Supersensitive CeOx-based nanocomposite sensor for the electrochemical detection of hydroxyl free radicals.

It is well known that an excess of hydroxyl radicals (˙OH) in the human body is responsible for oxidative stress-related diseases. An understanding of the relationship between the concentration of ˙OH and those diseases could contribute to better diagnosis and prevention. Here we present a supersensitive nanosensor integrated with an electrochemical method to measure the concentration of ˙OH in vitro. The electrochemical sensor consists of a composite comprised of ultrasmall cerium oxide nanoclusters (<2 nm) grafted to a highly conductive carbon deposited on a screen-printed carbon electrode (SPCE). Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to analyze the interaction between cerium oxide nanoclusters and ˙OH. The CV results demonstrated that this electrochemical sensor had the capacity of detecting ˙OH with a high degree of accuracy and selectivity, achieving a consistent performance. Additionally, EIS results confirmed that our electrochemical sensor was able to differentiate ˙OH from hydrogen peroxide (H2O2), which is another common reactive oxygen species (ROS) found in the human body. The limit of detection (LOD) observed with this electrochemical sensor was of 0.6 µM. Furthermore, this nanosized cerium oxide-based electrochemical sensor successfully detected in vitro the presence of ˙OH in preosteoblast cells from newborn mouse bone tissue. The supersensitive electrochemical sensor is expected to be beneficially used in multiple applications, including medical diagnosis, fuel-cell technology, and food and cosmetic industries.

Detection Technologies for Reactive Oxygen Species: Fluorescence and Electrochemical Methods and Their Applications.

Reactive oxygen species (ROS) have been found in plants, mammals, and natural environmental processes. The presence of ROS in mammals has been linked to the development of severe diseases, such as diabetes, cancer, tumors, and several neurodegenerative conditions. The most common ROS involved in human health are superoxide (O2•-), hydrogen peroxide (H2O2), and hydroxyl radicals (•OH). Organic and inorganic molecules have been integrated with various methods to detect and monitor ROS for understanding the effect of their presence and concentration on diseases caused by oxidative stress. Among several techniques, fluorescence and electrochemical methods have been recently developed and employed for the detection of ROS. This literature review intends to critically discuss the development of these techniques to date, as well as their application for in vitro and in vivo ROS detection regarding free-radical-related diseases. Moreover, important insights into and further steps for using fluorescence and electrochemical methods in the detection of ROS are presented.

Self-assembly of noble metal monolayers on transition metal carbide nanoparticle catalysts.

We demonstrated the self-assembly of transition metal carbide nanoparticles coated with atomically thin noble metal monolayers by carburizing mixtures of noble metal salts and transition metal oxides encapsulated in removable silica templates. This approach allows for control of the final core-shell architecture, including particle size, monolayer coverage, and heterometallic composition. Carbon-supported Ti(0.1)W(0.9)C nanoparticles coated with Pt or bimetallic PtRu monolayers exhibited enhanced resistance to sintering and CO poisoning, achieving an order of magnitude increase in specific activity over commercial catalysts for methanol electrooxidation after 10,000 cycles. These core-shell materials provide a new direction to reduce the loading, enhance the activity, and increase the stability of noble metal catalysts.

Reverse Water-Gas Shift on Interfacial Sites Formed by Deposition of Oxidized Molybdenum Moieties onto Gold Nanoparticles.

We show that MoO(x)-promoted Au/SiO2 catalysts are active for reverse water-gas shift (RWGS) at 573 K. Results from reactivity measurements, CO FTIR studies, Raman spectroscopy, and X-ray absorption spectroscopy (XAS) indicate that the deposition of Mo onto Au nanoparticles occurs preferentially on under-coordinated Au sites, forming Au/MoO(x) interfacial sites active for reverse water-gas shift (RWGS). Au and AuMo sites are quantified from FTIR spectra of adsorbed CO collected at subambient temperatures (e.g., 150-270 K). Bands at 2111 and 2122 cm(-1) are attributed to CO adsorbed on under-coordinated Au(0) and Au(δ+) species, respectively. Clausius-Clapeyron analysis of FTIR data yields a heat of CO adsorption (ΔH(ads)) of -31 kJ mol(-1) for Au(0) and -64 kJ mol(-1) for Au(δ+) at 33% surface coverage. Correlations of RWGS reactivity with changes in FTIR spectra for samples containing different amounts of Mo indicate that interfacial sites are an order of magnitude more active than Au sites for RWGS. Raman spectra of Mo/SiO2 show a feature at 975 cm(-1), attributed to a dioxo (O═)2Mo(-O-Si)2 species not observed in spectra of AuMo/SiO2 catalysts, indicating preferential deposition of Mo on Au. XAS results indicate that Mo is in a +6 oxidation state, and therefore Au and Mo exist as a metal-metal oxide combination. Catalyst calcination increases the quantity of under-coordinated Au sites, increasing RWGS activity. This strategy for catalyst synthesis and characterization enables quantification of Au active sites and interfacial sites, and this approach may be extended to describe reactivity changes observed in other reactions on supported gold catalysts.

Stabilization of copper catalysts for liquid-phase reactions by atomic layer deposition.

Atomic layer deposition (ALD) of an alumina overcoat can stabilize a base metal catalyst (e.g., copper) for liquid-phase catalytic reactions (e.g., hydrogenation of biomass-derived furfural in alcoholic solvents or water), thereby eliminating the deactivation of conventional catalysts by sintering and leaching. This method of catalyst stabilization alleviates the need to employ precious metals (e.g., platinum) in liquid-phase catalytic processing. The alumina overcoat initially covers the catalyst surface completely. By using solid state NMR spectroscopy, X-ray diffraction, and electron microscopy, it was shown that high temperature treatment opens porosity in the overcoat by forming crystallites of γ-Al2 O3 . Infrared spectroscopic measurements and scanning tunneling microscopy studies of trimethylaluminum ALD on copper show that the remarkable stability imparted to the nanoparticles arises from selective armoring of under-coordinated copper atoms on the nanoparticle surface.