V. M. Castaño

Toxicology of antimicrobial nanoparticles for prosthetic devices

Advances in nanotechnology are producing an accelerated proliferation of new nanomaterial composites that are likely to become an important source of engineered health-related products. Nanoparticles with antifungal effects are of great interest in the formulation of microbicidal materials. Fungi are found as innocuous commensals and colonize various habitats in and on humans, especially the skin and mucosa. As growth on surfaces is a natural part of the Candida spp. lifestyle, one can expect that Candida organisms colonize prosthetic devices, such as dentures. Macromolecular systems, due to their properties, allow efficient use of these materials in various fields, including the creation of reinforced nanoparticle polymers with antimicrobial activity. This review briefly summarizes the results of studies conducted during the past decade and especially in the last few years focused on the toxicity of different antimicrobial polymers and factors influencing their activities, as well as the main applications of antimicrobial polymers in dentistry. The present study addresses aspects that are often overlooked in nanotoxicology studies, such as careful time-dependent characterization of agglomeration and ion release.

A LED-based smart illumination system for studying plant growth

A smart illumination system for greenhouses and growing rooms capable of controlling the quantity and quality of light emitted by a number of LEDs is described. The system uses lamps containing blue and red LEDs programmed to emit various spectra at sixteen different frequencies and ten different pulse widths. The performance of the system is evaluated by determining the effect of pulsed light emission at different frequencies with a pulse width of 50% on tomato plants (Lycopersicon esculentum). The results show that low frequencies (0.1, 1, 10u2009Hz) have higher quantum efficiency in photosystem II compared to higher frequencies (50 and 100u2009kHz) and continuous light. They also show that the electron transport rate decreases when the frequency of pulses increases.

Thermally stimulated luminescence of Mg-doped ZnO Nanophosphors

Nanosized ZnO:Mg phosphors were synthesized through a controlled chemical reaction. X-ray diffraction patterns confirmed that Mg entered in a substitutive way in Zn sites. To investigate their thermoluminescence (TL) properties, some samples were exposed to beta-particle irradiation. The results reported here show that Mg doping improves ZnO TL features that are important for TL dosimetry applications, such as the shape of the glow curve, the temperature at which the maximum TL intensity is observed, and the TL fading and reproducibility. No saturation clues of the TL response as a function of the dose is observed for doses below 1600 Gy.

Hydroxyapatite-Functionalized graphene: a new hybrid nanomaterial

Graphene oxide sheets (GO) were functionalized with hydroxyapatite nanoparticles (nHAp) through a simple and effective hydrothermal treatment and a novel physicochemical process. Microstructure and crystallinity were investigated by Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, X-ray diffraction (XRD), ultraviolet-visible (UV-Vis) absorption spectroscopy, and thermogravimetric analysis (TGA). Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were performed to characterize the morphology of the functionalized material. The resulting novel materials combine the biocompatibility of the nHAp with the strength and physical properties of the graphene.

Electron beam degradation of Ca-A zeolite

Abstract Structural degradation in calcium-A zeolites (Ca-A) subjected to electron beam irradiation was studied in a Transmission Electron Microscope. Several structural changes observed are reported and their possible nature, under the light of the electron beam-matter interaction, is discussed as well.

Final Distribution of CaO and pH Evolution in CaO-treated Clays

The final distribution of the CaO within Ca-treated clays was determined many years after the original treatment, i.e., when the soil-CaO reaction was completed, along with a study of evolution of the corresponding pH. The results reveal that the value of pH accepted in the literature as an indication of the end of the reaction, may not be the actual case.

Thermoluminescence of NaCl:Cu sintered phosphors exposed to beta irradiation

NaCl:Cu pellet-shaped phosphors were synthesized through a sintering process. Some samples were exposed to beta irradiation in order to investigate their thermoluminescence properties and capabilities to be used in detecting and measuring ionizing radiation. The glow curves reveal at least four thermoluminescence peaks below 250°C, and a main one above 300°C when a 5°C/s heating rate is used. The lowest temperature peak vanishes in less than 3 min after irradiation, giving rise to an intense afterglow luminescence, potentially useful for in situ non-thermoluminescence dosimetry, and the next remains for about 3 h, but the high temperature one exhibits no important changes after that time. The thermoluminescence intensity increased as the radiation dose increased in the 0.417–25.0 Gy dose range. Because the position and the remarkable stability of the higher temperature peak, besides the strong afterglow produced by the fast decaying of the lower temperature peak, it is concluded that these phosphors are very suitable candidates to be used in both thermoluminescence and non thermoluminescence dosimetry of ionizing radiation, having advantages over monocrystals of similar composition. The synthesis route here followed can be reproduced in standard college laboratories, and thermoluminescence be measured in home-made systems, allowing design practices for interdisciplinary physics, chemistry electronics, and materials science students.

Fabrication and characterization of new LiF:Eu3+ sintered phosphors exposed to beta particles

Pellet-shaped LiF:Eu3+ phosphors were synthesized by sintering. To improve their thermolumine-scence characteristics, different growth conditions were used. Thermal annealing at 750 °C during 5 h under air atmosphere provided the samples with highest sensitivity. Characteristic glow curves exhibit an absolute maximum centered at 203 °C and another less intense peak between 250 and 300 °C. The first peak has a position very suitable for dosimetry applications. Beta-irradiated samples displayed a thermoluminescence response that increases as the radiation dose increased in the 0.16–42.0 Gy range. A fast fading of<20% occurs in the first 10 s after irradiation, followed by a remarkable stability at room temperature. Computerized glow curve deconvolution of experimental data obtained applying the McKeever method to resolve the individual peaks revealed that the glow curves fit to nine individual peaks. Activation energies were computed by using the initial rise method.