Spectral and photophysical modifications of porphyrins attached to core-shell nanoparticles. Theory and experiment.

Plasmonic nanostructures, of which gold nanoparticles are the most elementary example, owe their unique properties to localized surface plasmons (LSP), the modes of free electron oscillation. LSP alter significantly electromagnetic field in the nanostructure neighborhood (i.e., near-field), which can modify the electric dipole transition rates in organic emitters. This study aims at investigating the influence of Au@SiO2core-shell nanoparticles on the photophysics of porphyrins covalently attached to the nanoparticles surface. Guided by theoretical predictions, three sets of gold nanoparticles of different sizes were coated with a silica layer of similar thickness. The outer silica surface was functionalized with either free-basemeso-tetraphenylporphyrin or its zinc complex. Absorption and emission bands of porphyrin overlap in energy with a gold nanoparticle LSP resonance that provides the field enhancement. Silica separates the emitters from the gold surface, while the gold core size tunes the energy of the LSP resonance. The signatures of weak-coupling regime have been observed. Apart from modified emission profiles and shortened S1lifetimes, Q band part intensity of the excitation spectra significantly increased with respect to the Soret band. The results were explained using classical transfer matrix simulations and electronic states kinetics, taking into account the photophysical properties of each chromophore. The calculations could reasonably well predict and explain the experimental outcomes. The discrepancies between the two were discussed.

Quantitative determination of the size dependence of surface plasmon resonance damping in single Ag@SiO(2) nanoparticles.

The optical extinction spectra of single silver nanoparticles coated with a silica shell were investigated in the size range 10-50 nm. Measurements were performed using the spatial modulation spectroscopy technique which permits independent determination of both the size of the metal nanoparticle under study and the width of its localized surface plasmon resonance (LSPR). These parameters can thus be directly correlated at a single particle level for the first time. The results show a linear increase of the width of the LSPR with the inverse diameter in the small size regime (less than 25 nm). For these nanoparticles of well-controlled environment, this can be ascribed to quantum confinement of electrons or, classically, to increase of the electron surface scattering processes. The impact of this effect was measured quantitatively and compared to the predictions by theoretical models.

Field gradient imaging of nanoparticle systems: analysis of geometry and surface coating effects.

In this work we compare the standard imaging of various types of nanoparticles deposited on surfaces by atomic force microscopy (AFM) with a complementary analysis of the same samples by either electrostatic force microscopy (EFM) or magnetic force microscopy (MFM). Experiments were carried out on gold nanoparticles (decahedrons and stars) and two different iron oxide systems: goethite (alpha-FeOOH) and hematite (alpha-Fe(2)O(3)). Regardless of the particular geometry, the EFM signal appears to be stronger on edges or tips of pure gold nanoparticles. Both EFM and MFM experiments were also carried out on iron oxide particles. Apart from the structural analysis, we analyzed the influence of a shell layer deposited on the gold and iron oxide particles, the shell being amorphous SiO(2). Although the silica layer was found to have an insulating effect around the particles, in all cases EFM/MFM measurements could still be performed by the proper choice of the scan lift height (with an eventual slight increase of the sample bias, where applicable).

Influence of silver nanoparticles concentration on the alpha- to beta-phase transformation and the physical properties of silver nanoparticles doped poly(vinylidene fluoride) nanocomposites.

This paper describes the processing of silver nanoparticle doped poly(vinylidene fluoride). The effect of the dopant concentration on the alpha- to beta-phase transformation of the polymer as well as in the morphological, thermal, optical and dielectric properties of the nanocomposites was investigated. Spherical silver nanoparticles were incorporated into the poly(vinylidene fluoride) polymeric matrix by the solvent casting method, with different Ag concentrations. Well-dispersed Ag nanoparticles act as nucleation centers, increasing the degree of crystallinity of the nanocomposites. Homogeneous dispersion of silver nanoparticles is demonstrated through the presence of surface plasmon resonance absorption in the nanocomposites. The alpha- to beta-phase transformation was achieved in the polymer matrix and a maximum of approximately equal to 70% of beta-PVDF was reached at 80 degrees C and a stretching ratio of 400%. The dielectric constant of the nanocomposites increases with increasing metal nanoparticle concentration, up to approximately equal to 26 at 0.020 wt% Ag content. The alpha- to beta-phase transformation affects both the dielectric response and the surface plasmon resonance.

Does conjugation strategy matter? Cetuximab-conjugated gold nanocages for targeting triple-negative breast cancer cells.

The efficient targeting of cancer cells depends on the success of obtaining the active targeting of overexpressed receptors. A very accurate design of nanoconjugates should be done via the selection of the conjugation strategy to achieve effective targeted nanoconjugates. Here, we present a detailed study of cetuximab-conjugated nonspherical gold nanocages for the active targeting of triple-negative breast cancer cells, including MDA-MB-231 and MDA-MB-468. A few different general strategies were selected for monoclonal antibody conjugation to the nanoparticle surface. By varying the bioconjugation conditions, including antibody orientation or the presence of a polymeric spacer or recombinant protein biolinker, we demonstrate the importance of a rational design of nanoconjugates. A quantitative study of gold content via ICP-AES allowed us to compare the effectiveness of cellular uptake as a function of the conjugation strategy and confirmed the active nature of nanoparticle internalization in cancer cells via epidermal growth factor receptor recognition, corroborating the importance of the rational design of nanomaterials for nanomedicine.

Uncertainties and CTV to PTV margins quantitative assessment using cone-beam CT technique in clinical application for prostate, and head and neck irradiation tumours.

PURPOSE To evaluate the magnitude of systematic and random errors from a subset of 100 prostate and 26 head and neck (H&N) cancer patients treated with conventional conformal radiotherapy and using image-guided radiotherapy (IGRT). After treatment, the uncertainties involved and the CTV to PTV margin were evaluated. MATERIAL AND METHODS An Elekta Synergy® linear accelerator was used, taking advantage of 3D on-board computed tomography. IGRT with no-action level (NAL) protocol was applied, reporting the 3D translation and rotation corrections. A statistical study was performed to analyse systematic, random and interobserver uncertainties, and, finally, to obtain the CTV to PTV margins. RESULTS The H&N patients' uncertainties found were smaller than those of prostate patients. The CTV to PTV margins assessed, following the guidelines found in the literature, in the three dimensions of space (right-left, superior-inferior, anterior-posterior) were (5.3, 3.5, 3.2) mm for H&N and (7.3, 7.0, 9.0) mm for prostate cancer treatments. CONCLUSIONS It was found that assessing all the involved uncertainties within radiation treatments was very revealing; their quality improves using IGRT techniques and performing extensive data analysis.