1,721,013 research outputs found
Investigations of multiphoton absorption in molecular systems in solution and in sol-gel matrices for nonlinear optical applications
No full textIn this work a study on multiphoton absorption processes of organic and inorganic molecules is presented. The nonlinear optical properties are investigated for the systems both in solution and embedded in sol-gel matrices. This study is aimed at their practical use in different nonlinear optical applications
Two-Photon Fluorescence Correlation Spectroscopy of Gold Nanoparticles under Stationary and Flow Conditions
No full textIn this work we report two-photon fluorescence correlation spectroscopy
experiments run on gold nanoparticles in aqueous solution. We compare the photophysical properties of nanoparticles obtained by the Turkevich method and by laser ablation as a function of increasing laser power. Fluorescence correlation spectroscopy curves for all nanoparticles show the rotational diffusion contribution at short lag times, even if the residual rotation contrast coefficient at high excitation laser power is lower for laser ablation nanoparticles with respect to Turkevich syntheses.
Moreover, in contrast to Turkevich nanoparticles, laser ablation ones do not show an increase of the number of bright tracers in the excitation volume under higher excitation power. Nanoparticles from Turkevich synthesis are also tested as possible flow tracers inside a very simple microfluidic device featuring a single straight channel.
Our findings confirm that gold nanoparticles can indeed be used as extremely sensitive probes to observe local flow inside micrometric size channels, for example, such as mammalian capillaries, since it can distinguish subtle changes in flow speed, as the ones imparted by a syringe pump
An optofluidic light detector based on the photoacoustic effect
No full textAn optofluidic light detector based on the photoacoustic effect is presented. The device performances are tested at 532 nm using a pulsed solid-state laser as light source and a potassium permanganate (KMnO4) water solution as active medium. As expected, the device shows linear response with respect to applied light irradiance. By changing flow rate the device sensitivity increases non-linearly. This change in sensitivity is mainly attributed to a rise in water temperature as the flow rate increases, leading to a higher thermal expansion coefficient. Changes of water temperature with applied flow rate are confirmed through independent fluorescence intensity experiments with Rhodamine B in water. Comparison of the photoacoustic and fluorescence data points out that the change in temperature inside the microfluidic device is not promoted by the absorbed laser light, but instead is mainly due to viscous friction
New sol-gel materials for high energy applications in nonlinear optics
No full textOrganic-inorganic hybrid materials, composed of inorganic oxide structures and interpenetrated cross-linked organic polymers, are promising candidates for electro/optical applications, combining the most important glasslike and
polymerlike properties. This is particularly true when large laser power density is used: these materials show high laser
damage resistance compared with that of polymeric systems.
A deep study of effects and causes of laser damage has never been done, especially for hybrid materials. The
mechanisms of optical damage depend on different factors like laser experimental parameters, such as pulse duration,
beam size and wavelength, or the microstructural characteristics and defects of the material.
Hybrid materials possessing desired shapes and optical and mechanical properties are well synthesized by the sol-gel
technique. The use of Glycidoxypropyltrimethoxysilane (GPTMS) allows preparing heterogeneous and resistant
materials, with good optical properties.
Different sol-gel matrices have been prepared in order to study their laser damage resistance. The possibility of varying
the catalysts and precursors or the synthesis protocol allows obtaining materials with similar chemical composition and
different microscopical properties. By this way, it is possible to study the laser damage threshold of these samples and to
find the way to enhance and optimize the laser damage resistance, useful in non-linear optical devices
Laser damage of glycidoxypropyltrimethoxysilane based hybrid materials
No full textThe preparation of solid samples, having specific optical properties, is one of the main goals for the realization of devices in the photonic
field. To this end, it is important to attain the best control of the optical properties in the final materials. The sol–gel technique is a
powerful synthesis method allowing the preparation of matrices with high stability, mechanical resistance and high optical quality. The
use of hybrid organic–inorganic precursors permits samples with different thicknesses, ranging from films of hundreds of nanometers to
bulk samples of millimeters, to be obtained. The control of the synthesis protocol and the choice of precursors and catalyst allows the
control of the final matrix microstructure, which is related to optical properties, like the laser damage threshold. In this work four different
matrices, based on glycidoxypropyltrimethoxysilane and Zr alcoxide, have been prepared through sol–gel synthesis. An interpenetrating
organic and inorganic network, controlled by the synthesis protocol, characterizes these matrices. The obtained materials show
high resistance to the optical damage and long term stability
BSA adsorption on gold nanoparticles investigated under static and flow conditions
No full textIn this work time- and frequency-resolved spectroscopic techniques are employed for the investigation of protein adsorption (protein corona formation) on gold nanoparticles. We will follow the interaction of ~ 20 nm citrate-capped gold nanoparticles with the model protein bovine serum albumin under both static and flow conditions, to monitor in details the binding process in the early stages. In parallel to standard techniques (UV-Visible absorption, circular dichroism and fluorescence spectroscopy), an advanced technique such as fluorescence correlation spectroscopy is employed for the characterization of the kinetic and thermodynamic constants involved in protein corona formation. The dissociation constant characterizing adsorption of bovine serum albumin on gold nanoparticles is measured in solutions under static conditions as a function of protein concentration. A preliminary characterization of the adsorption dynamic, instead, is achieved by fabrication of a simple Y shaped microfluidic device in polydimethylsiloxane and glass. Water solutions of nanoparticles and protein are injected in the two inlets and mixing of the two species occurs only in the central part of the main channel. Following the evolution of the fluorescence correlation spectroscopy signal along the main channel of the microfluidic device provides adsorption kinetic data with a time resolution defined only by the flow rate applied at the inlets
Time correlated fluorescence characterization of an asymmetrically focused flow in a microfluidic device
No full textIn this study, we explore and model the behavior of a prototype microfluidic device which employs two non-mixing fluids (sheath and inlet fluids) displaying an asymmetric focused flow, in the presence of a fluorescent dye. Fluorescence correlation spectroscopy is employed, allowing the precise measure of flow speeds across the channels and of the concentration profile of the central focused flux along the flow direction. The system is modeled via a standard Navier-Stokes finite-element approach, coupled to convection-diffusion equations for the solute. Simulations reproduce accurately the shape, the position, and the width of the velocity and concentration profiles along the central channel and across the transversal and vertical sections of the microfluidic device. The observed asymmetric flow with respect to the center of the channel is reproduced numerically with an error in the position determination smaller than 1%
FLIM-FRET analysis using Ca<sup>2+</sup> sensors in HeLa cells
No full textIn this work, FLIM-FRET experiments are performed in HeLa cells expressing a genetically encoded Ca2+ indicator (GECIs) based on FRET, called Cameleon probes. These sensors allow the analysis of Ca2+ dynamics in different cell compartments, such as mitochondria and cytosol. Cameleons are composed by two fluorescent proteins (FPs, donor and acceptor moieties) and two Ca2+ responsive elements that alter the FRET efficiency between the FPs, as a function of intracellular Ca2+ concentration. In particular, we focus on new generated Cameleon sensors where the Cyan Fluorescent Protein donor moiety has been replaced by mCerulean3. Since it is characterized by single fluorescence lifetime decay and higher brightness, mCerulean3 based sensors has permitted the application of FLIM approach for the determination of FRET efficiency. FLIM measurements, compared to intensity-based FRET analysis, have the advantages of being independent of fluorophore concentration, excitation intensity fluctuation, sample thickness, or photobleaching
Spatially controlled clustering of nucleotide-stabilized vesicles
Full text linkA two-step hierarchical self-assembly process is presented relying on the GMP-induced formation of vesicles, which then cluster into large aggregates upon the addition of Ag+-ions.</p
Highly Efficient Amplified Stimulated Emission from CdSe-CdS-ZnS Quantum Dot Doped Waveguides with Two-Photon Infrared Optical Pumping
No full textIn principle, a population inversion in semiconductor quantum
dots can be achieved through electrical, chemical or optical
pumping. To date however, it has only been successfully
demonstrated with optical pumping in the 1-photon absorption
range (i.e., above the semiconductor bandgap). Under
these conditions amplified stimulated emission (ASE) in 1-D
waveguides and lasing within microsphere cavities and distributed
feedback structures has been observed. In these studies,
it was demonstrated that for the archetypal CdSe system,
a given nanocrystal must encompass more than one electronhole
(e–h) pair for a population inversion to be achieved. This
value reflects the twofold degeneracy of the lowest electronic
state in the wurtzite crystal structure
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