1,720,967 research outputs found
Fluorescence correlation spectroscopy in sub-micrometric compartments and close to a wall
No full textAccounting for misalignments and thermal fluctuations in fluorescence correlation spectroscopy experiments on membranes
No full textSeveral authors have exploited the ability of the fluorescence correlation spectroscopy to probe motion at the molecular level. In a couple of decades, all their efforts have allowed the application of this technique even to the diffusion measurement of cellular components. Nowadays, the fluorescence correlation spectroscopy is considered a standard tool to measure diffusion in cells both in vivo and in vitro. Unfortunately, while the interpretation and the set-up have been consolidated for 3D diffusion measurements (i.e. diffusion in an aqueous solution), the experiments carried out on flat elements, such as membranes, show unusually high relative errors. Furthermore, long tail correlations are generally detected and ascribed to diffusion anomalies. The 2D fluorescence correlation measurements have been interpreted under certain hypotheses, whereby the membrane is assumed to be perfectly flat, motionless and aligned with the optical axes. Here, we investigated the robustness of these hypotheses, trying to understand, in an elementary but not trivial way, how misalignments and thermal fluctuations affect the temporal correlation of the intensity fluctuation collected during measurements on membrane
Molecular Interactions in and Transport Properties of Densely Cross-linked Networks: A Time-resolved FTIR Spectroscopy Investigation
No full textTransport of water in an epoxy network with high cross-link d. was investigated at several water vapor activities by time-resolved FT-IR spectroscopy and gravimetric measurements. The anal. of the IR spectra provided information about the mol. interactions occurring in the system. In particular, several interaction complexes were identified and their structures were proposed. An est. was made of the concn. of the various water species present in the system, based on the knowledge of the resp. molar absorptivities. An excellent agreement between the spectroscopic and gravimetric detns. of sorbed water was found throughout. The evolution of the different water species was monitored by resolving the complex profile of the water spectrum in the nOH frequency range. This information, coupled with the results of the gravimetric anal., was used to evaluate the effect of polymer/penetrant H-bonding interactions on the diffusion process of water mols. Transport of the different water species was found to follow a Fickian behavior characterized by an effective diffusion coeff. which increases with total water concn
Gas sorption and transport in syndiotactic polystyrene with nanoporous crystalline phase.
No full textIn this contribution we analyze sorption and transport of several gases in semicryst. syndiotactic polystyrene with nanoporous cryst. d form. Investigation was performed on amorphous samples and on samples characterized by different degrees of crystallinity. Sorption isotherms of carbon dioxide, nitrogen and oxygen in the cryst. phase have been detd. starting from exptl. results obtained for semicryst. and amorphous samples. Corresponding isosteric heats of sorption were evaluated for the cryst. and amorphous phase. Permeation tests were also performed to gather information on mass transport properties of semicryst. samples, evaluating av. diffusivities of carbon dioxide and oxygen, in the limit of small concns. as function of degree of crystallinity
Fluorescence Correlation Spectroscopy of Nanomaterials
No full textThe first in-depth treatment of the synthesis, processing, and characterization of nanomaterials using lasers, ranging from fundamentals to the latest research results, this handy reference is divided into two main sections. After introducing the concepts of lasers, nanomaterials, nanoarchitectures and laser-material interactions in the first three chapters, the book goes on to discuss the synthesis of various nanomaterials in vacuum, gas and liquids. The second half discusses various nanomaterial characterization techniques involving lasers, from Raman and photoluminescence spectroscopies to light dynamic scattering, laser spectroscopy and such unusual techniques as laser photo acoustic, fluorescence correlation spectroscopy, ultrafast dynamics and laser-induced thermal pulses. The specialist authors adopt a practical approach throughout, with an emphasis on experiments, set-up, and results. Each chapter begins with an introduction and is uniform in covering the basic approaches, experimental setups, and dependencies of the particular method on different parameters, providing sufficient theory and modeling to understand the principles behind the technique
Fluorescence correlation spectroscopy in semiadhesive wall proximity
No full textWith examination of diffusion in heterogeneous media through fluorescence correlation spectroscopy, the temporal correlation of the intensity signal shows a long correlation tail and the characteristic diffusion time results are no longer easy to determine. Excluded volume and sticking effects have been proposed to justify such deviations from the standard behavior since all contribute and lead to anomalous diffusion mechanisms. Usually, the anomalous coefficient embodies all the effects of environmental heterogeneity providing too general explanations for the exotic diffusion recorded. Here, we investigated whether the reason of anomalies could be related to a lack of an adequate interpretative model for heterogeneous systems and how the presence of obstacles on the detection volume length scale could affect fluorescence correlation spectroscopy experiments. We report an original modeling of the autocorrelation function where fluorophores experience reflection or adsorption at a wall placed at distances comparable with the detection volume size. We successfully discriminate between steric and adhesion effects through the analysis of long time correlations and evaluate the adhesion strength through the evaluation of probability of being adsorbed and persistence time at the wall on reference data. The proposed model can be readily adopted to gain a better understanding of intracellular and nanoconfined diffusion opening the way for a more rational analysis of the diffusion mechanism in heterogeneous systems and further developing biological and biomedical application
Non-equilibrium compressible lattice theories accounting for hydrogen bonding interactions: Modelling water sorption thermodynamics in fluorinated polyimides
No full textIn this contribution the sorption thermodynamics of water in glassy fluorinated polyimides has been interpreted by using two non-equilibrium lattice models, accounting for hydrogen bond formation, which have been developed by extending, respectively, the Panayiotou–Sanchez (PS) and the Non-Random
Hydrogen Bonding (NRHB) equilibrium models to the case of glassy polymers. The procedure used to extend the equilibrium models follows the same line of thought utilized by Doghieri and Sarti in deriving the Non-Equilibrium Thermodynamics for Glassy Polymers (NET-GP) model.
The approach has been found to be successful in interpreting experimental water sorption isotherms in two different perfluorinated polyimides, namely 6FDA-ODA and 6FDA-6FpDA. The models have been also found to be capable of supplying a good qualitative and quantitative estimate of the number of
water–water and water/polymer hydrogen bonds, as emerged from the comparison of theoretical predictions with experimental data obtained by means of previous IR spectroscopic measurements
Exploring doxorubicin localization in eluting TiO2 nanotube arrays through fluorescence correlation spectroscopy analysis
No full textDrug elution properties of TiO2 nanotube arrays have been largely investigated by means of solely macroscopic observations. Controversial elution performances have been reported so far and a clear comprehension of these phenomena is still missing as a consequence of a lack of molecular investigation methods. Here we propose a way to discern drug elution properties of nanotubes through the evaluation of drug localization by Fluorescence Correlation Spectroscopy (FCS) analysis. We verified this method upon doxorubicin elution from differently loaded TiO2 nanotubes. Diverse elution profiles were obtained from nanotubes filled by soaking and wet vacuum impregnation methods. Impregnated nanotubes controlled drug diffusion up to thirty days, while soaked samples completed elution in seven days. FCS analysis of doxorubicin motion in loaded nanotubes clarified that more than 90% of drugs dwell preferentially in inter-nanotube spaces in soaked samples due to decorrelation in a 2D fashion, while a 97% fraction of molecules showed 1D mobility ascribable to displacements along the nanotube vertical axis of wet vacuum impregnated nanotubes. The diverse drug localizations inferred from FCS measurements, together with distinct drug-surface interaction strengths resulting from diverse drug filling techniques, could explain the variability in elution kinetics
- …
