XPS represents a powerful tool for investigation of chemistry involved in chemical sensors, as analytes and recognition elements interact at a device surface, the region analyzed by the spectroscopic technique.
A method for the aqueous synthesis of stable and biocompatible citrate-coated palladium nanoparticles (PdNPs) in the size range comparable to natural enzymes (4–8 nm) has been developed. The toxicological profile of PdNPs was assessed by different assays on several cell lines demonstrating their safety in vitro also at high particle concentrations. To elucidate their cellular fate upon uptake, the localization of PdNPs was analyzed by Transmission Electron Microscopy (TEM). Moreover, crucial information about their intracellular stability and oxidation state was obtained by Sputtering-Enabled Intracellular X-ray Photoelectron Spectroscopy (SEI-XPS). TEM/XPS results showed significant stability of PdNPs in the cellular environment, an important feature for their biocompatibility and potential for biomedical applications. On the catalytic side, these PdNPs exhibited strong and broad antioxidant activities, being able to mimic the three main antioxidant cellular enzymes, i.e., peroxidase, catalase, and superoxide dismutase. Remarkably, using an experimental model of a human oxidative stress-related disease, we demonstrated the effectiveness of PdNPs as antioxidant nanozymes within the cellular environment, showing that they are able to completely re-establish the physiological Reactive Oxygen Species (ROS) levels in highly compromised intracellular redox conditions.
The investigation of the toxicological profile and biomedical potential of nanoparticles (NPs) requires a deep understanding of their intracellular fate. Various techniques are usually employed to characterize NPs upon cellular internalization, including high-resolution optical and electron microscopies. Here, we show a versatile method, named sputtering-enabled intracellular X-ray photoelectron spectroscopy, proving that it is able to provide valuable information about the behavior of metallic NPs in culture media as well as within cells, directly measuring their internalization, stability/degradation, and oxidation state, without any preparative steps. The technique can also provide nanoscale vertical resolution along with semiquantitative information about the cellular internalization of the metallic species. The proposed approach is easy-to-use and can become a standard technique in nanotoxicology/nanomedicine and in the rational design of metallic NPs. Two model cases were investigated: silver nanoparticles (AgNPs) and platinum nanoparticles (PtNPs) with the same size and coating. We observed that, after 48 h incubation, intracellular AgNPs were almost completely dissolved, forming nanoclusters as well as AgO, AgS, and AgCl complexes. On the other hand, PtNPs were resistant to the harsh endolysosomal environment, and only some surface oxidation was detected after 48 h.
Surface doping of nano/mesostructured materials with metal nanoparticles to promote and optimize chemi-transistor sensing performance represents the most advanced research trend in the field of solid-state chemical sensing. In spite of the promising results emerging from metal-doping of a number of nanostructured semiconductors, its applicability to silicon-based chemi-transistor sensors has been hindered so far by the difficulties in integrating the composite metal-silicon nanostructures using the complementary metal-oxide-semiconductor (CMOS) technology. Here we propose a facile and effective top-down method for the high-yield fabrication of chemi-transistor sensors making use of composite porous silicon/gold nanostructures (cSiAuNs) acting as sensing gate. In particular, we investigate the integration of cSiAuNs synthesized by metal-assisted etching (MAE), using gold nanoparticles (NPs) as catalyst, in solid-state junction-field-effect transistors (JFETs), aimed at the detection of NO2 down to 100 parts per billion (ppb). The chemi-transistor sensors, namely cSiAuJFETs, are CMOS compatible, operate at room temperature, and are reliable, sensitive, and fully recoverable for the detection of NO2 at concentrations between 100 and 500 ppb, up to 48 h of continuous operation.
Environmental context. Antimony is an environmental contaminant of increasing concern, due to its growing industrial usage in flame retardants, lead alloys, glass, ceramics and plastics. Here we show, using X-ray absorption spectroscopy, that antimony may be trapped in wetland sediments by reduced sulfur. This finding has implications for the management and remediation of wetlands contaminated with antimony.Abstract. The biogeochemistry of antimony (Sb) in wetland sediments is poorly characterised, despite their importance as contaminant sinks. The organic-rich, reducing nature of wetland sediments may facilitate sequestration mechanisms that are not typically present in oxic soils, where the majority of research to date has taken place. Using X-ray absorption spectroscopy (XAS), we present evidence of antimony speciation being dominated by secondary antimony-sulfur phases in a wetland sediment. Our results demonstrate that, by incorporating a newly developed Sb III -organic sulfur reference standard, linear combination fitting analysis of antimony K-edge XAS spectra and robust statistical assessment of fit quality allows the reliable discrimination of Sb III coordination environments. We found that a contaminated wetland sediment in New South Wales, Australia, contained 57 % of the total antimony as Sb III -phases, with 44 % present as a highly-disordered antimony phase, likely consisting of Sb III complexed by organic sulfur (e.g. thiols) or an amorphous Sb III sulfide (e.g. SbS 3 ). The methodological approach outlined in this study and our identification of the importance of reduced sulfur in sequestering antimony has implications for future research in the area of antimony biogeochemistry, and for the management of both natural and artificial wetlands contaminated with antimony.
In the field of nanomedicine, superparamagnetic nanoparticles are one of the most studied nanomaterials for theranostics. In this study, a one-pot synthesis of magnetic nanoparticles is presented, with an increased control on particle size from 10 to 40 nm. Monitoring of vacuum level is introduced here as a crucial parameter for achieving a fine particle morphology. The magnetic properties of these nanoparticles are highly affected by disorders or mismatches in crystal structure. A prolonged oxidation step is applied to the obtained nanoparticles to transform the magnetic phases into a pure maghemite one, confirmed by high-resolution X-ray photoelectron spectroscopy analysis, by Mössbauer spectrometry and, indirectly, by increased performances in magnetization curves and in relaxation times. Afterward, the attained nanoparticles are transferred into water by a nonderivatized dextran coating. Thermogravimetric analysis confirms that polysaccharide molecules replace oleic acid on the surface by stabilizing the particles in the aqueous phase and culture media. Preliminary in vitro test reveals that the dextran-coated nanoparticles are not passively internalized from the cells. As a proof of concept, a secondary layer of chitosan assures a positive charge to the nanoparticle surface, thus enhancing cellular internalization.
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