Thermoplasmonic ssDNA Dynamic Release from Gold Nanoparticles Examined with Advanced Fluorescence Microscopy

Plasmon excitation of spherical gold nanoparticles carrying a fluorescent labeled 30 bp dsDNA cargo, with one chain covalently attached through two S–Au bonds to the surface, results in release of the complementary strand as ssDNA that can be examined in situ using high-resolution fluorescence microscopy. The release is dependent on the total energy delivered, but not the rate of delivery, an important property for plasmonic applications in medicine, sensors, and plasmon-induced PCR

Study of solvent-conjugated polymer interactions by polarized spectroscopy: MEH-PPV and Poly(9,9 '-dioctylfluorene-2,7-diyl)

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Absorption, emission, and anisotropy measurements were performed on poly-[2-methoxy-5(2'-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) and poly-(9,9'-dioctylfluorene-2,7-diyl) (PF) solutions of various solvents, and in thin films deposited from them. The good correlation of MEH-PPV absorption and emission energy with Hildebrandt's dispersive parameter indicate that dispersive forces regulate the effective extent of the luminophore. The excitation and the emission spectra of alpha and beta chains can be distinguished in PF solutions using the steady-state anisotropy. PF films show greater memory effect from the solutions from which they were Spun than MEH-PPV. Anisotropy of MEH-PPV is very low, both in solutions and in films reflecting efficient energy migration. Anisotropy of PF in solutions and films demonstrates great differences in energy transfer efficiency within the alpha and beta phases, while there is no energy transfer between these chain conformations. (C) 2009 Published by Elsevier B.V.1303415423Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)FAEPEX/UnicampCONICET (Consejo Nacional de Investigaciones Cientificas y Tecnicas, Argentina) [PIP 5470]ANPCyT, Argentina [PICT 10621]UBA [X086][CAPGBA03/02]Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)CONICET (Consejo Nacional de Investigaciones Cientificas y Tecnicas, Argentina) [PIP 5470]ANPCyT, Argentina [PICT 10621]UBA [X086][CAPGBA03/02

Fluorescent polymer coatings with tuneable sensitive range for remote temperature sensing

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Polymer films of poly(vinyl alcohol) containing the fluorescent dyes 4-aminophthalimide (AP) or 6-propiony1-2-dimethylamino-naphthalene (Prodan) are used as temperature-sensitive fluorescent coatings for remote temperature sensing. Temperature can be obtained by a two-wavelength ratiometric-based emission intensity measurement. The coatings are sensitive in a 100 K temperature range that can be tuned by polymer-solute interactions. The usable range is 200-300 K for AP and 280-380 K for Prodan. (C) 2013 Elsevier B.V. All rights reserved.1161316ANPCyT, UBACONICET (Argentina)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Relaxations in poly(vinyl alcohol) and in poly(vinyl acetate) detected by fluorescence emission of 4-aminophthalimide and Prodan

Steady-state and time-resolved emission spectroscopy (TRES) of the medium-sensitive probes 4-aminophthalimide (4-AP) and 6-propionyl-2-(dimethylamino)naphthalene (Prodan) were performed at 77 and 298 K in vacuum-sealed thin films of poly(vinyl alcohol) (PVA) and poly(vinyl acetate) (PVAc). The two probes show similar red-edge effect in steady state emission and a red shift with time in TRES in PVA. In PVAc the red shifts are much smaller and the spectral shift for 4-AP is slower. 4-AP locates in highly polar environments in PVA, where H-bond interaction with the polymer is important. Prodan locates in less polar environments, as evidenced by the position of the emission maximum with respect to reference solvents. Consequently, the observed monoexponential spectral red shift with time of 4-AP in PVA and in PVAc is attributed to relaxation of the interaction of the probe with the hydroxy and acetate moieties, respectively. The more intense interaction of the lighter -OH moiety with the probes explains the greater and faster spectral shift observed in PVA compared to PVAc. The lifetime of this monoexponential spectral shift is independent of temperature in PVA and takes place with a highly negative activation entropy. This fact is attributed to a collective rearrangement of -OH groups to better interact with the excited state. This relaxation nevertheless does not account for the complete accommodation of the excited state. Prodan shows a linear variation of the spectral shift with time that can be explained by microheterogeneity. In PVA, the width at half-maximum of the emission spectra does not change with time for Prodan and it decays with a lifetime similar to the lifetime of the spectral shift in the case of 4-AP. The differences in the behavior of the probes are attributed to their different average location in the polymer matrix.10933161801618

Novel kinetic model in amorphous polymers. Spiropyran-merocyanine system revisited

A kinetic model for the description of non-monoexponential decay of unimolecular reactions in amorphous polymers is developed. The thermal decay of the merocyanine (MC) form of 1,3',3'-trimethyl-6-nitrospiro-[2H-1-benzopyran-2,2'-indoline] (spiropyran, SP) in poly(alkyl methacrylates) is taken as an example. The model assumes that the time dependent first-order rate constant describing the decay relaxes from an initial value k(0) to a completely relaxed value k(infinity) with a relaxation time tau(m) that depends on the matrix. A rate equation similar to the one provided by this model is found in fluorescence quenching either in micelles or in the picosecond range in solution. The fit of the temperature dependent decays of MC to SP with this model is as good as or better than the one obtained by other models such as the sum of exponential terms or the stretched exponential equation. The simple relaxation picture is unable to account for the decay at temperatures far below the glass transition temperature of the polymer. In this range, the average values of rates, represented by k(0), k(infinity), and tau(m), poorly describe the real distribution of them. The values of k(0), k(infinity), and tau(m) for MC decay show an Arrhenius behavior in the polymers studied.101397680768