Página 1 dos resultados de 1862 itens digitais encontrados em 0.003 segundos

Photoexpansion and photobleaching effects in oxysulfide thin films of the GeS2+Ga2O3 system

Mendes, A. C.; Maia, L. J. Q.; Messaddeq, S. H.; Messaddeq, Y.; Ribeiro, S. J. L.; Li, M. Siu
Fonte: Elsevier B.V. Publicador: Elsevier B.V.
Tipo: Artigo de Revista Científica Formato: 4381-4386
ENG
Relevância na Pesquisa
36.881772%
Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Processo FAPESP: 05/58396-0; Oxysulfide systems undergo structural transformations upon illumination with laser light of near bandgap energy, as well as chalcogenide materials (glasses and films). In this paper, photoinduced effects such as photoexpansion and photobleaching were observed in GeS2+Ga2O3 (GGSO) films synthesized by electron beam evaporation. A surface expansion of the thin films and a shift to shorter wavelengths of the optical absorption edge were observed as a result of UV laser irradiation (wavelength of 351 nm) and they are dependent on laser power density, exposure time and film composition. These parameters were varied to evaluate and enhance the observed effects. In addition, the irradiated GGSO samples exhibited a decrease in refractive index, measured with a prism-coupling technique, which makes these films suitable candidates for applications as gratings and waveguides in integrated optics. (C) 2011 Elsevier B.V. All rights reserved.

Dynamics and interactions of nuclear proteins revealed by quantitative photobleaching microscopy

Rino, José, 1976-
Fonte: Universidade de Lisboa Publicador: Universidade de Lisboa
Tipo: Tese de Doutorado
Publicado em //2007 ENG
Relevância na Pesquisa
27.248945%
Tese de doutoramento em Biofísica (Biofísica), apresentada à Universidade de Lisboa através da Faculdade de Ciências, 2007; The nucleus is a complex cellular organelle, exhibiting a high degree of organization and also a highly dynamic nature. Live cell imaging using fluorescent proteins (FPs) as molecular tags and photobleaching techniques have been essential in revealing the dynamic nature of the cell nucleus. In this thesis, these tools were used to study molecular dynamics and interactions inside this cellular compartment. Fluorescence Recovery After Photobleaching (FRAP) and Fluorescence Loss In Photobleaching (FLIP) were used to analyze the kinetic behavior of spliceosome components SmE, U2AF65, U2AF35, SF1 and SC35 in the nucleus of living cells. The recruitment mechanism of splicing factors (SFs) to the sites of transcription is still poorly understood. Our results rule out the hypothesis that a transcription specific signal recruits SFs from the speckles. They also suggest the formation of multi-protein complexes distinct from the spliceosome. The existence of these complexes was confirmed by Fluorescence Resonance Energy Transfer (FRET) techniques, which revealed that SFs could interact with each other even in the absence of active splicing. A novel U2AF65 self-interaction was also detected...

Photobleaching recovery and anisotropy decay of green fluorescent protein GFP-S65T in solution and cells: cytoplasmic viscosity probed by green fluorescent protein translational and rotational diffusion.

Swaminathan, R; Hoang, C P; Verkman, A S
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /04/1997 EN
Relevância na Pesquisa
27.1954%
The green fluorescent protein (GFP) was used as a noninvasive probe to quantify the rheological properties of cell cytoplasm. GFP mutant S65T was purified from recombinant bacteria for solution studies, and expressed in CHO cell cytoplasm. GFP-S65T was brightly fluorescent in solution (lambda ex 492 nm, lambda em 509 nm) with a lifetime of 2.9 ns and a rotational correlation time (tc) of 20 ns. Recovery of GFP fluorescence after photobleaching was complete with a half-time (t1/2) in aqueous saline of 30 +/- 2 ms (5-micron diameter spot), giving a diffusion coefficient of 8.7 x 10(-7) cm2/s. The t1/2 was proportional to solution viscosity and was dependent on spot diameter. In contrast to fluorescein. GFP photobleaching efficiency was not affected by solution O2 content, triplet state quenchers, singlet oxygen scavengers, and general radical quenchers. In solutions of higher viscosity, an additional, rapid GFP recovery process was detected and ascribed to reversible photobleaching. The t1/2 for reversible photobleaching was 1.5-5.5 ms (relative viscosity 5-250), was independent of spot diameter, and was unaffected by O2 or quenchers. In cell cytoplasm, time-resolved microfluorimetry indicated a GFP lifetime of 2.6 ns and a tc of 36 +/- 3 ns...

Influence of the triplet excited state on the photobleaching kinetics of fluorescein in microscopy.

Song, L; Varma, C A; Verhoeven, J W; Tanke, H J
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /06/1996 EN
Relevância na Pesquisa
27.1954%
The investigation in this report aimed at providing photophysical evidence that the long-lived triplet excited state plays an important role in the non-single-exponential photobleaching kinetics of fluorescein in microscopy. Experiments demonstrated that a thiol-containing reducing agent, mercaptoethylamine (MEA or cysteamine), was the most effective, among other commonly known radical quenchers or singlet oxygen scavengers, in suppressing photobleaching of fluorescein while not reducing the fluorescence quantum yield. The protective effect against photobleaching of fluorescein in the bound state was also found in microscopy. The antibleaching effect of MEA let to a series of experiments using time-delayed fluorescence spectroscopy and nanosecond laser flash photolysis. The combined results showed that MEA directly quenched the triplet excited state and the semioxidized radical form of fluorescein without affecting the singlet excited state. The triplet lifetime of fluorescein was reduced upon adding MEA. It demonstrated that photobleaching of fluorescein in microscopy is related to the accumulation of the long-lived triplet excited state of fluorescein and that by quenching the triplet excited state and the semioxidized form of fluorescein to restore the dye molecules to the singlet ground state...

Effects of second order photobleaching on recovered diffusion parameters from fluorescence photobleaching recovery

Bjarneson, D. W.; Petersen, N. O.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /11/1991 EN
Relevância na Pesquisa
27.248945%
In the original theoretical development of fluorescence photobleaching recovery with circular or Gaussian laser intensity profiles (Axelrod et al., 1976, Biophys. J.) the bleaching process is assumed to obey first order kinetics in the fluorescent probe. While this is reasonable in most cases where oxygen participates in the photolysis reaction, some processes may obey second order kinetics in the fluorophore concentration due to dimerization. Accordingly, we present here an analysis of the fluorescence recovery when the photobleaching process is taken to be second order in the probe. Analytical solutions for small bleaching levels indicate that the fluorescence recovery curve is very similar to that measured following a bleaching process first order in the probe. Numerical solutions for moderate bleaching levels show that the recovery is qualitatively similar, but quantitatively different. Because the shape of the recovery curve provides no evidence as to the order of photobleaching, we recommend continued use of the previous theoretical analysis. However, it must be borne in mind that the diffusion coefficient is increasingly underestimated as the extent of photobleaching is increased. The true diffusion coefficient is obtained in the limit of small levels of photobleaching. Estimates of the fractional recovery are not affected by this approach.

Photobleaching kinetics of fluorescein in quantitative fluorescence microscopy.

Song, L; Hennink, E J; Young, I T; Tanke, H J
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /06/1995 EN
Relevância na Pesquisa
27.248945%
An investigation on the photobleaching behavior of fluorescein in microscopy was carried out through a systematic analysis of photobleaching mechanisms. The individual photochemical reactions of fluorescein were incorporated into a theoretical analysis and mathematical simulation to study the photochemical processes leading to photobleaching of fluorescein in microscopy. The photobleaching behavior of free and bound fluorescein has also been investigated by experimental means. Both the theoretical simulation and experimental data show that photobleaching of fluorescein in microscopy is, in general, not a single-exponential process. The simulation suggests that the non-single-exponential behavior is caused by the oxygen-independent, proximity-induced triplet-triplet or triplet-ground state dye reactions of bound fluorescein in microscopy. The single-exponential process is a special case of photobleaching behavior when the reactions between the triplet dye and molecular oxygen are dominant.

Photobleaching in two-photon excitation microscopy.

Patterson, G H; Piston, D W
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /04/2000 EN
Relevância na Pesquisa
27.248945%
The intensity-squared dependence of two-photon excitation in laser scanning microscopy restricts excitation to the focal plane and leads to decreased photobleaching in thick samples. However, the high photon flux used in these experiments can potentially lead to higher-order photon interactions within the focal volume. The excitation power dependence of the fluorescence intensity and the photobleaching rate of thin fluorescence samples ( approximately 1 microm) were examined under one- and two-photon excitation. As expected, log-log plots of excitation power versus the fluorescence intensity and photobleaching rate for one-photon excitation of fluorescein increased with a slope of approximately 1. A similar plot of the fluorescence intensity versus two-photon excitation power increased with a slope of approximately 2. However, the two-photon photobleaching rate increased with a slope > or =3, indicating the presence of higher-order photon interactions. Similar experiments on Indo-1, NADH, and aminocoumarin produced similar results and suggest that this higher-order photobleaching is common in two-photon excitation microscopy. As a consequence, the use of multi-photon excitation microscopy to study thin samples may be limited by increased photobleaching.

Continuous Photobleaching in Vesicles and Living Cells: A Measure of Diffusion and Compartmentation

Delon, A.; Usson, Y.; Derouard, J.; Biben, T.; Souchier, C.
Fonte: Biophysical Society Publicador: Biophysical Society
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
27.32454%
We present a comprehensive and analytical treatment of continuous photobleaching in a compartment, under single photon excitation. In the very short time regime (t < 0.1 ms), the diffusion does not play any role. After a transition (or short time regime), one enters in the long time regime (t > 0.1–5 s), for which the diffusion and the photobleaching balance each other. In this long time regime, the diffusion is either fast (i.e., the photobleaching probability of a molecule diffusing through the laser beam is low) so that the photobleaching rate is independent of the diffusion constant and dependent only of the laser power, or the diffusion is slow (i.e., the photobleaching probability is high) and the photobleaching rate is mainly dependent on the diffusion constant. We illustrate our theory by using giant unilamellar vesicles ranging from ∼10 to 100 μm in diameter, loaded with molecules of various diffusion constants (from 20 to 300 μm2/s) and various photobleaching cross sections, illuminated under laser powers between 3 and 100 μW. We also demonstrated that information about compartmentation can be obtained by this method in living cells expressing enhanced green fluorescent proteins or that were loaded with small FITC-dextrans. Our quantitative approach shows that molecules freely diffusing in a cellular compartment do experience a continuous photobleaching. We provide a generic theoretical framework that should be taken into account when studying...

Decreasing photobleaching by silver island films: application to muscle⋆

Muthu, P.; Gryczynski, I.; Gryczynski, Z.; Talent, J.; Akopova, I.; Jain, K.; Borejdo, J.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
27.352214%
Recently it has become possible to study interactions between proteins at the level of single molecules. This requires collecting data from an extremely small volume, small enough to contain one molecule—typically of the order of attoliters (10−18 L). Collection of data from such a small volume with sufficiently high signal-to-noise ratio requires that the rate of photon detection per molecule be high. This calls for a large illuminating light flux, which in turn leads to rapid photobleaching of the fluorophores that are labeling the proteins. To decrease photobleaching, we measured fluorescence from a sample placed on coverslips coated with silver island films (SIF). SIF reduce photobleaching because they enhance fluorescence brightness and significantly decrease fluorescence lifetime. Increase in the brightness effectively decreases photobleaching because illumination can be attenuated to obtain the same fluorescence intensity. Decrease of lifetime decreases photobleaching because short lifetime minimizes the probability of oxygen attack while the fluorophore is in the excited state. The decrease of photobleaching was demonstrated in skeletal muscle. Myofibrils were labeled lightly with rhodamine–phalloidin, placed on coverslips coated with SIF...

Photobleaching Pathways in Single Molecule FRET Experiments

Kong, Xiangxu; Nir, Eyal; Hamadani, Kambiz; Weiss, Shimon
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
27.375352%
In order to acquire accurate structural and dynamical information on complex biomolecular machines using single-molecule fluorescence resonance energy transfer (sm-FRET), a large flux of donor and acceptor photons are needed. To achieve such fluxes one may use higher laser excitation intensity, however this induces increased rates of photobleaching. Anti-oxidants additives have been extensively used for reducing acceptor’s photobleaching. Here we focus on deciphering the initial step along the photobleaching pathway. Utilizing an array of recently-developed single molecule and ensemble spectroscopies, and doubly-labeled Acyl-CoA binding protein and double-stranded DNA as model systems, we study these photobleaching pathways which place fundamental limitations on sm-FRET experiments. We find that: (i) acceptor photobleaching scales with FRET efficiency; (ii) acceptor photobleaching is enhanced under picosecond pulsed (vs. continuous wave) excitation; and (iii) acceptor photobleaching scales with the intensity of only the short wavelength (donor) excitation laser. We infer from these findings that the main pathway for acceptor’s photobleaching is through absorption of a short wavelength photon from the acceptor’s first excited singlet state and that donor’s photobleaching is usually not a concern. We conclude by suggesting using short pulses for donor excitation...

Circumvention of Fluorophore Photobleaching in Fluorescence Fluctuation Experiments: a Beam Scanning Approach

Satsoura, Dmitri; Leber, Brian; Andrews, David W.; Fradin, Cécile
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 23/04/2007 EN
Relevância na Pesquisa
27.248945%
Photobleaching is a fluorophore-damaging process that commonly afflicts single-molecule fluorescence studies. It becomes an especially severe problem in fluorescence fluctuation experiments when studying slowly diffusing particles. One way to circumvent this problem is to use beam scanning to decrease the residence time of the fluorophores in the excitation volume. We report a systematic study of the effects of circular beam scanning on the photobleaching of fluorescent particles as observed in single-photon excitation fluorescence fluctuation experiments. We start by deriving a simple expression relating the average detected fluorescence to the photobleaching cross section of the fluorophores. We then perform numerical calculations of the spatial distribution of fluorescent particles in order to understand under which conditions beam scanning can prevent the formation of a photobleaching hole. To support these predictions, we show experimental results obtained for large unilamellar vesicles containing a small amount of the fluorescent lipophilic tracer DiD. We establish the required scanning radius and frequency range in order to obtain sufficient reduction of the photobleaching effect for that system. From the detected increase in fluorescence upon increase in scanning speed...

Fluence Rate-Dependent Photobleaching of Intratumorally-Administered Pc 4 Does Not Predict Tumor Growth Delay

Baran, Timothy M.; Foster, Thomas H.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
27.248945%
We examined effects of fluence rate on the photobleaching of the photosensitizer Pc 4 during photodynamic therapy (PDT) and the relationship between photobleaching and tumor response to PDT. BALB/c mice with intradermal EMT6 tumors were given 0.03 mg/kg Pc 4 by intratumor injection and irradiated at 667 nm with an irradiance of 50 or 150 mW/cm2 to a fluence of 100 J/cm2. While no cures were attained, significant tumor growth delay was demonstrated at both irradiances compared to drug-only controls. There was no significant difference in tumor responses to these two irradiances (p = 0.857). Fluorescence spectroscopy was used to monitor the bleaching of Pc 4 during irradiation, with more rapid bleaching with respect to fluence shown at the higher irradiance. No significant correlation was found between fluorescence photobleaching and tumor regrowth for the data interpreted as a whole. Within each treatment group, weak associations between photobleaching and outcome were observed. In the 50 mW/cm2 group, enhanced photobleaching was associated with prolonged growth delay (p = 0.188), while at 150 mW/cm2 this trend was reversed (p = 0.308). Thus, it appears that Pc 4 photobleaching is not a strong predictor of individual tumor response to Pc4-PDT under these treatment conditions.

Thermal Acclimation of the Symbiotic Alga Symbiodinium spp. Alleviates Photobleaching under Heat Stress1[W][OA]

Takahashi, Shunichi; Yoshioka-Nishimura, Miho; Nanba, Daisuke; Badger, Murray R.
Fonte: American Society of Plant Biologists Publicador: American Society of Plant Biologists
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
27.248945%
A moderate increase in seawater temperature causes coral bleaching, at least partially through photobleaching of the symbiotic algae Symbiodinium spp. Photobleaching of Symbiodinium spp. is primarily associated with the loss of light-harvesting proteins of photosystem II (PSII) and follows the inactivation of PSII under heat stress. Here, we examined the effect of increased growth temperature on the change in sensitivity of Symbiodinium spp. PSII inactivation and photobleaching under heat stress. When Symbiodinium spp. cells were grown at 25°C and 30°C, the thermal tolerance of PSII, measured by the thermal stability of the maximum quantum yield of PSII in darkness, was commonly enhanced in all six Symbiodinium spp. tested. In Symbiodinium sp. CCMP827, it took 6 h to acquire the maximum PSII thermal tolerance after transfer from 25°C to 30°C. The effect of increased growth temperature on the thermal tolerance of PSII was completely abolished by chloramphenicol, indicating that the acclimation mechanism of PSII is associated with the de novo synthesis of proteins. When CCMP827 cells were exposed to light at temperature ranging from 25°C to 35°C, the sensitivity of cells to both high temperature-induced photoinhibition and photobleaching was ameliorated by increased growth temperatures. These results demonstrate that thermal acclimation of Symbiodinium spp. helps to improve the thermal tolerance of PSII...

Photobleaching Response of Different Sources of Chromophoric Dissolved Organic Matter Exposed to Natural Solar Radiation Using Absorption and Excitation–Emission Matrix Spectra

Zhang, Yunlin; Liu, Xiaohan; Osburn, Christopher L.; Wang, Mingzhu; Qin, Boqiang; Zhou, Yongqiang
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Publicado em 25/10/2013 EN
Relevância na Pesquisa
27.248945%
CDOM biogeochemical cycle is driven by several physical and biological processes such as river input, biogeneration and photobleaching that act as primary sinks and sources of CDOM. Watershed-derived allochthonous (WDA) and phytoplankton-derived autochthonous (PDA) CDOM were exposed to 9 days of natural solar radiation to assess the photobleaching response of different CDOM sources, using absorption and fluorescence (excitation-emission matrix) spectroscopy. Our results showed a marked decrease in total dissolved nitrogen (TDN) concentration under natural sunlight exposure for both WDA and PDA CDOM, indicating photoproduction of ammonium from TDN. In contrast, photobleaching caused a marked increase in total dissolved phosphorus (TDP) concentration for both WDA and PDA CDOM. Thus TDN∶TDP ratios decreased significantly both for WDA and PDA CDOM, which partially explained the seasonal dynamic of TDN∶TDP ratio in Lake Taihu. Photobleaching rate of CDOM absorption a(254), was 0.032 m/MJ for WDA CDOM and 0.051 m/MJ for PDA CDOM from days 0–9, indicating that phototransformations were initially more rapid for the newly produced CDOM from phytoplankton than for the river CDOM. Extrapolation of these values to the field indicated that 3.9%–5.1% CDOM at the water surface was photobleached and mineralized every day in summer in Lake Taihu. Photobleaching caused the increase of spectral slope...

Multiphoton fluorescence recovery after photobleaching : advancements for novel in vivo applications

Sullivan, Kelley Diane (1978 - ); Brown, Edward B.
Fonte: University of Rochester Publicador: University of Rochester
Tipo: Tese de Doutorado Formato: Number of Pages:xviii, 137 leaves
ENG
Relevância na Pesquisa
27.290852%
Thesis (Ph. D.)--University of Rochester. Dept. of Physics and Astronomy, 2010.; Multiphoton fluorescence recovery after photobleaching (MP-FRAP) is a laser microscopy technique used to probe the transport properties of macromolecules in biological systems. MP-FRAP utilizes two-photon fluorescence and photobleaching to produce a three-dimensionally resolved diffusion coefficient for an ensemble of molecules in the region of the two-photon focal volume. This thesis describes two fundamental improvements to the MP-FRAP technique, which are vital steps to enable MP-FRAP to be applied to the complex in vivo environment. In Chapter 1, we lay the groundwork for our discussion of these advancements by introducing the MP-FRAP technique and the physics upon which it is based. We begin with a description of fluorescence and diffusion and discuss their importance in biomedical research. Next, we describe how two-photon fluorescence and photobleaching are applied to a diffusing system to measure the diffusion coefficient via fluorescence recovery after photobleaching (FRAP). Then, we take the reader through the evolution of FRAP, which leads to the application of twophoton fluorescence and photobleaching to produce MP-FRAP. Along the way...

Resonant Scanning with Large Field of View Reduces Photobleaching and Enhances Fluorescence Yield in STED Microscopy

Wu, Yong; Wu, Xundong; Lu, Rong; Zhang, Jin; Toro, Ligia; Stefani, Enrico
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Artigo de Revista Científica
Publicado em 01/10/2015 EN
Relevância na Pesquisa
27.248945%
Photobleaching is a major limitation of superresolution Stimulated Depletion Emission (STED) microscopy. Fast scanning has long been considered an effective means to reduce photobleaching in fluorescence microscopy, but a careful quantitative study of this issue is missing. In this paper, we show that the photobleaching rate in STED microscopy can be slowed down and the fluorescence yield be enhanced by scanning with high speed, enabled by using large field of view in a custom-built resonant-scanning STED microscope. The effect of scanning speed on photobleaching and fluorescence yield is more remarkable at higher levels of depletion laser irradiance, and virtually disappears in conventional confocal microscopy. With ≥6 GW∙cm−2 depletion irradiance, we were able to extend the fluorophore survival time of Atto 647N and Abberior STAR 635P by ~80% with 8-fold wider field of view. We confirm that STED Photobleaching is primarily caused by the depletion light acting upon the excited fluorophores. Experimental data agree with a theoretical model. Our results encourage further increasing the linear scanning speed for photobleaching reduction in STED microscopy.

Digital imaging fluorescence microscopy: spatial heterogeneity of photobleaching rate constants in individual cells

Fonte: The Rockefeller University Press Publicador: The Rockefeller University Press
Tipo: Artigo de Revista Científica
Publicado em 01/04/1985 EN
Relevância na Pesquisa
27.375352%
Photobleaching and related photochemical processes are recognized experimental barriers to quantification of fluorescence by microscopy. We have measured the kinetics of photobleaching of fluorophores in living and fixed cells and in microemulsions, and have demonstrated the spatial variability of these processes within individual cells. An inverted fluorescence microscope and a high-sensitivity camera, together with high-speed data acquisition by a computer-controlled image processor, have been used to control precisely exposure time to excitation light and to record images. To improve the signal-to-noise ratio, 32 digital images were integrated. After correction for spatial variations in camera sensitivity and background fluorescence, the images of the relative fluorescence intensities for 0.065 micron2 areas in the object plane were obtained. To evaluate photobleaching objectively, an algorithm was developed to fit a three-parameter exponential equation to 20 images recorded from the same microscope field as a function of illumination time. The results of this analysis demonstrated that the photobleaching process followed first-order reaction kinetics with rate constants that were spatially heterogeneous and varied, within the same cell...

Resonant Scanning with Large Field of View Reduces Photobleaching and Enhances Fluorescence Yield in STED Microscopy

Wu, Yong; Wu, Xundong; Lu, Rong; Zhang, Jin; Toro, Ligia; Stefani, Enrico
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.248945%
Photobleaching is a major limitation of superresolution Stimulated Depletion Emission (STED) microscopy. Fast scanning has long been considered an effective means to reduce photobleaching in fluorescence microscopy, but a careful quantitative study of this issue is missing. In this paper, we show that the photobleaching rate in STED microscopy is slowed down and fluorescence yield is enhanced by scanning with high linear speed, enabled by the large field of view in our custom-built resonant-scanning STED microscope. The effect of scanning speed on photobleaching and fluorescence yield is more remarkable at higher levels of depletion laser irradiance, and virtually disappears in conventional confocal microscopy. With a depletion irradiance of >0.2 GW$\cdot$cm$^{-2}$ (time average), we were able to extend the fluorescence survival time of the Atto 647N dye by ~80% with an 8-fold wider field of view. We confirm that STED Photobleaching is primarily caused by the depletion light acting upon the excited fluorophores. Experimental data agree with a theoretical model. Our results encourage further increasing linear scanning speed for photobleaching reduction in STED microscopy.; Comment: 9 figures, 2 tables. With supplementary information (8 figures)

Selective photobleaching of chlorophylls and carotenoids in Photosystem I particles under high-light treatment

Andreeva, Atanaska; Abarova, Silvia; Stoitchkovaa, Katerina; Picorel Castaño, Rafael; Velitchkova, Maya Y.
Fonte: Blackwell Publishing Publicador: Blackwell Publishing
Tipo: Artículo Formato: 267815 bytes; application/pdf
ENG
Relevância na Pesquisa
36.881772%
The definitive version is available at: www.blackwell-synergy.com; Photosystem I particles (PSI-200) isolated from spinach leaves were studied by means of absorbance, 77K fluorescence, and resonance Raman spectroscopy. The aim was to obtain better insight into the changes of in the pigment spectral properties of pigments molecules in those Photosystem I particles during prolonged exposure to high-light intensities and to reveal the involvement of these pigments in the photoprotection of the Photosystem I. particles. During prolonged exposure to high-light intensities of spinach Photosystem I particles, a loss of a significant amount of photosynthetic pigments was observed. It was shown that various pigments exhibited different susceptibility to photodamage. effect. In addition to bleaching of chlorophyll a, bleaching of carotenoids was also clearly observed. Resonance Raman technique allowed us to recognize the type and conformation of photobleached carotenoid molecules. Raman data revealed a nearly full photobleaching of the long-wavelength lutein molecules. The observed similar bleaching rate of the lutein molecules and the most red-shifted long-wavelength chlorophyll a absorbing pigments, located in the antenna membrane protein Lcha4...

Electronic properties of chemically produced silver clusters: Photobleaching studies

Hailstone, Richard; Tan, Ji
Fonte: The Society for Imaging Science and Technology (IS&T) Publicador: The Society for Imaging Science and Technology (IS&T)
Tipo: Artigo de Revista Científica
EN_US
Relevância na Pesquisa
37.12458%
Chemically produced silver clusters lead to a 476 nm peak in the diffuse reflectance spectra (DRS) of AgBr emulsions. Earlier photobleaching studies have shown that this peak can be resolved into two component peaks-one at 474 nm which photobleaches, and a less intense one at 482 nm that does not. The 474 nm peak has been assigned to hole removing silver clusters. This interpretation has been questioned since photoproduced silver clusters, which are obviously electron trapping, are also known to photobleach (solarization). This possibility was examined with photoproduced silver clusters and photobleach conditions which were identical to those used for the earlier photobleach study. Such clusters are found to photobleach, but not to the extent that would explain the observed photobleaching of the 474 nm DRS peak. In the presence of a modest amount of hole removing silver clusters provided by reduction sensitization, the photoproduced silver clusters underwent minimal photobleaching. These results support the earlier assignment of the 474 nm DRS peak to hole removing silver clusters.; This article may be accessed on the publisher's website (additional fees may apply) at: http://www.imaging.org/store/epub.cfm?abstrid=6922