1,720,978 research outputs found
Effect of metal nanoparticles on the photophysical behaviour of dye–silica conjugates
No full textFluorescein has been covalently entrapped into 120 nm silica beads in order to measure the effect of plasmonic gold nanoparticles, having 25 nm diameter, on the radiative processes of the dye. Two distinct regimes of enhancement and quenching of fluorescein emission have been observed, depending on the concentration of the metal adsorbed on the silica surface and the overlap between the SPR and the fluorescein spectra. At particle concentrations below 5.0 x 10(13) nanoparticles mL(-1), the fluorescence of the dye is enhanced, and this effect is more pronounced when the excitation wavelength matches the maximum of the extinction spectrum of the gold nanoparticles. When the concentration of gold is further increased, quenching occurs and it has been attributed to the SPR shift following the aggregation of the gold colloids on the silica surface. The invariance of the fluorescence lifetimes during the whole process indicates that the mechanism of fluorophore-nanoparticle interaction is mainly based on changes in the absorption efficiency of the organic dye
Delivery of lipophilic compounds through formation and controlled re-dissolution of organic nanoassemblies.
No full textOptimizing the preparation of hybrid nanoparticles to decouple fluorescence and photothermal effect.
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AFM Measurements to Investigate Particulates and Their Interactions with Biological Macromolecules
No full textDriving the Interactions between Organic Nanoparticles and Phospolipidic Membranes by an Easy Treatment of the Surface Stabilizer
No full textPolymer-stabilized perylene nanoparticles were prepd. through
a solvent exchange method. The formation of the
nanostructures in aq. soln. was confirmed by the appearance of
a red-shifted emission attributable to the formation of excimerlike
aggregates. The behavior of org. nanostructures in the
presence of lipid vesicles was investigated through steadystate
and time-resolved fluorescence measurements. When no
further surface treatment is applied to the nanoparticles,
changes in the decay times and emission spectra demonstrate
that inside the lipid bilayers the nanoparticles redissolve into
the monomeric form with a rate and efficiency detd. by the
working temp. (above and below the transition temp. Tm of the
phospholipid). On the other hand, when the stabilized shell is
UV-cured to induce photo-crosslinking of the polymeric chains,
the nanoparticle stability increases and their redissoln. in the
membrane is prevented. Confocal fluorescence images
support the data obtained in bulk. The results indicate that the
prepd. nanostructures could be successfully used either as
nanometric carriers for the delivery of poor water-sol. lipophilic
compds. or as imaging tools depending on the
rigidity/crosslinking degree of their polymeric stabilizer shell
Hierarchical Assembly of Nanostructures to Decouple Fluorescence and Photothermal Effect
No full textHybrid nanoparticles are designed and produced by a two-step procedure with the aim to obtain optically controlled multifunctional nanomaterials. In particular, using a sol gel method in alcoholic/water media, silica particles doped with 9-aminoacridine molecules are prepared with a mean diameter of 31 nm, which preserves the fluorescent properties of the dye. In a second step, these nanoparticles are capped with a thin (7 nm-size) gold shell whose growth does not quench the emission of the dye as proven by steady-state and time-resolved fluorescence measurements. The careful choice of the organic dye and the control of the metal layer growth make possible to completely uncouple the fluorescence and the plasmon bands of gold. The selective photoexcitation of fluorescence or plasmon absorption, leading to heat release, has been tested on phospholipidic membranes loaded with the prepared hybrid particles. Under 400-nm irradiation fluorescence is activated, which is used to image the membranes; upon 650-nm irradiation only the gold layer absorbs and efficiently converts light into heat leading to a temperature increase of about 10 degrees C in the surrounding medium which is responsible for the alteration of the membrane architecture
Evaluation of cytotoxicity effects of nanoparticles present in working environments: preliminary results.
No full textSilica nanoparticles assisted photodegradation of acridine orange in aqueous suspensions
No full texttSilica nanostructured materials are often used as catalyst support but their catalytic role has not beendeeply investigated yet. In the present study, the photocatalytic degradation of acridine orange zincchloride double salt (AO) has been studied using silica nanoparticles (NPs) as catalysts. NPs of differentsize (55 and 146 nm) were prepared by a sol–gel procedure and their surface was modified with aminogroups to investigate the role of the chemical groups linked to the silica surface on the dye degradation.The silica nanomaterials were fully characterized by use of transmission electron microscopy (TEM), zetapotential measurements and UV–vis spectrophotometric methods.The photodegradation experiments were carried out irradiating at 313 or 490 nm for 50 min the aque-ous samples containing the dye and the silica NPs of 55 or 146 nm in diameter. The photocatalyticdegradation of the dye was determined from the decrease of its fluorescence intensity. AO fluorescenceintensity did not change when bare SiO2beads were used as catalysts, whereas an efficient decoloration(up to 58%) was achieved with amino functionalized NPs, with a photodegradation rate constant valueof 0.136 m−1. The data collected from the degradation experiments demonstrated that the functionalgroups on the silica surface have a fundamental role in the efficiency of the degradation processe
Modelling the Optical Properties of Metal Nanoparticles: Analytical vs Finite Elements Simulation
No full textMetal nanoparticles are an important research field for their broad and various application. The modeling of their chemical and
physical properties is essential for the correct design of innovative materials. In this study the analytical simulation, based on the
bare Mie theory, is directly compared with the measured absorbance spectra of gold colloids, prepared through a seed-mediated
process. The goodness in the prediction of the particles dimension gives an indication on the level of precision of the model to
simulate the optical behavior of the sample. Then, a discrete simulation is performed, which implements finite element analysis; a
good level of agreement with the analytical model is obtained for single isolated nanoparticles, and additional properties like
electromagnetic behavior of the particles is modeled. At last the discrete simulation is used to explore complex particle
structures, whose analytical simulation is not possible, like dimer, nanoparticles chain and planar distribution. For these
configurations, the electric field is analyzed, with particular attention to the best configuration for the field enhancement, and the
trend of the absorption spectrum is studied as a function of the relative distance among the particles. The results indicate that the
plasmon resonance shifts to the red when array of particles are considered since 10 and 30 nm shift has been observed for a chain
of closely spaced nanoparticles and for a planar ordered nanoparticles, respectively
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