RESUMO
Ion bombardment is an important tool of materials processing, but usually leads to erosion of the surface and significant thickness reductions when thin layers are used. The growing use of polymer thin films in a variety of applications, from coatings and membranes to biomedical and electronic devices, calls for a deeper understanding of the thinning process induced by energetic ions espe-cially for very thin films. Here, thinning and surface morphology changes induced by high-energy ion bombardment in PMMA and PVC thin films were investigated, focusing on the role of the initial thickness of the films and the stopping power of the ions. We used thin films with initial thicknesses varying from 13 to 800 nm, and light and heavy ions as projectiles in the energy range of 2-2000 MeV, where the electronic stopping dominates. Thickness reductions as a function of fluence were monitored and thinning cross sections were extracted from curves. A supralinear scaling between the thinning cross sections and the electronic stopping power of the beams was observed, with a much enhanced thinning efficiency for the swift heavy ions. The scaling with the stopping power dE/dx is almost independent of the initial thickness of the films. At intermediate and large fluences, changes in the physicochemical properties of the irradiated polymers may modulate and decelerate the thinning process of the remaining film. The importance of this secondary process depends on the stopping power and the balance between erosion and the chemical transformations induced by the beam. We also observe a trend for the thinning efficiency to become larger in very thin films. Depending on the type of beam and polymer, this effect is more or less pronounced. PMMA films irradiated with 2 MeV H+ show the most systematic correlation between initial thickness and thinning cross sections, while in PVC films the initial thickness plays a minor role for all investigated beams.
RESUMO
In this work, an intercomparison of sensitization effects produced by gold (GNP) and dextran-coated iron oxide (SPION-DX) nanoparticles in M059J and U87 human glioblastoma cells was performed using 6 MV-photons. Three variables were mapped: the nanoparticle material, treatment concentration, and cell radiosensitivity. For U87, GNP treatments resulted in high sensitization enhancement ratios (SER[Formula: see text] up to 2.04). More modest effects were induced by SPION-DX, but still significant reductions in survival were achieved (maximum SER[Formula: see text] ). For the radiosensitive M059J, sensitization by both NPs was poor. SER[Formula: see text] increased with the degree of elemental uptake in the cells, but not necessarily with treatment concentration. For GNP, where exposure concentration and elemental uptake were found to be proportional, SER[Formula: see text] increased linearly with concentration in both cell lines. For SPION-DX, saturation of sensitization enhancement and metal uptake occurred at high exposures. Fold change in the [Formula: see text] ratios extracted from survival curves are reduced by the presence of SPION-DX but strongly increased by GNPs , suggesting that sensitization by GNPs occurs mainly via promotion of lethal damage, while for SPION-DX repairable damage dominates. The NPs were more effective in eliminating the radioresistant glioblastoma cells, an interesting finding, as resistant cells are key targets to improve treatment outcome.
Assuntos
Glioblastoma , Nanopartículas Metálicas , Radiossensibilizantes , Glioblastoma/radioterapia , Ouro/farmacologia , Humanos , Nanopartículas Magnéticas de Óxido de Ferro , Fótons , Radiossensibilizantes/farmacologiaRESUMO
Excited-state intramolecular proton transfer (ESIPT) is a particularly well known reaction that has been very little studied in magnetic environments. In this work, we report on the photophysical behavior of a known ESIPT dye of the benzothiazole class, when in solution with uncoated superparamagnetic iron oxide nanoparticles, and when grafted to silica-coated iron oxide nanoparticles. Uncoated iron oxide nanoparticles promoted the fluorescence quenching of the ESIPT dye, resulting from collisions during the lifetime of the excited state. The assembly of iron oxide nanoparticles with a shell of silica provided recovery of the ESIPT emission, due to the isolation promoted by the silica shell. The silica network gives protection against the fluorescence quenching of the dye, allowing the nanoparticles to act as a bimodal (optical and magnetic) imaging contrast agent with a large Stokes shift.
RESUMO
A simple one-step method based on the sputtering deposition of Ni nanoparticles (NP) has been developed for the production of magnetic biocatalysts, avoiding the complications and drawbacks of methods based on chemical functionalisation or coating of magnetic NP. This new technique provided high levels of recovery, reusability and catalytic activity for the lipase-Ni biocatalyst.