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Conspectus: Metal nanoparticles are key electrode materials in a variety of electrochemical applications including basic electron-transfer study, electrochemical sensing, and electrochemical surface enhanced Raman spectroscopy (SERS). Metal nanoparticles have also been extensively applied to electrocatalytic processes in recent years due to their high catalytic activity and large surface areas. Because the catalytic activity of metal nanoparticle is often highly dependent on their size, shape, surface ligands, and so forth, methods for examining and better understanding the correlation between particle structure and function are of great utility in the development of more efficient catalytic systems. Despite considerable progress in this field, the understanding of the structure–activity relationships remains challenging in nanoparticle-based electrochemistry and electrocatalysis due to limitations associated with traditional ensemble measurements. One of the major issues is the ensemble averaging of the electrocatalytic response which occurs over a very large number of nanoparticles of various sizes and shapes. Additionally, the electrochemical response can also be greatly affected by properties of the ensemble itself, such as the particle spacing. The ability to directly measure kinetics of electrochemical reactions at structurally well-characterized single nanoparticles opens up new possibilities in many important areas including nanoscale electrochemistry, electrochemical sensing, and nanoparticle electrocatalysis. When a macroscopic electrode is placed in a solution containing redox molecules and metal nanoparticles, random collision and adsorption of nanoparticles occurs at the electrode surface in addition to redox reactions when a suitable potential is present on the electrode. In a special case where particles are catalytically more active than the substrate, the faradaic signals can be greatly amplified on particle surfaces and a steady shift in the baseline current would be expected due to many particles adsorbing on the electrode. Single particle events can be temporally resolved when an ultramicroelectrode (UME) is used as the recording electrode. The use of an UME not only reduces the collision frequency, but also greatly decreases baseline noise, thereby resulting in clear resolution of single collision events. Single particle collision has quickly grown into a popular electroanalytical technique in recent years. Alternatively, one can use nanoelectrodes to immobilize single nanoparticles so that they can be individually studied in electrochemistry and electrocatalysis. Nanoparticle immobilization also allows one to obtain detailed structural information on the same particles and offers enormous potential for developing more comprehensive understanding of the structure–function relationship in nanoparticle-based electrocatalysts. This Account summarizes recent electrochemical experiments of single metal nanoparticles which have been performed by our group using both of these schemes. [ABSTRACT FROM AUTHOR]

Among human body fluids, serum plays a key role for diagnostic tests and, increasingly, for metabolomics analysis. However, the high protein content of serum poses significant challenges for nuclear magnetic resonance (NMR)-based metabolomics studies because it can strongly interfere with metabolite signal detection and quantitation. Although several methods for protein removal have been proposed, including ultrafiltration and organic-solvent-induced protein precipitation, there is currently no standard operating procedure for the elimination of protein from human serum samples. Here, we introduce novel procedures for the removal of protein from serum by the addition of nanoparticles. It is demonstrated how serum protein can be efficiently, cost-effectively, and environmentally friendly removed at physiological pH (pH 7.4) through attractive interactions with silica nanoparticles. It is further shown how serum can be processed with nanoparticles prior to ultrafiltration or organic-solvent-induced protein precipitation for optimal protein removal. After examination of all of the procedures, the combination of nanoparticle treatment and ultrafiltration is found to have a minimal effect on the metabolite content, leading to remarkably clean homo- and heteronuclear NMR spectra of the serum metabolome that compare favorably to other methods for protein removal. [ABSTRACT FROM AUTHOR]

Ru/RuO2core−shell nanoparticles were synthesized by electrochemical method in water without the addition of stabilizers. The zeta potential of the fresh nanoparticles was 30.8 mV in pure water at 25 °C, confirming that the repulsion between the particles is strong enough to stabilize them in aqueous solution. When the Ru/RuO2nanoparticles were loaded on metal oxide supports (CeO2, TiO2and Al2O3), the structure of Ru core and RuO2shell remained unchanged on CeO2support, whereas Ru core was preferred to be oxidized to RuO2on TiO2and Al2O3. The catalytic oxidations of ethanol were chosen to compare the catalytic properties of the Ru/RuO2nanoparticles supported catalysts (our method) with that of Ru catalysts prepared by traditional wet impregnation method. All catalysts prepared by our method showed higher catalytic activities for the catalytic oxidations of ethanol than the Ru catalysts prepared by wet impregnation. [ABSTRACT FROM AUTHOR]

In this paper, two kinds of Ni nanoparticles have been successfully synthesized without and with starch as the "green" protective material and investigated as catalysts for generating hydrogen from ammonia borane (NH3BH3, AB). Experimental investigations have demonstrated that both of the Ni nanoparticles possess high activities fo H2 generation from aqueous solution of AB. However, the catalytic activities of Ni nanoparticles without starch decrease seriously in the course of the lifetime tests. In contrast, the catalytic activities of the Ni nanoparticles with starch almost keep unchanged even after 240 h. Moreover, the XPS results show that the surface of the Ni nanoparticles in starch solution is still metallic Ni even after 240 h, while that in pure water is nickel oxide. This means that starch can successfully keep the Ni nanoparticles in aqueous solution from the oxidation in air. The present efficient, low-cost, and longtime water/air stable Ni catalyst represents a promising step toward the development of AB as a viable on-board hydrogen storage and supply material. [ABSTRACT FROM AUTHOR]

The article discusses the methodology for the synthesis of Gold@Cobalt (Au@Co) magnetic core-shell structured nanoparticles (NPs) through a one-step seeding growth method at room temperature under ambient atmosphere. It mentions that the resultant of the Au@Co NPs present a high catalytic activity and long-term stability for the hydrolytic dehydrogeneration of aqueous AB. It notes that the rational and general method can be easily extended other metallic systems.

Here we report the use of fast-scan cyclic voltammetry (FSCV) to study transient collision and immobilization events of single electro catalytic metal nanoparticles (NPs) on an inert electrode. In this study, a fast, repetitive voltage signal is continuously scanned on an ultramicroelectrode and its faradaic signal is recorded. Electrocatalytically active metal NPs are allowed to collide and immobilize on the electrode resulting in the direct recording of the transient voltammetric response of single NPs. This approach enables one to obtain the transient voltammetric response and electrocatalytic effects of single catalytic NPs as they interact with an inert electrode. The use of FSCV has enabled us to obtain chemical information, which is otherwise difficult to study with previous amperometric methods. [ABSTRACT FROM AUTHOR]

This report presents a fundamental study of nanoparticle transport phenomena in conical-shaped pores contained within glass membranes. The electrophoretic translocation of charged polystyrene (PS) nanoparticles (80- and 160-nm-radius) was investigated using the Coulter counter principle (or "resistive-pulse" method) in which the time-dependent nanopore current is recorded as the nanoparticle is driven across the membrane. Particle translocation through the conical-shaped nanopore results in a direction-dependent and asymmetric triangular-shaped resistive pulse. Because the sensing zone of conical-shaped nanopores is localized at the orifice, the translocation of nanoparticles through this zone is very rapid, resulting in pulse widths of ∼200 μs for the nanopores used in this study. A linear dependence between translocation rate and nanoparticle concentration was observed from 107 to 1011 particles/mL for both 80- and 160-nm-radius particles, and the magnitude of the resistive pulse scaled approximately in proportion to the particle volume. A finite-element simulation based on continuum theory to compute ion fluxes was combined with a dynamic electric force-based nanoparticle trajectory calculation to compute the position- and time-dependent nanoparticle velocity as the nanoparticle translocates through the conical-shaped nanopore. The computational results were used to compute the resistive pulse current—time response for conical-shaped pores, allowing comparison between experimental and simulated pulse heights and translocation times. The simulation and experimental results indicate that nanoparticle size can be differentiated based on pulse height, and to a lesser extent based on translocation time. [ABSTRACT FROM AUTHOR]

Steady-state electrochemical responses have been obtained at single Au nanoparticles using Pt nanoelectrodes. A Au single-nanoparticle electrode (SNPE) is constructed by chemically immobilizing a single Au nanoparticle at a SiO2-encapsulated Pt disk nanoelectrode, which was previously modified by an amine-terminated silane. The Au SNPE has been characterized by transmission electron microscopy, underpotential deposition of Cu, and steady-state cyclic voltammetry. It has been found that the presence of a single Au nanoparticle enhances the electron transfer from the Pt nanoelectrode to the redox molecules, and the voltammetric response at the Au SNPE depends on the size of the Au nanoparticle. The Au SNPE has been utilized to examine the oxygen-reduction reaction in a KOH solution to explore the feasibility of measuring the electrocatalytic activity at a single-nanoparticle level. It has been shown that the electrocatalytic activity of single Au nanoparticles can be directly measured using SNPEs, and the electrocatalytic activity is dependent on the size of the Au nanoparticles. This study can help to understand the structure-function relationship in nanoparticle-based electrocatalysis. [ABSTRACT FROM AUTHOR]

We investigate the principle of the open circuit potential (OCP) change upon a partide collision event based on mixed potential theory and confirmed by a mimic experiment in which we studied the changes in the OCP when two different electrodes (Pt and Au) are brought into contact in a soiution that contains some irreversible redox couples. A micrometer-sized Au ultramicroelectrode, when connected in parallel to a Pt micro- or nanoelectrode, showed dearly measurable OCP changes whose magnitude matches well with that predicted by a simplified mixed potential theory for a pair of different electrode materials. On the basis of the study, each electrode establishes a different mixed potential involving two or more half reactions that have different heterogeneous electron transfer kinetics at different electrodes and the OCP changes are very sensitive to the relative ratio of the rate constant of the individual half reaction at different materials. [ABSTRACT FROM AUTHOR]

Here we report a new type of microelectrode sensor for single-cell exocytotic dopamine release. The new microsensor is built by forming a gold-nanoparticle (AuNP) network on a carbon fiber microelectrode. First a gold surface is obtained on a carbon fiber microdisk electrode by partially etching away the carbon followed by electrochemical deposition of gold into the pore. The gold surface is chemically functionalized with a sol-gel silicate network derived from (3-mercaptopropyl)trimethoxysilane (MPTS). A AuNP network is formed by immobilizing Au nanoparticles onto the thiol groups in the sol-gel silicate network The AuNP-network inicroelectrode has been charactenzed by scanning electron microscopy (SEM) and steady-state voltammetry. The AuNP-network microelectrode has been used for amperometric detection of exocytotic dopamine secretion from individual pheochromocytoma (PC12) cells. The results show significant differences in the lthwtic peak parameters including shorter rise time, decay time, and half-width as compared to a bare carbon fiber electrode equivalent. These results indicate AuNP-network microelectrodes possess an excellent sensing activity for single-cell exocytotic catecholamine release, specifically dopamine. Moreover, key advantageous properties inherent to bare carbon fiber microelectrodes (i.e., rigidity, flexibility, and small size) are maintained in addition to an observed prolonged shelf life stability and resistance to cellular debris fouling and dopamine polymerization. [ABSTRACT FROM AUTHOR]

An efficient and reusable Cu2O/PPh3/TBAB (n-Bu4NBr) system for the cross-coupling reactions of aryl and heteroaryl halides with terminal alkynes has been developed. Four types of Cu2O, including bulky Cu2O, cubic Cu2O nanoparticles, octahedral Cu2O nanoparticles, and spherical Cu2O nanoparticles, were examined, and the octahedral Cu2O nanoparticles were found to be the most effective catalyst for the reaction. In the presence of the octahedral Cu2O nanoparticles, PPh3, and TBAB, a variety of aryl and heteroaryl halides were reacted with alkynes including alkynols smoothly in moderate to good yields. Noteworthy is that the Cu2O/PPh3/TBAB system can be recovered and reused several times without loss of any activities. [ABSTRACT FROM AUTHOR]

A combination of Cu2O nanoparticles with P(o-tol)3 shows highly catalytic activity for the Stille cross-coupling reaction. A series of copper catalysts and ligands were evaluated, and Cu20 nanoparticles combined with P(o-tol)3 provided the best results. In the presence of Cu2O nanoparticles and P(o-tol)3, a variety of aryl halides including aryl chlorides underwent the Stille reaction with organotins smoothly in moderate to excellent yields using inexpensive TBAB (n-Bu4NBr) as the medium. It is noteworthy that the Cu2O/P(o-tol)3/TBAB system can be recovered and reused at least three times without any loss of catalytic activity among the reactions of aryl iodides and activated aryl bromides. [ABSTRACT FROM AUTHOR]