SwePub - sökning: WFRF:(Camacho Rafael)

Numrering	Referens	Omslagsbild	Hitta
1.	Louis, Boris, et al. (författare) Unravelling 3D Dynamics and Hydrodynamics during Incorporation of Dielectric Particles to an Optical Trapping Site 2023 Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-0851 .- 1936-086X. ; 17:4, s. 3797-3808 Tidskriftsartikel (refereegranskat)abstract Mapping of the spatial and temporal motion of particles inside an optical field is critical for understanding and further improvement of the 3D spatio-temporal control over their optical trapping dynamics. However, it is not trivial to capture the 3D motion, and most imaging systems only capture a 2D projection of the 3D motion, in which the information about the axial movement is not directly available. In this work, we resolve the 3D incorporation trajectories of 200 nm fluorescent polystyrene particles in an optical trapping site under different optical experimental conditions using a recently developed widefield multiplane microscope (imaging volume of 50 × 50 × 4 μm3). The particles are gathered at the focus following some preferential 3D channels that show a shallow cone distribution. We demonstrate that the radial and the axial flow speed components depend on the axial distance from the focus, which is directly related to the scattering/gradient optical forces. While particle velocities and trajectories are mainly determined by the trapping laser profile, they cannot be completely explained without considering collective effects resulting from hydrodynamic forces.
2.	Mantzouki, Evanthia, et al. (författare) Temperature Effects Explain Continental Scale Distribution of Cyanobacterial Toxins 2018 Ingår i: Toxins. - : MDPI. - 2072-6651. ; 10:4 Tidskriftsartikel (refereegranskat)abstract Insight into how environmental change determines the production and distribution of cyanobacterial toxins is necessary for risk assessment. Management guidelines currently focus on hepatotoxins (microcystins). Increasing attention is given to other classes, such as neurotoxins (e.g., anatoxin-a) and cytotoxins (e.g., cylindrospermopsin) due to their potency. Most studies examine the relationship between individual toxin variants and environmental factors, such as nutrients, temperature and light. In summer 2015, we collected samples across Europe to investigate the effect of nutrient and temperature gradients on the variability of toxin production at a continental scale. Direct and indirect effects of temperature were the main drivers of the spatial distribution in the toxins produced by the cyanobacterial community, the toxin concentrations and toxin quota. Generalized linear models showed that a Toxin Diversity Index (TDI) increased with latitude, while it decreased with water stability. Increases in TDI were explained through a significant increase in toxin variants such as MC-YR, anatoxin and cylindrospermopsin, accompanied by a decreasing presence of MC-LR. While global warming continues, the direct and indirect effects of increased lake temperatures will drive changes in the distribution of cyanobacterial toxins in Europe, potentially promoting selection of a few highly toxic species or strains.
3.	Ademuyiwa, Adesoji O., et al. (författare) Determinants of morbidity and mortality following emergency abdominal surgery in children in low-income and middle-income countries 2016 Ingår i: BMJ Global Health. - : BMJ Publishing Group Ltd. - 2059-7908. ; 1:4 Tidskriftsartikel (refereegranskat)abstract Background: Child health is a key priority on the global health agenda, yet the provision of essential and emergency surgery in children is patchy in resource-poor regions. This study was aimed to determine the mortality risk for emergency abdominal paediatric surgery in low-income countries globally.Methods: Multicentre, international, prospective, cohort study. Self-selected surgical units performing emergency abdominal surgery submitted prespecified data for consecutive children aged <16 years during a 2-week period between July and December 2014. The United Nation's Human Development Index (HDI) was used to stratify countries. The main outcome measure was 30-day postoperative mortality, analysed by multilevel logistic regression.Results: This study included 1409 patients from 253 centres in 43 countries; 282 children were under 2 years of age. Among them, 265 (18.8%) were from low-HDI, 450 (31.9%) from middle-HDI and 694 (49.3%) from high-HDI countries. The most common operations performed were appendectomy, small bowel resection, pyloromyotomy and correction of intussusception. After adjustment for patient and hospital risk factors, child mortality at 30 days was significantly higher in low-HDI (adjusted OR 7.14 (95% CI 2.52 to 20.23), p<0.001) and middle-HDI (4.42 (1.44 to 13.56), p=0.009) countries compared with high-HDI countries, translating to 40 excess deaths per 1000 procedures performed.Conclusions: Adjusted mortality in children following emergency abdominal surgery may be as high as 7 times greater in low-HDI and middle-HDI countries compared with high-HDI countries. Effective provision of emergency essential surgery should be a key priority for global child health agendas.
4.	Banote, Rakesh Kumar, et al. (författare) Amyloid precursor protein-b facilitates cell adhesion during early development in zebrafish 2020 Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 10:1 Tidskriftsartikel (refereegranskat)abstract Understanding the biological function of amyloid beta (A beta) precursor protein (APP) beyond its role in Alzheimer's disease is emerging. Yet, its function during embryonic development is poorly understood. The zebrafish APP orthologue, Appb, is strongly expressed during early development but thus far has only been studied via morpholino-mediated knockdown. Zebrafish enables analysis of cellular processes in an ontogenic context, which is limited in many other vertebrates. We characterized zebrafish carrying a homozygous mutation that introduces a premature stop in exon 2 of the appb gene. We report that appb mutants are significantly smaller until 2 dpf and display perturbed enveloping layer (EVL) integrity and cell protrusions at the blastula stage. Moreover, appb mutants surviving beyond 48 hpf exhibited no behavioral defects at 6 dpf and developed into healthy and fertile adults. The expression of the app family member, appa, was also found to be altered in appb mutants. Taken together, we show that appb is involved in the initial development of zebrafish by supporting the integrity of the EVL, likely by mediating cell adhesion properties. The loss of Appb might then be compensated for by other app family members to maintain normal development.
5.	Beal, Jacob, et al. (författare) Robust estimation of bacterial cell count from optical density 2020 Ingår i: Communications Biology. - : Springer Science and Business Media LLC. - 2399-3642. ; 3:1 Tidskriftsartikel (refereegranskat)abstract Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data.
6.	Camacho Dejay, Rafael, et al. (författare) Fluorescence polarization measures energy funneling in single light-harvesting antennas-LH2 vs conjugated polymers. 2015 Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 5 Tidskriftsartikel (refereegranskat)abstract Numerous approaches have been proposed to mimic natural photosynthesis using artificial antenna systems, such as conjugated polymers (CPs), dendrimers, and J-aggregates. As a result, there is a need to characterize and compare the excitation energy transfer (EET) properties of various natural and artificial antennas. Here we experimentally show that EET in single antennas can be characterized by 2D polarization imaging using the single funnel approximation. This methodology addresses the ability of an individual antenna to transfer its absorbed energy towards a single pool of emissive states, using a single parameter called energy funneling efficiency (ε). We studied individual peripheral antennas of purple bacteria (LH2) and single CP chains of 20 nm length. As expected from a perfect antenna, LH2s showed funneling efficiencies close to unity. In contrast, CPs showed lower average funneling efficiencies, greatly varying from molecule to molecule. Cyclodextrin insulation of the conjugated backbone improves EET, increasing the fraction of CPs possessing ε = 1. Comparison between LH2s and CPs shows the importance of the protection systems and the protein scaffold of LH2, which keep the chromophores in functional form and at such geometrical arrangement that ensures excellent EET.
7.	Camacho Dejay, Rafael, et al. (författare) Inhomogeneous Quenching as a Limit of the Correlation Between Fluorescence Polarization and Conformation of Single Molecules 2013 Ingår i: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 4:6, s. 1053-1058 Tidskriftsartikel (refereegranskat)abstract The photophysical properties of conjugated polymers (CPs) largely depend on the interactions between the CP and its environment. We present a study of two polymers with identical conjugated backbones, bare and insulated, that showed different fluorescence excitation modulation depth histograms. However, the polarization differences are not related to differences in conformation, as commonly believed, but to the existence of "dark" chromophores in the bare polymer that are statically quenched. This results in inhomogeneous quenching of the polymer chain that breaks the correlation between excitation fluorescence polarization and conjugated polymer chain conformation.
8.	Camacho Dejay, Rafael, et al. (författare) Polarization Imaging of Emissive Charge Transfer States in Polymer/Fullerene Blends 2014 Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 26:23, s. 6695-6704 Tidskriftsartikel (refereegranskat)abstract Photoexcitation of conjugated polymerfullerene blends results in population of a local charge transfer (CT) state at the interface between the two materials. The competition between recombination and dissociation of this interfacial state limits the generation of fully separated free charges. Therefore, a detailed understanding of the CT states is critical for building a comprehensive picture of the organic solar cells operation. We applied a new fluorescence microscopy method called two-dimensional polarization imaging to gain insight into the orientation of the transition dipole moments of the CT states, and the associated excitation energy transfer processes in TQ1:PCBM blend films. The polymer phase was oriented mechanically to relate the polymer dipole moment orientation to that of the CT states. CT state formation was observed to be much faster than energy transfer in the polymer phase. However, after being formed an emissive CT state does not exchange excitation energy with other CT states, suggesting that they are spatially and/or energetically isolated. We found that the quantum yield of the CT emission is smaller for CT states spatially located in the highly oriented polymer domains, which is interpreted as the result of enhanced CT state dissociation in highly ordered structures.
9.	Camacho Dejay, Rafael (författare) Polarization portraits of lightharvesting antennas: from single molecule spectroscopy to imaging 2014 Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract Multichromophoric systems are very important in photosynthesis and any device that uses solar energy for its operation. This is because multichromophoric light-harvesting antennas are responsible for the absorption of light and the efficient transfer of the absorbed energy toward distinct places where it is to be used or stored. Over the last 10 years polarization sensitive single molecule methods have been extensively used to study the chromophore organisation and excitation energy transfer processes in lightharvesting antennas. In general, these methods probe in separate experiments the fluorescence excitation and emission polarization properties of the sample. This approach unfortunately averages out meaningful correlations between the polarization properties of the chromophores preferentially absorbing light, and the polarization state of the emitted fluorescence. Therefore, in 2009 an alternative method was proposed to detect these correlations called two dimensional polarization imaging. This is done by measuring a two dimensional function that describes the fluorescence intensity and polarization of a single object as a function of the electric field´s direction of the linearly polarized excitation light. However, in spite of the development of the technique, the main challenge still was to extract the excitation energy transfer information from the data. In this thesis we report the further understanding of the theoretical and experimental challenges developed for two dimension polarization imaging. Our development made possible the quantitative characterization of the excitation energy transfer efficiency of individual light-harvesting antennas, such as the LH2 complex and conjugated polymers, through a model based on a single funnel approximation. This method can be used to assess the “quality” of an artificial light harvesting antenna before trying it in a device. Further, we showed that our methodology is not only beneficial for studying of single molecules, but also can be used as a fluorescence imaging microscopy where parameters related to energy transfer and the chromophore organisation serve as imaging contrast. Two dimensional polarization imaging in combination with the single funnel approximation was successfully used to study thin films of a solar cell material, and is being tested on cell cultures and histological samples. The energy transfer sensitivity of our imaging technique opens exciting applications in life sciences for the study of biologically relevant systems, such as the aggregation of proteins involved in the causes of various diseases.
10.	Camacho Dejay, Rafael, et al. (författare) Quantitative characterization of light-harvesting efficiency in single molecules and nanoparticles by 2D polarization microscopy: Experimental and theoretical challenges 2012 Ingår i: Chemical Physics. - : Elsevier BV. - 0301-0104. ; 406, s. 30-40 Tidskriftsartikel (refereegranskat)abstract General problem of extracting intramolecular energy transfer information from fluorescence and fluorescence excitation polarization experiments at single molecule level is presented. A single funnel approximation is shown to be a very powerful approach to model the polarization data obtained by recently emerged 2-dimensional polarization single molecule imaging technique [O. Mirzov et al., Small 5 (2009) 1877]. Using this approximation a parameter characterising quantitatively light-harvesting efficiency of an individual light-harvesting antenna can be readily obtained. Technical details of 2D polarization imaging and practical methods of avoiding polarization artefact in fluorescence microscopy are discussed. (C) 2012 Elsevier B. V. All rights reserved.
11.	Camacho, Rafael, et al. (författare) 2D polarization imaging as a low-cost fluorescence method to detect α-synuclein aggregation ex vivo in models of Parkinson’s disease 2018 Ingår i: Communications Biology. - : Springer Science and Business Media LLC. - 2399-3642. ; 1 Tidskriftsartikel (refereegranskat)abstract A hallmark of Parkinson’s disease is the formation of large protein-rich aggregates in neurons, where α-synuclein is the most abundant protein. A standard approach to visualize aggregation is to fluorescently label the proteins of interest. Then, highly fluorescent regions are assumed to contain aggregated proteins. However, fluorescence brightness alone cannot discriminate micrometer-sized regions with high expression of non-aggregated proteins from regions where the proteins are aggregated on the molecular scale. Here, we demonstrate that 2-dimensional polarization imaging can discriminate between preformed non-aggregated and aggregated forms of α-synuclein, and detect increased aggregation in brain tissues of transgenic mice. This imaging method assesses homo-FRET between labels by measuring fluorescence polarization in excitation and emission simultaneously, which translates into higher contrast than fluorescence anisotropy imaging. Exploring earlier aggregation states of α-synuclein using such technically simple imaging method could lead to crucial improvements in our understanding of α-synuclein-mediated pathology in Parkinson’s Disease.
12.	Camacho, Rafael, et al. (författare) Fluorescence Anisotropy Reloaded—Emerging Polarization Microscopy Methods for Assessing Chromophores' Organization and Excitation Energy Transfer in Single Molecules, Particles, Films, and Beyond 2019 Ingår i: Advanced Materials. - : Wiley. - 0935-9648 .- 1521-4095. ; 31:22 Forskningsöversikt (refereegranskat)abstract Fluorescence polarization is widely used to assess the orientation/rotation of molecules, and the excitation energy transfer between closely located chromophores. Emerging since the 1990s, single molecule fluorescence spectroscopy and imaging stimulate the application of light polarization for studying molecular organization and energy transfer beyond ensemble averaging. Here, traditional fluorescence polarization and linear dichroism methods used for bulk samples are compared with techniques specially developed for, or inspired by, single molecule fluorescence spectroscopy. Techniques for assessing energy transfer in anisotropic samples, where the traditional fluorescence anisotropy framework is not readily applicable, are discussed in depth. It is shown that the concept of a polarization portrait and the single funnel approximation can lay the foundation for alternative energy transfer metrics. Examples ranging from fundamental studies of photoactive materials (conjugated polymers, light-harvesting aggregates, and perovskite semiconductors) to Förster resonant energy transfer (FRET)-based biomedical imaging are presented. Furthermore, novel uses of light polarization for super-resolution optical imaging are mentioned as well as strategies for avoiding artifacts in polarization microscopy.
13.	Donis, Daphne, et al. (författare) Stratification strength and light climate explain variation in chlorophyll a at the continental scale in a European multilake survey in a heatwave summer 2021 Ingår i: Limnology and Oceanography. - : John Wiley & Sons. - 0024-3590 .- 1939-5590. ; 66:12, s. 4314-4333 Tidskriftsartikel (refereegranskat)abstract To determine the drivers of phytoplankton biomass, we collected standardized morphometric, physical, and biological data in 230 lakes across the Mediterranean, Continental, and Boreal climatic zones of the European continent. Multilinear regression models tested on this snapshot of mostly eutrophic lakes (median total phosphorus [TP] = 0.06 and total nitrogen [TN] = 0.7 mg L-1), and its subsets (2 depth types and 3 climatic zones), show that light climate and stratification strength were the most significant explanatory variables for chlorophyll a (Chl a) variance. TN was a significant predictor for phytoplankton biomass for shallow and continental lakes, while TP never appeared as an explanatory variable, suggesting that under high TP, light, which partially controls stratification strength, becomes limiting for phytoplankton development. Mediterranean lakes were the warmest yet most weakly stratified and had significantly less Chl a than Boreal lakes, where the temperature anomaly from the long-term average, during a summer heatwave was the highest (+4 degrees C) and showed a significant, exponential relationship with stratification strength. This European survey represents a summer snapshot of phytoplankton biomass and its drivers, and lends support that light and stratification metrics, which are both affected by climate change, are better predictors for phytoplankton biomass in nutrient-rich lakes than nutrient concentrations and surface temperature.
14.	Gerhard, Marina, et al. (författare) Microscopic insight into non-radiative decay in perovskite semiconductors from temperature-dependent luminescence blinking 2019 Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 10:1 Tidskriftsartikel (refereegranskat)abstract Organo-metal halide perovskites are promising solution-processed semiconductors, however, they possess diverse and largely not understood non-radiative mechanisms. Here, we resolve contributions of individual non-radiative recombination centers (quenchers) in nanocrystals of methylammonium lead iodide by studying their photoluminescence blinking caused by random switching of quenchers between active and passive states. We propose a model to describe the observed reduction of blinking upon cooling and determine energetic barriers of 0.2 to 0.8 eV for enabling the switching process, which points to ion migration as the underlying mechanism. Moreover, due to the strong influence of individual quenchers, the crystals show very individually-shaped photoluminescence enhancement upon cooling, suggesting that the high variety of activation energies of the PL enhancement reported in literature is not related to intrinsic properties but rather to the defect chemistry. Stabilizing the fluctuating quenchers in their passive states thus appears to be a promising strategy for improving the material quality.
15.	Huang, C. H., et al. (författare) The primeval optical evolving matter by optical binding inside and outside the photon beam 2022 Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 13:1 Tidskriftsartikel (refereegranskat)abstract Optical binding enables light-induced assembly of many particles within a focus area. Here, the authors demonstrate that optical binding can occur outside the irradiated area by scattered light interacting with the particles outside the focus, generating arc-shape potential wells for particle trapping. Optical binding has recently gained considerable attention because it enables the light-induced assembly of many-body systems; however, this phenomenon has only been described between directly irradiated particles. Here, we demonstrate that optical binding can occur outside the focal spot of a single tightly focused laser beam. By trapping at an interface, we assemble up to three gold nanoparticles with a linear arrangement which fully-occupies the laser focus. The trapping laser is efficiently scattered by this linear alignment and interacts with particles outside the focus area, generating several discrete arc-shape potential wells with a half-wavelength periodicity. Those external nanoparticles inside the arcs show a correlated motion not only with the linear aligned particles, but also between themselves even both are not directly illuminated. We propose that the particles are optically bound outside the focal spot by the back-scattered light and multi-channel light scattering, forming a dynamic optical binding network.
16.	Lin, Hongzhen, et al. (författare) Collective Fluorescence Blinking in Linear J-Aggregates Assisted by Long-Distance Exciton Migration. 2010 Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 10:2, s. 620-626 Tidskriftsartikel (refereegranskat)abstract Fluorescence blinking corresponding to collective quenching of up to 100 dye monomers is reported for individual J-aggregates of a perylene bisimide (PBI) dye. This implies an exciton diffusion length up to 70 nm in these one-dimensional assemblies. The number of quenched monomers was directly measured by comparing the fluorescence brightness of the J-aggregates with that of noncoupled PBI molecules. This brightness analysis technique is useful for unraveling photophysical parameters of any individual fluorescent nanosystem.
17.	Louis, B., et al. (författare) Fast-tracking of single emitters in large volumes with nanometer precision 2020 Ingår i: Optics Express. - : Optica Publishing Group. - 1094-4087. ; 28:19, s. 28656-28671 Tidskriftsartikel (refereegranskat)abstract Multifocal plane microscopy allows for capturing images at different focal planes simultaneously. Using a proprietary prism which splits the emitted light into paths of different lengths, images at 8 different focal depths were obtained, covering a volume of 50x50x4 mu m(3). The position of single emitters was retrieved using a phasor-based approach across the different imaging planes, with better than 10 nm precision in the axial direction. We validated the accuracy of this approach by tracking fluorescent beads in 3D to calculate water viscosity. The fast acquisition rate (>100 fps) also enabled us to follow the capturing of 0.2 mu m fluorescent beads into an optical trap. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
18.	LOUIS, BORIS, et al. (författare) Fast-tracking of single emitters in large volumes with nanometer precision 2020 Ingår i: Optics Express. - 1094-4087. ; 28:19, s. 28656-28671 Tidskriftsartikel (refereegranskat)abstract Multifocal plane microscopy allows for capturing images at different focal planes simultaneously. Using a proprietary prism which splits the emitted light into paths of different lengths, images at 8 different focal depths were obtained, covering a volume of 50x50x4 μm3. The position of single emitters was retrieved using a phasor-based approach across the different imaging planes, with better than 10 nm precision in the axial direction. We validated the accuracy of this approach by tracking fluorescent beads in 3D to calculate water viscosity. The fast acquisition rate (>100 fps) also enabled us to follow the capturing of 0.2 μm fluorescent beads into an optical trap.
19.	Merdasa, Aboma, et al. (författare) Non-radiative processes in metal halide perovskite semiconductors probed by photoluminescence microscopy 2018 Ingår i: XIII International Conference on Hole Burning, Single Molecule, and Related Spectroscopies: Science and Applications (HBSM-2018). - : EDP Sciences. - 2101-6275. ; 190 Konferensbidrag (refereegranskat)abstract Organo metal halide perovskites are solution processed semiconductors that recently attracted a great attention. They possess a rather "soft" and (photo) chemically active solid structure allowing for ion migration and other mass diffusion processes. This is a likely reason why non-radiative recombination centres in these materials are activated and deactivated on relatively slow time-scales. This dynamics reveals as photoluminescence (PL) fluctuations (blinking) of individual microcrystals and local areas of films and allows for application of a broad range of single molecule spectroscopy methods including optical super-resolution. Studying PL blinking resolves properties of individual non-radiative centres and helps to unravel their chemical nature.
20.	Merdasa, Aboma, et al. (författare) Single Levy States-Disorder Induced Energy Funnels in Molecular Aggregates 2014 Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 14:12, s. 6774-6781 Tidskriftsartikel (refereegranskat)abstract Using fluorescence super-resolution microscopy we studied simultaneous spectral, spatial localization, and blinking behavior of individual 1D J-aggregates. Excitons migrating 100 nm are funneled to a trap appearing as an additional red-shifted blinking fluorescence band. We propose that the trap is a Frenkel exciton state formed much below the main exciton band edge due to an environmentally induced heavy-tailed Levy disorder. This points to disorder engineering as a new avenue in controlling light-harvesting in molecular ensembles.
21.	Merdasa, Aboma, et al. (författare) "Supertrap" at Work: Extremely Efficient Nonradiative Recombination Channels in MAPbI3 Perovskites Revealed by Luminescence Super-Resolution Imaging and Spectroscopy 2017 Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-0851 .- 1936-086X. ; 11:6, s. 5391-5404 Tidskriftsartikel (refereegranskat)abstract Organo-metal halide perovskites are some of the most promising materials for the new generation of low-cost photovoltaic and light-emitting devices. Their solution processability is a beneficial trait, although it leads to a spatial inhomogeneity of perovskite films with a variation of the trap state density at the nanoscale. Comprehending their properties using traditional spectroscopy therefore becomes difficult, calling for a combination with microscopy in order to see beyond the ensemble-averaged response. We studied photoluminescence (PL) blinking of micrometer-sized individual methylammonium lead iodide (MAPbI3) perovskite polycrystals, as well as monocrystalline microrods up to 10 μm long. We correlated their PL dynamics with structure employing scanning electron and optical super-resolution microscopy. Combining super-resolution localization imaging and super-resolution optical fluctuation imaging (SOFI), we could detect and quantify preferential emitting regions in polycrystals exhibiting different types of blinking. We propose that blinking in MAPbI3 occurs by the activation/passivation of a "supertrap" which presumably is a donor-acceptor pair able to trap both electrons and holes. As such, nonradiative recombination via supertraps, in spite being present at a rather low concentrations (1012-1015 cm-3), is much more efficient than via all other defect states present in the material at higher concentrations (1016-1018 cm-3). We speculate that activation/deactivation of a supertrap occurs by its temporary dissociation into free donor and acceptor impurities. We found that supertraps are most efficient in structurally homogeneous and large MAPbI3 crystals where carrier diffusion is efficient, which may therefore pose limitations on the efficiency of perovskite-based devices.
22.	Michno, Wojciech, 1992, et al. (författare) Chemical traits of cerebral amyloid angiopathy in familial British-, Danish-, and non-Alzheimer 's dementias 2022 Ingår i: Journal of Neurochemistry. - : Wiley. - 0022-3042 .- 1471-4159. ; 163:3, s. 233-246 Tidskriftsartikel (refereegranskat)abstract Familial British dementia (FBD) and familial Danish dementia (FDD) are autosomal dominant forms of dementia caused by mutations in the integral membrane protein 2B (ITM2B, also known as BRI2) gene. Secretase processing of mutant BRI2 leads to secretion and deposition of BRI2-derived amyloidogenic peptides, ABri and ADan that resemble APP/beta-amyloid (A beta) pathology, which is characteristic of Alzheimer's disease (AD). Amyloid pathology in FBD/FDD manifests itself predominantly in the microvasculature by ABri/ADan containing cerebral amyloid angiopathy (CAA). While ABri and ADan peptide sequences differ only in a few C-terminal amino acids, CAA in FDD is characterized by co-aggregation of ADan with A beta, while in contrast no A beta deposition is observed in FBD. The fact that FDD patients display an earlier and more severe disease onset than FBD suggests a potential role of ADan and A beta co-aggregation that promotes a more rapid disease progression in FDD compared to FBD. It is therefore critical to delineate the chemical signatures of amyloid aggregation in these two vascular dementias. This in turn will increase the knowledge on the pathophysiology of these diseases and the pathogenic role of heterogenous amyloid peptide interactions and deposition, respectively. Herein, we used matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) in combination with hyperspectral, confocal microscopy based on luminescent conjugated oligothiophene probes (LCO) to delineate the structural traits and associated amyloid peptide patterns of single CAA in postmortem brain tissue of patients with FBD, FDD as well as sporadic CAA without AD (CAA+) that show pronounced CAA without parenchymal plaques. The results show that CAA in both FBD and FDD consist of N-terminally truncated- and pyroglutamate-modified amyloid peptide species (ADan and ABri), but that ADan peptides in FDD are also extensively C-terminally truncated as compared to ABri in FBD, which contributes to hydrophobicity of ADan species. Further, CAA in FDD showed co-deposition with A beta x-42 and A beta x-40 species. CAA+ vessels were structurally more mature than FDD/FBD CAA and contained significant amounts of pyroglutamated A beta. When compared with FDD, A beta in CAA+ showed more C-terminal and less N-terminally truncations. In FDD, ADan showed spatial co-localization with A beta 3pE-40 and A beta 3-40 but not with A beta x-42 species. This suggests an increased aggregation propensity of A beta in FDD that promotes co-aggregation of both A beta and ADan. Further, CAA maturity appears to be mainly governed by A beta content based on the significantly higher 500/580 patterns observed in CAA+ than in FDD and FBD, respectively. Together this is the first study of its kind on comprehensive delineation of Bri2 and APP-derived amyloid peptides in single vascular plaques in both FDD/FBD and sporadic CAA that provides new insight in non-AD-related vascular amyloid pathology.
23.	Reveiz, Ludovic, et al. (författare) Stress ulcer, gastritis, and gastrointestinal bleeding prophylaxis in critically ill pediatric patients : a systematic review 2010 Ingår i: Pediatric Critical Care Medicine. - : Lippincott Williams & Wilkins. - 1529-7535 .- 1947-3893. ; 11:1, s. 124-132 Tidskriftsartikel (refereegranskat)abstract OBJECTIVE: To identify and evaluate the quality of evidence supporting prophylactic use of treatments for stress ulcers and upper gastrointestinal bleeding. Stress ulcers, erosions of the stomach and duodenum, and upper gastrointestinal bleeding are well-known complications of critical illness in children admitted to the pediatric intensive care unit.DATA SOURCES: Studies were identified from the Cochrane Central Register of Controlled Trials, PUBMED; LILACS; Scirus. We also scanned bibliographies of relevant studies.STUDY SELECTION: This systematic review of randomized controlled trials assessed the effects of drugs for stress-related ulcers, gastritis, and upper gastrointestinal bleeding in critically ill children admitted to the pediatric intensive care unit.DATA EXTRACTION AND SYNTHESIS: Two reviewers independently extracted the relevant data. Most randomized controlled trials were judged as having unclear risk of bias. When pooling two randomized controlled trials, treatment was significantly more effective in preventing upper gastrointestinal bleeding (macroscopic or important bleeding) compared with no treatment (two studies = 300 participants; relative risk, 0.41; 95% confidence interval, 0.19-0.91; I = 12%). Meta-analysis of two studies found no significant difference in death rates among groups (two randomized controlled trials = 132 participants; relative risk, 1.39; 95% confidence interval, 0.70-2.79; I = 4%). The rate of pneumonia was not significantly different when comparing treatment and no treatment in one study. When comparing ranitidine with no treatment, significant differences were found in the proportion of mechanically ventilated children with normal gastric mucosal endoscopic findings by histologic specimens (one randomized controlled trial = 48 participants; relative risk, 3.53; 95% confidence interval, 1.34-9.29). No significant differences were found when comparing different drugs (omeprazole, ranitidine, sucralfate, famotidine, amalgate), doses, or regimens for main outcomes (deaths, endoscopic findings of erosion or ulcers, upper gastrointestinal bleeding, or pneumonia).CONCLUSIONS: Although pooled data of two studies suggested that critically ill pediatric patients may benefit from receiving prophylactic treatment to prevent upper gastrointestinal bleeding, we found that high-quality evidence to guide clinical practice is still limited.
24.	Roselli, Sandra, et al. (författare) APP-BACE1 Interaction and Intracellular Localization Regulate A beta Production in iPSC-Derived Cortical Neurons 2023 Ingår i: Cellular and Molecular Neurobiology. - 0272-4340. ; 43, s. 3653-3668 Tidskriftsartikel (refereegranskat)abstract Alzheimer's disease (AD) is characterized pathologically by amyloid beta (A beta)-containing plaques. Generation of A beta from amyloid precursor protein (APP) by two enzymes, beta- and gamma-secretase, has therefore been in the AD research spotlight for decades. Despite this, how the physical interaction of APP with the secretases influences APP processing is not fully understood. Herein, we compared two genetically identical human iPSC-derived neuronal cell types: low A beta-secreting neuroprogenitor cells (NPCs) and high A beta-secreting mature neurons, as models of low versus high A beta production. We investigated levels of substrate, enzymes and products of APP amyloidogenic processing and correlated them with the proximity of APP to beta- and gamma-secretase in endo-lysosomal organelles. In mature neurons, increased colocalization of full-length APP with the beta-secretase BACE1 correlated with increased beta-cleavage product sAPP beta. Increased flAPP/BACE1 colocalization was mainly found in early endosomes. In the same way, increased colocalization of APP-derived C-terminal fragment (CTF) with presenilin-1 (PSEN1), the catalytic subunit of gamma-secretase, was seen in neurons as compared to NPCs. Furthermore, most of the interaction of APP with BACE1 in low A beta-secreting NPCs seemed to derive from CTF, the remaining APP part after BACE1 cleavage, indicating a possible novel product-enzyme inhibition. In conclusion, our results suggest that interaction of APP and APP cleavage products with their secretases can regulate A beta production both positively and negatively. beta- and gamma-Secretases are difficult targets for AD treatment due to their ubiquitous nature and wide range of substrates. Therefore, targeting APP-secretase interactions could be a novel treatment strategy for AD.
25.	Sartelli, Massimo, et al. (författare) Ten golden rules for optimal antibiotic use in hospital settings: the WARNING call to action 2023 Ingår i: WORLD JOURNAL OF EMERGENCY SURGERY. - 1749-7922. ; 18:1 Forskningsöversikt (refereegranskat)abstract Antibiotics are recognized widely for their benefits when used appropriately. However, they are often used inappropriately despite the importance of responsible use within good clinical practice. Effective antibiotic treatment is an essential component of universal healthcare, and it is a global responsibility to ensure appropriate use. Currently, pharmaceutical companies have little incentive to develop new antibiotics due to scientific, regulatory, and financial barriers, further emphasizing the importance of appropriate antibiotic use. To address this issue, the Global Alliance for Infections in Surgery established an international multidisciplinary task force of 295 experts from 115 countries with different backgrounds. The task force developed a position statement called WARNING (Worldwide Antimicrobial Resistance National/International Network Group) aimed at raising awareness of antimicrobial resistance and improving antibiotic prescribing practices worldwide. The statement outlined is 10 axioms, or "golden rules," for the appropriate use of antibiotics that all healthcare workers should consistently adhere in clinical practice.
26.	Shi, Juanzi, et al. (författare) Energy transfer in multi-funnel systems quantitatively assessed by two-dimensional polarization imaging and single funnel approximation: From single molecules to ensembles 2022 Ingår i: The Journal of chemical physics. - : AIP Publishing. - 1089-7690 .- 0021-9606. ; 156:7 Tidskriftsartikel (refereegranskat)abstract Two-dimensional polarization imaging (2D POLIM) is an experimental method where correlations between fluorescence excitation- and fluorescence emission-polarization properties are measured. One way to analyze 2D POLIM data is to apply a so-called single funnel approximation (SFA). The SFA allows for quantitative assessment of energy transfer between chromophores with identical spectra [homo-FRET (Förster resonance energy transfer)]. In this paper, we run a series of computer experiments to investigate the applicability of the analysis based on the SFA to various systems ranging from single multichromophoric systems to isotropic ensembles. By setting various scenarios of energy transfer between individual chromophores within a single object, we were able to define the borders of the practical application of SFA. It allowed us to reach a more comprehensive interpretation of the experimental data in terms of uncovering the internal arrangement of chromophores in the system and energy transfer between them. We also found that the SFA can always formally explain the data for isotropic ensembles and derived a formula connecting the energy funneling efficiency parameter and traditional fluorescence anisotropy.
27.	Siebert, Ronald, et al. (författare) Fluorescence quenching in Zn2+-bis-terpyridine coordination polymers: a single molecule study 2012 Ingår i: Journal of Materials Chemistry. - : Royal Society of Chemistry (RSC). - 1364-5501 .- 0959-9428. ; 22:31, s. 16041-16050 Tidskriftsartikel (refereegranskat)abstract A Zn2+-bis-terpyridine coordination polymer is investigated by single-molecule fluorescence spectroscopy (SMS). The bis-terpyridine ligands of the coordination polymers bear conjugated chromophores connecting the terpyridine spheres of the ligands, which resemble structural features of MEH-PPV. To the best of our knowledge this paper presents the first systematic SMS study on Zn2+-bis-terpyridine coordination polymers. Upon incorporation of free chromophores into the polymer, the fluorescence quantum yield of individual chromophores appears to be reduced. The reason for the reduced emission per chromophore in a polymer is investigated by brightness studies on single isolated polymer molecules. Furthermore, the experiments reveal that the Zn2+-bis-terpyridine coordination polymer contains a significantly larger fraction of effective chromophores, compared to one of the most common conjugated polymers, e. g., MEH-PPV. This finding is attributed to the particularly rigid geometry of the system at hand, which was corroborated by polarization-dependent experiments. Time-resolved experiments identified two different types of intensity fluctuations: small amplitude intensity fluctuations might correlate with switching of individual chromophores by structural fluctuations, while large amplitude jumps switch off the emission of the entire molecule. Finally, experiments under different atmospheric conditions offer further insights into the molecular mechanism and the nature of the quenchers involved in the blinking.
28.	Thomsson, Daniel, et al. (författare) Cyclodextrin Insulation Prevents Static Quenching of Conjugated Polymer Fluorescence at the Single Molecule Level. 2013 Ingår i: Small. - : Wiley. - 1613-6829 .- 1613-6810. ; 9:15, s. 2619-2627 Tidskriftsartikel (refereegranskat)abstract Conjugated polymers (CPs) are promising materials for fluorescence imaging application. However, a significant problem in this field is the unexplained abnormally low fluorescence brightness (or number of fluorescence photons detected per one excitation photon) exhibited by most of CP single chains in solid polymer hosts. Here it is shown that this detrimental effect can be fully avoided for short chains of polyfluorene-bis-vinylphenylene (PFBV) embedded in a host polymer matrix of PMMA, if the conjugated backbone is insulated by cyclodextrin rings to form a polyrotaxane (PFBV-Rtx). Fluorescence kinetics and quantum yields are measured for the polymers in liquid solutions, pristine films, and solid PMMA blends. The fluorescence brightness of PFBV-Rtx single chains dispersed in a solid PMMA is very close to that expected for a chain with 100% fluorescence quantum yield, while the unprotected PFBV chains of the same length possess 4 times lower brightness. Despite this, the fluorescence decay kinetics are the same for both polymers, suggesting the presence of static or ultrafast fluorescence quenching in the unprotected polymer. About 80% of an unprotected PFBV chain is estimated to be completely quenched. The hypothesis is that the cyclodextrin rings prevent the quenching by working as 'bumpers' reducing the mechanical forces applied by the host polymer to the conjugated backbone and help retaining its conformational freedom. While providing a recipe for making CP fluorescence bright at the single-molecule level, these results identify a lack of fundamental understanding in the community of the influence of the environment on excited states in conjugated materials.
29.	Tian, Yuxi, et al. (författare) Organization of Bacteriochlorophylls in Individual Chlorosomes from Chlorobaculum tepidum Studied by 2-Dimensional Polarization Fluorescence Microscopy 2011 Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 133:43, s. 17192-17199 Tidskriftsartikel (refereegranskat)abstract Chlorosomes are the largest and most efficient natural light-harvesting systems and contain supramolecular assemblies of bacteriochlorophylls that are organized without proteins. Despite a recent structure determination for chlorosomes from Chlorobaculum tepidum (Ganapathy et al. Proc. Natl. Acad. Sci. U.S.A. 2009, 106, 8525), the issue of a possible large structural disorder is still discussed controversially. We have studied individual chlorosomes prepared under very carefully controlled growth condition by a novel 2-dimensional polarization single molecule imaging technique giving polarization information for both fluorescence excitation and emission simultaneously. Contrary to the existing literature data, the polarization degree or modulation depth (M) for both excitation (absorption) and emission (fluorescence) showed extremely narrow distributions. The fluorescence was always highly polarized with M approximate to 0.77, independent of the excitation wavelength. Moreover, the fluorescence spectra of individual chlorosomes were identical within the error limits. These results lead us to conclude that all chlorosomes possess the same type of internal organization in terms of the arrangement of the bacteriochlorophyll c transition dipole moments and their total excitonic transition dipole possess a cylindrical symmetry in agreement with the previously suggested concentric multitubular chlorophyll aggregate organization (Ganapathy et al. Proc. Natl. Acad. Sci. U.S.A. 2009, 106, 8525).
30.	Tubasum, Sumera, et al. (författare) Evidence of excited state localization and static disorder in LH2 investigated by 2D-polarization single-molecule imaging at room temperature. 2013 Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 15:45, s. 19862-19869 Tidskriftsartikel (refereegranskat)abstract Two-dimensional polarization fluorescence imaging of single light harvesting complexes 2 (LH2) of Rps. acidophila was carried out to investigate the polarization properties of excitation and fluorescence emission simultaneously, at room temperature. In two separate experiments we excited LH2 with a spectrally narrow laser line matched to the absorption bands of the two chromophore rings, B800 and B850, thereby indirectly and directly triggering fluorescence of the B850 exciton state. A correlation analysis of the polarization modulation depths in excitation and emission for a large number of single complexes was performed. Our results show, in comparison to B800, that the B850 ring is a more isotropic absorber due to the excitonic nature of its excited states. At the same time, we observed a strong tendency for LH2 to emit with dipolar character, from which preferential localization of the emissive exciton, stable for minutes, is inferred. We argue that the observed effects can consistently be explained by static energetic disorder and/or deformation of the complex, with possible involvement of exciton self-trapping.
31.	Tubasum, Sumera, et al. (författare) Protein Configuration Landscape Fluctuations Revealed by Exciton Transition Polarizations in Single Light Harvesting Complexes. 2016 Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 120:4, s. 724-732 Tidskriftsartikel (refereegranskat)abstract Protein is a flexible material with broad distribution of conformations forming an energy landscape of quasi-stationary states. Disentangling the system dynamics along this landscape is the key for understanding the functioning of the protein. Here we studied a photosynthetic antenna pigment-protein complex LH2 with single molecule two-dimensional polarization imaging. Modeling based on the Redfield relaxation theory well describes the observed polarization properties of LH2 fluorescence and fluorescence excitation, strongly suggesting that at 77 K the conformational subspace of the LH2 is limited to about three configurations with relatively frequent switching among each other. At room temperature the next level of fluctuations determines the conformational dynamics. The results support the multitier model of the energy landscape of proteins and demonstrate the potential of the method for the studies of structural dynamics in proteins.
32.	Täuber, Daniela, et al. (författare) Exploring the Electronic Band Structure of Organometal Halide Perovskite via Photoluminescence Anisotropy of Individual Nanocrystals 2016 Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 16:8, s. 5087-5094 Tidskriftsartikel (refereegranskat)abstract Understanding electronic processes in organometal halide perovskites, flourishing photovoltaic, and emitting materials requires unraveling the origin of their electronic transitions. Light polarization studies can provide important information regarding transition dipole moment orientations. Investigating individual methylammonium lead triiodide perovskite nanocrystals enabled us to detect the polarization of photoluminescence intensity and photoluminescence excitation, hidden in bulk samples by ensemble averaging. Polarization properties of the crystals were correlated with their photoluminescence spectra and electron microscopy images. We propose that distortion of PbI6 octahedra leads to peculiarities of the electronic band structure close to the band-edge. Namely, the lowest band transition possesses a transition dipole moment along the apical Pb-I-Pb bond resulting in polarized photoluminescence. Excitation of photoluminescence above the bandgap is unpolarized because it involves molecular orbitals delocalized both in the apical and equatorial directions of the perovskite octahedron. Trap-assisted emission at 77 K, rather surprisingly, was polarized similar to the bandgap emission.
33.	Vandaele, Johannes, et al. (författare) Structural characterization of fibrous synthetic hydrogels using fluorescence microscopy 2020 Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-683X .- 1744-6848. ; 16:17, s. 4210-4219 Tidskriftsartikel (refereegranskat)abstract The structural features of the matrix surrounding the cells play a crucial role in regulating their behavior. Here, we used fluorescence microscopy and customized analysis algorithms to characterize the architecture of fibrous hydrogel networks. As a model system, we investigated a new class of synthetic biomimetic material, hydrogels prepared from polyisocyanides. Our results show that these synthetic gels present a highly heterogeneous fibrous network, with pores reaching a few micrometers in diameter. By encapsulating HeLa cells in different hydrogels, we show that a more porous structure is linked to a higher proliferation rate. The approach described here, for the characterization of the network of fibrous hydrogels, can be easily applied to other polymer-based materials and provide new insights into the influence of structural features in cell behavior. This knowledge is crucial to develop the next generation of biomimetic materials for 3D cell models and tissue engineering applications.

Skapa referenser, mejla, bekava och länka

Länka till träfflistan

Träfflista för sökning "WFRF:(Camacho Rafael) "

Avgränsa träffmängd

År