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1、,Energy Transfer Mediated Fluorescence from Blended Conjugated Polymer Nanoparticles,Changfeng Wu,Hongshang Peng,Yunfei Jiang,and Jason McNeill*,2,Abstract,Nanoparticles consisting of a derivative of the blue-emitting conjugated polymer polyfluorene doped with green-,yellow-,and red-emitting conjuga
2、ted polymers were prepared by a reprecipitation method.The nanoparticles can be described as a system of densely packed chromophores that exhibit efficient energy transfer from the host to the dopant polymers.,3,Abstract,Fluorescence quenching analysis of the host polymer as a function of the dopant
3、 concentration indicates that one energy acceptor molecule can effectively quench 90%of the fluorescence of a nanoparticle consisting of 100-200 host conjugated polymer molecules.A nanoparticle energy transfer model was developed that successfully describes the quenching behavior of a small number o
4、f highly efficient energy acceptors per nanoparticle.,4,Abstract,The fluorescence brightness of the blended polymer nanoparticles was determined to be much higher than that of inorganic quantum dots and dye-loaded silica particles of similar dimensions.The combination of high fluorescence brightness
5、 and tunable fluorescence of these blended nanoparticles is promising for ultrasensitive fluorescence-based assays.,5,Contents,6,1.Introduction,Highly fluorescent nanoparticles have attracted much attention due to a variety of fluorescence-based applications such as biosensing,imaging,and high-throu
6、gh put assays.Conjugated polymers are known to possess high absorption coefficients and high fluorescence efficiency,which have led to a wide range of applications in optoelectronic thin film devices.However,the use of conjugated polymer nanoparticles in fluorescence labeling is still a largely unex
7、plored area.,7,1.Introduction,Energy transfer in nanoscale systems has recently been demonstrated as the basis of molecular beacons for efficient biomolecule detection.Here we report on energy transfer mediated fluorescence from conjugated polymer nanoparticles consisting of polyfluorene(PF)doped wi
8、th three different conjugated polymer acceptors.,8,2.Experimental Section,2.1 Materials,2.2 Nanoparticle Preparation,2.3 Characterization Methods,9,2.1.Materials,HostPF：poly(9,9-dihexylfluorenyl-2,7-diyl)(MW 55 000,polydispersity 2.7)DopantsPFPV：poly9,9-dioctyl-2,7-divinylenefluorenylene-alt-co-2-me
9、thoxy-5-(2-ethylhexyloxy)-1,4-phenylene(MW 270 000,polydispersity 2.7),PFBT：poly(9,9-dioctylfluorenyl-2,7-diyl)-co-(1,4-benzo-2,1,3-thiadiazole)(MW 10 000,polydispersity 1.7)MEH-PPV：poly2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene(MW 200 000,polydispersity7.0)THF：Tetrahydrofuran(anhydrous,99.
10、9%),10,2.2.Nanoparticle Preparation,THF,+polymer,inert atmosphere,stirring overnight,filtered,c=40 ppm,homogeneous solutions,+dopant(0 to 10 wt%),diluted,stirred,Preparation of the aqueous dispersion of blended conjugated polymer nanoparticles,11,2.2.Nanoparticle Preparation,8 mL of deionizedwater,n
11、anoparticle dispersions,suspension,2 mL of solution mixture,added quickly,sonicating,filtered,partial vacuum evaporation,The resulting nanoparticle dispersions are clear and stable for months with no signs of aggregation.,12,2.3.Characterization Methods,Morphology and size distribution of the polyme
12、r blend nanoparticles were characterized by atomic force microscopy(AFM).The UV-vis absorption spectra were recorded with a Shimadzu UV-2101PC scanning spectrophotometer,using 1 cm quartz cuvettes.Fluorescence spectra were collected with a commercial fluorometer(Quantamaster,PTI,Inc.),using a 1 cm q
13、uartz cuvette.,13,3.Results and Discussion,Diagram,14,3.1.Nanoparticle Size and Morphology,(a)Chemical structures of the conjugated polymers,15,3.1.Nanoparticle Size and Morphology,(b)a representative AFM image of blend nanoparticles dispersed on silicon substrate,(c)histogram of particle height dat
14、a taken from AFM image,16,3.2.Optical Properties,(d)photograph of fluorescence emission from aqueous suspensions of the blend nanoparticles taken under a UV lamp(365 nm).,17,3.2.Optical Properties,Figure 2.(Left)Normalized absorption and fluorescence emission spectra of conjugated polymers PF,PFPV,P
15、FBT,and MEH-PPV in THF solution.(Right)Normalized absorption(dashed)and fluorescence excitation and emission spectra(solid)of pure PF and polymer blend nanoparticles.,415,550,535,500,430,18,3.2.Optical Properties,Figure 3.(Left)Concentration-dependent fluorescence spectra of polymer blend nanopartic
16、les under 375 nm excitation.(Right)Fluorescence intensity change of PF host and dopant polymers as a function of dopant concentration in blend nanoparticles.,19,3.3.Nanoparticle Energy Transfer Model,The dependence of host polymer fluorescence intensity on the concentration of dopant(quencher)was mo
17、deled by using the Stern-Volmer relation,which can be expressed as：,F0-fluorescence intensities in the absence of quencherF-fluorescence intensities in the presence of quencherKSV-Stern-Volmerquenching constantQ-the concentration of the quencher,F0/F=1=KsvQ,20,kr-radiative rates of the host knr-nonr
18、adiative rates of the host ket-energy transfer rate of a single quencher n-the number of quenchers present in the nanoparticle,(F/F0)-relative fluorescence intensity q-quenching efficiency per quencher molecule,n-the average number of donor molecules per nanoparticle.,3.3.Nanoparticle Energy Transfe
19、r Model,21,Figure 4.Fluorescence quenching of PF donor versus molar fraction of quenchers in polymer blend nanoparticles.The scattered squares are experimental data,while the black dashed curves are model results given by eq 5.The solid lines represent linear Stern-Volmer plots of PF fluorescence qu
20、enched by three quenchers in the low concentration range.,3.3.Nanoparticle Energy Transfer Model,22,4.Conclusions,PF nanoparticles doped with PFPV,PFBT,and MEH-PPV,respectively,were prepared by a reprecipitation method.Salient features of the nanoparticles include their high fluorescence brightness
21、and suitability for fluorescence multiplexing applications.In some cases,the dependence of nanoparticle fluorescence on composition was found to deviate substantially from the Stern-Volmer relation.,23,4.Conclusions,Analyses by both Stern-Volmer relation and the nanoparticle energy transfer model reveal highly efficient energy transfer between the host and the guest molecules.Both models indicate that approximately 100 or more host molecules are quenched by a single dopant molecule.,24,THANK YOU!,
