blockcopolymermicelles,vesicles,andcapsulesthatcantrapguestmoleculesandreleasethemunderaspecificexternalstimulus(e.g.,pH,temperature,light,andbioactivemolecules)oracombinationofthemhavebeenextensivelyexploredinthepastdecades.1-4Generally,thesesupramolecularassembliespossessinherentlim-itationssuchasinsufficientstructuralstabilityandlowdrugloadingefficiency.Afterintravenousadministration,thehighdilutionandlargeshearforcesduringbloodcirculationcanleadtostructuraldisintegrationofdrugnanocarriers.Forblockcopo-lymermicellesandvesicles,coreorshellcross-linkingapproacheshavebeenutilizedtopartiallysolvethestructuralstabilityproblem.5However,theiruseascontrolleddeliveryvehiclesforhydrophilicdrugsstillposesaconsiderablechallenge.Asanalternativetodrugnanocarriersconstructedfrompolymericmaterials,inorganicmaterialssuchasmesoporoussilicananoparticles(MSN)holdgreatpromiseasnew-generationsmartdrugnanocontainersduetotheirhighstability,largesurfaceareas,tunableporesizes,andabundantsurfacefunctionalization*Towhomcorrespondenceshouldbeaddressed.E-mail:sliu@ustc.edu.cn.sites.6-10OneofthekeyissuesindesigningMSN-baseddrugdeliveryvehiclesistodevelopnovelstrategiesfortheon/offswitchingofnanopores,i.e.,blockingthenanoporeentrancesafterencapsulatingdrugmoleculesanduncappingthemfortriggeredreleaseunderspecificexternalstimuli.Previously,var-ioustypesofnanoparticles,11-16organicmolecules,17-26andpolymerchainsorbrushes27-30withhydrodynamicsizescompar-abletoorlargerthanthenanoporeentrancesofMSNwere(11)Giri,S.;Trewyn,B.G.;Stellmaker,M.P.;Lin,V.S.Y.Angew.Chem.,Int.Ed.2005,44,5038–5044.(12)Vivero-Escoto,J.L.;Slowing,I.I.;Wu,C.W.;Lin,V.S.Y.J.Am.Chem.Soc.2009,131,3462–3463.(13)Torney,F.;Trewyn,B.G.;Lin,V.S.Y.;Wang,K.Nat.Nanotechnol.2007,2,295–300.(14)Lee,J.E.;Lee,N.;Kim,H.;Kim,J.;Choi,S.H.;Kim,J.H.;Kim,T.;Song,I.C.;Park,S.P.;Moon,K.M.;Hyeon,T.J.Am.Chem.Soc.2010,132,552–557.(15)Liu,R.;Zhang,Y.;Zhao,X.;Agarwal,A.;Muller,L.J.;Feng,P.Y.J.Am.Chem.Soc.2010,132,1500–1501.(16)Aznar,E.;Marcos,M.D.;Martinez-Manez,R.;Sancenon,F.;Soto,J.;Amoros,P.;Guillem,C.J.Am.Chem.Soc.2009,131,6833–6843.(17)Nguyen,T.D.;Leung,K.C.F.;Liong,M.;Liu,Y.;Stoddart,J.F.;Zink,J.I.Adv.Funct.Mater.2007,17,2101–2110.(18)Schlossbauer,A.;Kecht,J.;Bein,T.Angew.Chem.,Int.Ed.2009,48,3092–3095.(19)Patel,K.;Angelos,S.;Dichtel,W.R.;Coskun,A.;Yang,Y.W.;Zink,J.I.;Stoddart,J.F.J.Am.Chem.Soc.2008,130,2382–2383.(20)Mal,N.K.;Fujiwara,M.;Tanaka,Y.Nature2003,421,350–353.(21)Lu,J.;Choi,E.;Tamanoi,F.;Zink,J.I.Small2008,4,421–426.(22)Angelos,S.;Yang,Y.W.;Patel,K.;Stoddart,J.F.;Zink,J.I.Angew.Chem.,Int.Ed.2008,47,2222–2226.(23)Climent,E.;Bernardos,A.;Martinez-Manez,R.;Maquieira,A.;Marcos,M.D.;Pastor-Navarro,N.;Puchades,R.;Sancenon,F.;Soto,J.;Amoros,P.J.Am.Chem.Soc.2009,131,14075–14080.(24)Park,C.;Kim,H.;Kim,S.;Kim,C.J.Am.Chem.Soc.2009,131,16614–16615.(25)Ferris,D.P.;Zhao,Y.L.;Khashab,N.M.;Khatib,H.A.;Stoddart,J.F.;Zink,J.I.J.Am.Chem.Soc.2009,131,1686–1687.(26)Bernardos,A.;Aznar,E.;Marcos,M.D.;Martinez-Manez,R.;Sancenon,F.;Soto,J.;Barat,J.M.;Amoros,P.Angew.Chem.,Int.Ed.2009,48,5884–5887.(27)Liu,R.;Zhao,X.;Wu,T.;Feng,P.Y.J.Am.Chem.Soc.2008,130,14418–14419.(28)Liu,R.;Zhang,Y.;Feng,P.Y.J.Am.Chem.Soc.2009,131,15128–15129.(1)Peer,D.;Karp,J.M.;Hong,S.;FarokHzad,O.C.;Margalit,R.;Langer,R.Nat.Nanotechnol.2007,2,751–760.(2)Torchilin,V.P.Adv.DrugDeliveryRev.2006,58,1532–1555.(3)Discher,D.E.;Ortiz,V.;Srinivas,G.;Klein,M.L.;Kim,Y.;David,C.A.;Cai,S.S.;Photos,P.;Ahmed,F.Prog.Polym.Sci.2007,32,838–857.(4)Rapoport,N.Prog.Polym.Sci.2007,32,962–990.(5)Thurmond,K.B.;Kowalewski,T.;Wooley,K.L.J.Am.Chem.Soc.1996,118,7239–7240.(6)Stein,A.;Melde,B.J.;Schroden,R.C.Adv.Mater.2000,12,1403–1419.(7)Saha,S.;Leung,K.C.F.;Nguyen,T.D.;Stoddart,J.F.;Zink,J.I.Adv.Funct.Mater.2007,17,685–693.(8)Vallet-Regi,M.;Balas,F.;Arcos,D.Angew.Chem.,Int.Ed.2007,46,7548–7558.(9)Manzano,M.;Vallet-Regı,M.J.Mater.Chem.,DOI:10.1039/b922651f.(10)Wang,Y.J.;Caruso,F.Chem.Mater.2005,17,953–961.15574DOI:10.1021/la102148xPublishedonWeb09/14/2010Langmuir2010,26(19),15574–15579

Wanetal.Article

Scheme1.SchematicIllustrationfortheSynthesisofpH-SensingOrganic/InorganicHybridMesoporousSilicaNanoparticles(MSN)CoatedwithP(NAS-co-OEGMA-co-NaphMA)Brushes,TheirCross-LinkingwithCystamine,andRedox-ResponsiveReleaseof

EmbeddedRhodamineB(RhB)Dyes

employedtoeffectivelypreventthereleaseofencapsulatedguestmolecules.Asforthetriggeredreleasemechanisms,photoswitchablecis-transisomerization,21,25photolabile12,16,17,24orpH-labile15,16covalentlinkages,enzyme-catalyzeddegradation,19,24andreversiblenoncovalentinteractions(electrostaticinteraction,12supramolecu-larrecognition16,22,23,25)havebeentypicallyemployed.Recently,Linetal.12utilizedpositivelychargedgoldnanopar-ticlestoblockthenanoporesofMSNviaelectrostaticinteraction.UponUVirradiation,goldnanoparticlesexhibitsurfacechargereversalbehaviorduetothepresenceofphotolabileo-nitrobenzylestermoiety,leadingtotheuncappingofMSNnanopores.ZinkandStoddartetal.25functionalizedtheMSNsurfacewithazobenzenederivatives,andtheirsupramolecularrecognitionwithβ-cyclodextrin(β-CD)caneffectivelyblocktheMSNnanopores.Toavoidtheuncontrolledreleaseofguestmoleculesfrompolymerbrush-coatedMSN,Fengetal.27synthesizedpoly(N-(acryloxy)succinimide)(PNAS)-coatedMSNviasur-face-initiatedreversibleaddition-fragmentationchaintransfer(RAFT)polymerizationandcross-linkedthepolymerbrusheswithcystaminetocaptheMSNnanoporeentrances.Theuncap-pingcanbeeasilyachievedviatheadditionofdithiothreitol(DTT)toinducecleavageofdisulfidebonds.Mostrecently,theyfurthermodifiedPNAS-coatedMSNwithβ-CDthroughadisulfidelinkage,theadditionofdiazolinkercanalsocross-linkthepolymerbrushes;mostimportantly,theuncappingcanbeinducedbymultiplestimuli,suchasphotoirradiation,theadditionofDTT,orexcessβ-CD.28ItshouldbenotedthatalltheaboveexamplesofMSN-baseddrugnanocarriershavefocusedondevelopingnewtriggered-releasestrategies.Undercertaincircumstances,itishighlydesirabletoendowMSN-basednanocarrierswithmulti-functionssuchasdetectionandtargeteddelivery.Forexample,inlivingorganisms,intracellularpHplayskeyrolesinenzyme,cell,andtissueactivities,andmicroenvironments(29)Hong,C.Y.;Li,X.;Pan,C.Y.J.Phys.Chem.C2008,112,15320–15324.(30)Pollak,A.;Blumenfeld,H.;Wax,M.;Baughn,R.L.;Whitesides,G.M.J.Am.Chem.Soc.1980,102,6324–6336.inendosomes(pH5.5-6)andlysosomes(pH4.5-5)aremildlyacidic.Besides,sometumorcellspossesslowerextracellularpH(pH6.4-6.9)comparedtonormaltissues(pH7.2-7.4).Thus,monitoringpHchangesandgradientsarequiteimportanttodeterminetheefficiencyofpharmaceuticaltherapy,diagnosecertaincancerdiseases,andinvestigatecellularinternalizationpathways.IfMSN-baseddrugnanocarriersareendowedwithpH-sensingability,theymightbequiteusefulinpracticalapplica-tionsforsimultaneouschemotherapyandthemonitoringoftherapeuticefficiency;moreover,thisnoveltypeofmultifunc-tionalMSN-basednanocarrierscanbequiteadvantageoustoinvestigatethedrugnanocarriers-cellinteractionsandunder-standtheunderlyingmechanism.Herein,wereportonthefabricationofmultifunctionalfluor-escentorganic/inorganichybridMSNpossessingpH-probingandtunableredox-responsivereleaseproperties.RandomcopolymerscomposedofN-(acryloxy)succinimide(NAS),oligo-(ethyleneglycol)monomethylethermethacrylate(OEGMA),and1,8-naphthalimide-basedfluorescentpH-sensingmonomer(NaphMA)wereanchoredatthesurfaceofMSNviasurface-initiatedRAFTpolymerization(Scheme1).TheobtainedhybridMSNexhibitsexcellentwaterdispersibilityandcanactassensitivefluorescentpHprobeintherangeofpH4-8duetothepresenceofNaphMAmoieties.Moreover,afterloadingwithmodeldrugmolecules,rhodamineB(RhB),andcross-linkingthepolymerbrusheswithcystamine,theredox-responsivereleaseofencapsulatedguestmoleculesfromorganic/inorganicMSNcanbefacilelytunedbyvaryingtheconcentrationsofexternallyaddedDTT.Asfarasweknow,thisrepresentsthefirstreportofendowingMSN-basedtriggered-releasenanocarrierswithpHsensingfunctions.ResultsandDiscussionSyntheticschemesemployedforthepreparationofmultifunc-tionalfluorescentorganic/inorganichybridMSNpossessingpH-probingabilityandtunableredox-responsivereleasepropertiesDOI:10.1021/la102148x

Langmuir2010,26(19),15574–1557915575

Article

Scheme2.SyntheticSchemesEmployedforthePreparationof1,8-Naphthalimide-BasedpH-SensingFluorescentMonomer(NaphMA,4)

areshowninScheme1.Surface-initiatedRAFTcopolymerizationofNAS,OEGMA,and1,8-naphthalimide-basedfluorescentpH-sensingmonomer(NaphMA)fromMSNledtoorganic/inorganichybridMSNcoatedwithP(NAS-co-OEGMA-co-NaphMA)randomcopolymerbrushes.Theyweresubjecttotheloadingofmodeldrugmolecules,RhB,andsubsequentcross-linkingwithcystamine.Synthesisof1,8-Naphthalimide-BasedpH-SensingMonomer(NaphMA,4).pH-sensingfluorescentmonomer,NaphMA(4),wassynthesizedviafoursteps,startingfrom4-bromo-1,8-naphtha-licanhydride(Scheme2).Thereactionbetween4-bromo-1,8-naphthalicanhydrideand4-(2-aminoethyl)morpholinewasper-formedin1,4-dioxideunderreflux.The1HNMRspectrumofcompound1isshowninFigureS1(SupportingInformation).Resonancesignalsat3.49ppm(peaka)and2.42ppm(peakb)areassignedtomethyleneprotonsinthemorpholinemoiety.Allotherresonancesignalscanbewellassigned,indicatingthesuccessfulpreparationofcompound1.Compound2wassynthesizedbythesubstitutionreactionofcompound1inthepresenceofsodiumazide.Its1HNMRspectrumisshowninFigureS1(SupportingInformation),togetherwiththepeakassignments.Theresonancesignalascribedtothenaphthalimideprotonneighboringthebrominesubstituent(peakf)shiftsfrom7.9to7.4ppmafterazidation,accompaniedbyaconsiderableshiftofotherresonancesignalsofnaphthalimideprotonsintheNMRspectrumof2,ascomparedtothoseof1.Theazidemoietyin2wasconvertedtoamineinthepresenceofzincpowderandammoniumchloride,andtheobtained3wasfurtherreactedwithmethacrylicanhydridetogivethetargetcompound(4).1HNMRspectraof3and4areshowninFigureS2(SupportingInformation),togetherwiththepeakassignments.Comparedtothosein2,resonancesignalscharacteristicofnaphthalimideproton(peakf)intheNMRspectrumof3exhibitconsiderableshiftfrom7.4ppmto6.8ppm,indicatingthatazidomoietieswerecompletelyconvertedtoaminefunctionality.Aftertheamidationreaction,wecanclearlyobservetheappearanceofmethacrylamide1doublebondatδ=5.7and6.0ppm.ForalltheHNMRspectraofcompounds1-4,bothpeakassignmentsandpeakintegralratiosconfirmthesuccessfulpreparationofthem.PreparationofHybridMSNCoatedwithP(NAS-co-OEGMA-co-NaphMA)Brushes.First,MCM-41wasprepared(31)Mitsukami,Y.;Donovan,M.S.;Lowe,A.B.;McCormick,C.L.Macro-molecules2001,34,2248–2256.(32)Radu,D.R.;Lai,C.Y.;Wiench,J.W.;Pruski,M.;Lin,V.S.Y.J.Am.Chem.Soc.2004,126,1640–1641.15576DOI:10.1021/la102148xWanetal.

Figure1.TEMimagesof(a)and(b)mesoporoussilicaMCM-41,(c)organic/inorganichybridMSNcoatedwithP(NAS-co-OEG-MA-co-NaphMA)brushes,and(d)organic/inorganichybridMSNcoatedwithcross-linkedpolymerbrushessubjectedtoHFtreatmentfor15min.accordingtoliteratureprocess,32.33whichhasbeenwell-knowntoproducesphericalmesoporoussilicananoparticleswithrelativelynarrowsizeandhomogeneousporedistribution.TheobtainedMCM-41wastreatedwithEHTEStointroduceepoxyfunctional-ities,followedbyremovingCTABtemplatesbyrefluxingovernightinamethanolicsolutionofHCl(1.5M).Duringthesameprocess,epoxymoietiesatthesurfaceofMSNwerealsoconvertedto5,6-dihydroxyhexylfunctionalities.TheorderedmesoporousstructureandtheparticlemorphologyareconfirmedbyX-raydiffraction(XRD,FigureS3,SupportingInformation),HRTEM(Figure1),andN2adsorptionmeasurements(FigureS4,SupportingIn-formation).TheobtainedMSNpossessesanaveragediameterof150(15nm(Figure1a,b)withBETsurfacesofapproximately1024m2/gandanaverageporesizeof∼2.6nm(FigureS4,SupportingInformation).FurtherfunctionalizationofMSNwithRAFTagentswasachievedviaDCC-mediatedesterificationinthepresenceofaRAFTagent,CPAD.Decreasingweightretentionsfrom96.7%fornakedMSN,95.4%forepoxy-functionalizedMSN,and93.3%forCPAD-functionalizedMSNareobserved1intheTGAcurves(Figure2).Besides,anewbandat1730cm-characteristicoftheestercarbonylgroupappearsforCPAD-functionalizedMSNintheFT-IRspectrum(FigureS5,SupportingInformation),clearlyindicatingthecovalentattachmentofCPADagentontoMSN.However,itisquitedifficulttocalculatethedensityoffunctiona-lizationsitesatthesurfaceofMSNbecausethevolumetricmassdensityofMSNcannotbeaccuratelydetermined.Threecomonomerswerechosenforthesurface-initiatedRAFTcopolymerizationfromMSN.HydrophilicOEGMAwasincorporatedintograftedpolymerbrushestoenhancethewaterdispersibilityofhybridMSNwithimprovedbiocompat-ibility,whereastheincorporationofNaphMAresiduescanendoworganic/inorganichybridMSNwithpH-sensingability.NASresiduesarewell-knownfortheirremarkablereactivityforprimaryamines.Thus,theincorporationofNASintopoly-merbrushescanallowforthefacilecross-linkingwithcystamine.Previously,McCormicketal.31,34reportedthesynthesisof(33)vonWerne,T.;Patten,T.E.J.Am.Chem.Soc.2001,123,7497–7505.(34)Li,Y.T.;Lokitz,B.S.;McCormick,C.L.Macromolecules2006,39,81–89.Langmuir2010,26(19),15574–15579

Wanetal.Figure2.TGAcurvesof(a)puremesoporoussilicaMCM-41,(b)epoxy-functionalizedMSN,(c)mesoporoussilicasurfacefunctionalizedwithRAFTmediatingagent,andorganic/inorganichybridMSNcoatedwithP(NAS-co-OEGMA-co-NaphMA)brushes(d)beforeand(e)aftercross-linkingwithcystamine.PEO-P(DMA-co-NAS)-PNIPAMtriblockcopolymerinwhichPEO,DMA,andNIPAMarepoly(ethyleneoxide),N,N-dimethy-lacrylamide,andN-isopropylacrylamide,respectively.Takingad-vantageoftheNASresidues,self-assembledmicellesatelevatedtemperaturescanbecross-linkedwithcystamine.Moreover,thecross-linkingisreversibleduetothepresenceofredox-reactivedisulfidebonds.Thesurface-initiatedRAFTpolymerizationofNAS,OEGMA,andpH-sensingmonomerNaphMAatthesurfaceofMSNwasconductedin1,4-dioxaneat70°Cwithafeedratioof6:4:0.08.TheobtainedhybridMSNexhibitsmuchbetteraqueousdispersibilitycomparedtotheas-preparedMSN.Theaqueousdispersion(0.1g/L)ofhybridMSNshowsnomacroscopicphaseseparationuponstandingatroomtemperatureformorethan1week.HRTEMwasemployedtocharacterizethecore-shellnanostruc-turesoforganic/inorganichybridMSN,andtheresultsareshowninFigure1.TheporechannelsoftheaspreparedMSNarehomogeneouslyarranged,endowingadequatespacefortrappingguestmolecules.AsforhybridMSNcoatedwithP(NAS-co-OEGMA-co-NaphMA)brushes,apolymericnanoshellcanbeclearlydiscernedattheexteriorsurfaceofMSN.Thethicknessofthepolymerbrushesisapproximately20nm.AfterRAFTpolym-erization,theweightretentionoforganic/inorganichybridMSNfurtherdecreasesto49.8%,asevidencedfromTGAanalysisresults(Figure2).UsingCPAD-functionalizedMSNasareference,theweightfractionofP(NAS-co-OEGMA-co-NaphMA)brushlayersinorganic/inorganichybridMSNis∼46.6%.FT-IRspectraofpuremesoporoussilicaMCM-41andhybridMSNcoatedwithP(NAS-co-OEGMA-co-NaphMA)brushesareshowninFigureS5(SupportingInformation).AscomparedtothecaseofpureMSN,newbandsat1809,1780,and1740cm-1appearedinhybridMSNbeforecross-linking.TheformertwobandsarecharacteristicofcycliccarbonylinNASmoieties,whereasabsorbancepeaksat∼1740cm-1arecharacteristicoftheestercarbonylofbothOEGMAandNASresidues.Thus,FT-IRanalysisresultsindicatethesuccessfulsurfacegrafting.Forthecharacterizationofmolecularweightandmolecularweightdistributionofgraftedpolymerchains,hybridMSNcoatedwithP(NAS-co-OEGMA-co-NaphMA)brusheswerereactedwithn-butylaminetofullyconvertreactiveNASmoietiestoN-n-butylacrylamide(nBAM)residues,graftedpolymerchainswerethencleavedfromthesurfaceofMSNbytreatingwithhydrofluoricacid.TheGPCtraceofcleavedP(nBAM-co-OEGMA-co-NaphMA)chainsisshowninFigureS6(SupportingInformation),revealinganMnof37300andanMw/Mnof1.23.TherelativelynarrowpolydispersityindexandsymmetricGPCelutionpeakimpliesthatLangmuir2010,26(19),15574–15579

Article

thesurface-initiatedRAFTpolymerizationisconductedinacontrolledmanner.The1HNMRspectrumofcleavedpolymerchainsisalsoshowninFigureS6(SupportingInformation).ThenBAM/OEGMAmolarratioiscalculatedtobe5.8:4.2onthebasisoftheintegralratioofpeaksatof.AstheNaphMAfeedratioisquitelow(∼0.8mol%),itsmolarcontent(∼0.7mol%)wasdeterminedbyfluorescencemeasurementsinmethanol.DTT-RegulatedReleaseofGuestMoleculesfromHybridMSNCoatedwithCross-linkedPolymerBrushes.Pre-viously,Hongetal.29,35synthesizedhybridMSNcoatedwithpH-responsivepoly(acrylicacid)(PAA)orthermoresponsivepoly(N-isopropylacrylamide)(PNIPAM)brushes.AlthoughthereleaseprofileofencapsulateddrugscanbeadjustedviaexternalpHortemperaturechanges,covalentlygraftedpolymerbrushescannotcompletelyblocknanoporeentrancesanddrugleakagefromMSN-basednanocarriersbeforearrivingatthetargetsitemightoccur.InrecentworksbyFengetal.27concern-inghybridMSN-basednanocarriers,polymerbrushescross-linkedbydisulfide-containingdifunctionalspecies,orsupramo-lecularrecognitionbetweenβ-CDandazobenzenemoieties28wereemployedtoeffectivelyblocknanoporeentrances.Mostimportantly,triggeredreleaseofguestmoleculescanbeachieved.Inthecurrentwork,wecopolymerizedwater-solublemonomer(OEGMA)andpH-sensingmonomer(NaphMA)intoPNASbrushesgraftedatthesurfaceofhybridMSNtoenhanceitswater-dispersibilityandendownanocarrierswithsensingfunctions.P(NAS-co-OEGMA-co-NaphMA)brushesanchoredatthesurfaceofMSNwerecross-linkedwithcystamine.AcomparisonofTGAanalysisresults(Figure2)ofhybridMSNcoatedwithpolymerbrushesbeforeandaftercross-linking,49.8%and51.4%weightretention,respectively,revealsthat∼90%ofNASresidueshavereactedwithcystamine.ConsideringthattheamidationreactionofNASwithcystaminemightalsooccurinanintrachainmanner,whichdoesnotcontributetoeffectivecross-linking,theactualdegreeofcross-linkingshouldbelessthan90%.TheFT-IRspectrumoforganic/inorganichybridMSNcoatedwithcross-linkedbrushesisalsoshowninFigureS5(SupportingIn-formation).Aftercross-linking,absorptionbandsataround1780-1810cm-1characteristicofthecycliccarbonylgroupinNAScompletelydisappear,accompaniedby-the1appearanceofabsorptionpeaksataround1558-1643cm,whicharechar-acteristicofamidefunctionalities.Thus,bothTGAandFT-IRresultsconfirmsuccessfulcross-linkingofP(NAS-co-OEGMA-co-NaphMA)brushes.XRDresults(FigureS3,SupportingInformation)indicatethataftercross-linking,peakintensitiesat110,200,and210considerablydecrease,whichshouldbeascribedtothepore-fillingeffectinducedbycross-linking.Nitrogenadsorption-desorptionexperimentsareshowninFigureS4(SupportingInformation).AtypicaltypeIVisothermofmeso-porousmaterialswasobservedfortheaspreparedMSN,whereasorganic/inorganichybridMSNcoatedwithcross-linkedpolymerbrushesapparentlyexhibitsisothermcharacteristicofnonporousmaterials.Moreover,BETsurfaceareassharplydecreasedto86.7m2/gforhybridMSNcoatedwithcross-linkedbrushes.ThisindicatesthattheentrancesofMSNnanoporeshavebeeneffectivelycapped.Toverifythesuccessfulcross-linkingofP-(NAS-co-OEGMA-co-NaphMA)brushes,thehybridMSNwasfurthertreatedwithHFfor15min,andtheactualmorphologywasexaminedbyTEM(Figure1d).Wecanclearlyobservethepresenceofnanocapsules(Figure1d,diffusecoronasaroundspotswithhighercontrast).Thissuggeststhatthegraftedpolymerbrushesweresuccessfullycross-linked.(35)Hong,C.Y.;Li,X.;Pan,C.Y.J.Mater.Chem.2009,19,5155–5160.DOI:10.1021/la102148x15577

ArticleFigure3.TimeevolutionofdyereleaseinthepresenceofvaryingconcentrationsofDTT(0-20mM)fororganic/inorganichybridMSNcoatedwithcross-linkedpolymerbrushesandencapsulatedwithRhB.RhBwasthenutilizedasamodeldrugtoevaluatethecontrolledreleasecapabilityofhybridMSNcoatedwithcross-linkedpolymerbrushes.ReleaseprofilesofRhBfromhybridMSNcoatedwithcross-linkedpolymerbrusheswerethendeter-mined,andtheresultsareshowninFigure3.IntheabsenceofDTT,thereleaseofRhBisveryslow,indicatingthatthecross-linkingreactioncaneffectivelyblocknanoporeoutlets.Ontheotherhand,whenDTTconcentrationvariesintherange0-20mM,wecanapparentlyobservethedramaticenhancementofRhBreleaserate,whichincreaseswithincreasingDTTconcentrations.DTTcaninducethecleavageofdisulfidecross-linker,leadingtotheopeningofblockednanoporeentrances.Acomparisonofreleaseprofilesobtainedinthepresenceof0.02and20mMDTTrevealedthatlowconcentrationsofDTTareadvantageousforsteadyandcontrolledRhBrelease.BychangingtheDTTcon-centrationintherangeof0-20mM,wecanfinelyadjusttheRhBreleaseprofiles.Additionally,thecopolymerizationofOEGMAresiduesintopolymerbrushescanconsiderablyimprovethewaterdispersibilityofhybridMSN.Organic/InorganicHybridMSNforFluorescentpHSensing.TheprobingofpHgradientsandchangesarequitecrucialtodeterminetheefficiencyofpharmaceuticaltherapy,diagnosecertaincancerdiseases,andinvestigatecellularinter-nalizationpathways.Thechoiceofsuitablefluorescentdyes,oracombinationofthem,isquitecriticalfortheconstructionofsuitablepHprobes.Amongthem,smallmoleculenaphthalimidederivativescontainingarenedicarboximidefluorophoresandamineacceptorsforprotonsarequiteintriguing.36,37Thepro-tonationordeprotonationofaminemoietiescaninducethefluorescenceon-offswitchingofnaphthalimidereportersviathephotoinducedelectrontransfer(PET)mechanism,leadingtothesensitiveprobingofpHchanges.Naphthalimide-basedpH-detectingmotifscanevenbephysicallyembeddedintopolymerfilmstoconstructoptodemacrodevices,whichcanbeappliedinpracticalcircumstances.However,smallmoleculefluorescentpHprobesphysicallyembeddedinapolymermatrixhaveinherentlimitationssuchasleachingandpoorwatersolubility.Inthecurrentcase,wechoosetocovalentlyattachthenaphthalimide-basedpH-detectingmotiftohydrophilicpolymerbrushesanchoredonwater-dispersiblehybridMSNviatheRAFTcopolymerizationapproach.1,8-Naphthalimide-basedfluorescentpH-sensingmonomer(NaphMA,4)containsamorpholineacceptorforprotons,anarenedicarboximidefluorescencereporter,andaC2spacer.Inagreementwiththespectrofluorometricpropertiesofother(36)Daffy,L.M.;deSilva,A.P.;Gunaratne,H.Q.N.;Huber,C.;Lynch,P.L.M.;Werner,T.;Wolfbeis,O.S.Chem.;Eur.J.1998,4,1810–1815.(37)deSilva,A.P.;Rice,T.E.Chem.Commun.1999,163–164.15578DOI:10.1021/la102148x

Wanetal.

Figure4.(a)Fluorescencespectraand(b)fluorescenceintensitychanges(λwidths,em=478nm)recordedinthepHrange3-10(λex5nmandem5nm;25°C)fororganic/inorganicex=350nm;slithybridMSNcoatedwithcross-linkedpolymerbrusheswithoutloadingofguestmolecules.Figure5.Fluorescenceintensitychangesrecordedfortheaqueousdispersionoforganic/inorganichybridMSNcoatedwithcross-linkedpolymerbrushesunderpHcyclingof4-7uponalternateadditionofacidandbase.naphthalimide-basedderivativesasreportedbyWolfbeis’re-searchgroup,36theabsorbancespectraof4exhibitnearlynochangesoverthepHrange3-10(FigureS7,SupportingIn-formation).Thisadvantageisquiteimportantfortheconstruc-tionofpHprobeswithgoodreliabilityandrepeatability.WethentestedthepH-sensingcapabilityofhybridMSNcoatedwithcross-linkedP(NAS-co-OEGMA-co-NaphMA)chainbrusheswithoutloadingofguestmolecules,andtheresultsareshowninFigure4.WecanclearlyobservethatdecreasingsolutionpHintherange10-3canleadtotheoff/onswitchingoffluorescenceintensity.Uponprotonation,themorpholinemoietiescannotactaseffectivePETdonorscomparedtotheirunprotonatedstate,andthisresultsinthefluorescenceenhancementofnaphthalimidePETacceptor.AcloserexaminationofFigure4revealsthatintherangepH10-3,thefluorescenceintensitycanbeenhanced∼2timesatthemaximumemissionwavelengthof478nm.Mostimportantly,considerablefluorescenceintensitychangesoccurintherangepHLangmuir2010,26(19),15574–15579

Wanetal.5-7,whichprovestobeasuitablewindowformonitoringintracellularpHchangesanddiseasedtissues.WealsocheckedthereversibilityofpH-inducedfluorescenceintensitychanges.AsshowninFigure5,thefluorescenceintensityoftheaqueousdispersionoforganic/inorganichybridMSNcoatedwithcross-linkedP(NAS-co-OEGMA-co-NaphMA)brushesexhibitexcel-lentreversibilityuponsevenpHcyclingbetweenpH7and4.Acombinationoftheseresultsclearlyconfirmsthatthesynthesizedwater-dispersiblehybridMSNcanactassensitiveandreliablepHprobes,whichareidealforinvitroandinvivopHsensingapplications.ItshouldbenotedthatthecurrenthybridMSN-basedprobedesignemploysfluorescenceintensityforpHcali-bration,whichissubjectedtolimitationssuchasbackgroundinterference.FluorescentratiometricpHprobesbasedonthefluorescenceresonanceenergytransfer(FRET)mechanismmightbemoreideal,andfurtherworkstowardthisaspectarecurrentlyunderway.ConclusionWereportonthepreparationoffluorescentorganic/inorganichybridmesoporoussilicananoparticles(MSN)withdualcap-abilitiesofpH-probingandtunableredox-responsivereleaseofguestmolecules.Surface-initiatedRAFTpolymerizationofofN-(acryloxy)succinimide(NAS),oligo(ethyleneglycol)mono-methylethermethacrylate(OEGMA),and1,8-naphthalimide-basedpH-sensingmonomer(NaphMA)frommesoporoussilicaLangmuir2010,26(19),15574–15579Article

nanoparticlesaffordedfluorescentorganic/inorganichybridMSNcoatedwithcross-linkablepolymerbrushes,whichexhibitsgoodwaterdispersibilityandcanactasasensitivefluorescentpHprobeduetothepresenceofNaphMAmoieties.AfterloadingwithrhodamineB(RhB)asamodeldrugmolecule,P(NAS-co-OEGMA-co-NaphMA)brushesatthesurfaceofhybridMSNwerecross-linkedwitharedox-labilecross-linker,cystamine,toblocknanoporeentrances.Takingadvantageofdisulfide-con-tainingcross-linkers,thereleaserateofRhBcanbefacilelyadjustedbyaddingvaryingconcentrationsofdithiothreitol(DTT).TheincreaseofDTTconcentrationfrom0to20mMledto20-30timesenhancementofRhBreleaserate.ThereportedmultifunctionalhybridMSNaugurswellforitsapplica-tionsincontrolled-releasenanocarriers,cellandtissueimaging,andclinicaldiagnosis.Acknowledgment.ThefinancialsupportoftheNationalNaturalScientificFoundationofChina(NNSFC)Projects(20874092and51033005)andSpecializedResearchFundfortheDoctoralProgramofHigherEducation(SRFDP)isgratefullyacknowledged.SupportingInformationAvailable:Alltheexperimentalsectionincludingsyntheticproceduresandspectroscopic/analy-ticaldataof1HNMR,GPC,XRD,BET,FT-IR,UV-visabsorption,andspectrofluorometry.ThismaterialisavailablefreeofchargeviatheInternetathttp://pubs.acs.org.

DOI:10.1021/la102148x15579