Seong Jung Kwon

Skeletal Octahedral Nanoframe with Cartesian Coordinates via Geometrically Precise Nanoscale Phase Segregation in a Pt@Ni Core–Shell Nanocrystal

Catalytic properties of nanoparticles can be significantly enhanced by controlling nanoscale alloying and its structure. In this work, by using a facet-controlled Pt@Ni core-shell octahedron nanoparticle, we show that the nanoscale phase segregation can have directionality and be geometrically controlled to produce a Ni octahedron that is penetrated by Pt atoms along three orthogonal Cartesian axes and is coated by Pt atoms along its edges. This peculiar anisotropic diffusion of Pt core atoms along the ⟨100⟩ vertex, and then toward the ⟨110⟩ edges, is explained via the minimum strain energy for Ni-Ni pair interactions. The selective removal of the Ni-rich phase by etching then results in structurally fortified Pt-rich skeletal PtNi alloy framework nanostructures. Electrochemical evaluation of this hollow nanoframe suggests that the oxygen reduction reaction (ORR) activity is greatly improved compared to conventional Pt catalysts.

Characterization and electrocatalytic properties of Prussian blue electrochemically deposited on nano-Au/PAMAM dendrimer-modified gold electrode

Gold electrode was modified with 3-mercaptopropionic acid (MPA) and further reacted with poly(amidoamine) (PAMAM) dendrimer (generation 4.0) then attached the nano-Au to obtain films on which Prussian blue (PB) was electrochemically deposited to afford much wider pH adaptive range, much better electrochemical stability and excellent electrochemical response. The microstructure and electrochemical behavior of Au/MPA/PAMAM/nano-Au/PB electrode were investigated by scanning electron microscopy (SEM) and cyclic voltammetry. The electrochemical response of the Au/MPA/PAMAM/nano-Au/PB-modified electrode for the electrocatalytic reduction of hydrogen peroxide was investigated, and it was found that the sensitivity as well as the corresponding detection limits were improved as compared to the voltammetric response of a Au/PB-modified electrode and Au/MPA/PAMAM/PB electrode. Based on this, a new electrochemical sensor for determination of hydrogen peroxide has been developed.

An electrochemical immunosensor using ferrocenyl-tethered dendrimer

We report here an enzyme-amplified, sandwich-type immunosensor for detecting the biospecific interaction between an antibody and antigen using redox mediation. We employed biotin/anti-biotin IgG as a model immunosensing pair. Partially ferrocenyl-tethered dendrimer (Fc-D), whose ferrocene moiety acts as a redox mediator, was immobilized to the electrode surface by covalent binding between the dendrimer amines and the carboxylic acids of a self-assembled monolayer. The unreacted amines of the immobilized Fc-D were modified with biotin groups to allow the specific binding of goat anti-biotin IgG. Rabbit anti-goat IgG-conjugated alkaline phosphatase was bound to goat anti-biotin IgG to catalyze conversion of p-aminophenyl phosphate monohydrate to p-aminophenol. This product is oxidized to quinoimide by the reduction of ferrocenium back to ferrocene, producing an electrocatalytic anodic current. Cyclic voltammograms and surface plasmon resonance experiments showed that the binding of nonspecific proteins is not significant on the biotinylated Fc-D surface. We also examined the change in peak current according to the concentration of anti-biotin IgG and found that the detection range of this immunosensing scheme is between 0.1 and 30 microg mL(-1).

One-pot synthesis of ultralong coaxial Au@Pt nanocables with numerous highly catalytically active perpendicular twinning boundaries and Au@Pt core–shell bead structures

Ultralong coaxial Au@Pt nanocables prepared by one-pot synthesis exhibit excellent electrocatalytic activity due to structural features of (1) numerous twinning boundaries and (2) lattice mismatch between the core and the shell.

Axially twinned nanodumbbell with a Pt bar and two Rh@Pt balls designed for high catalytic activity

A fail-proof synthetic strategy has been developed for a multiply twinned dumbbell-shaped Rh@Pt nanostructure, which exhibits a superior electrocatalytic activity for methanol oxidation reaction. The unusually high electrocatalytic activity has been attributed to the synergistic effects of crystal twinning and core-shell structure.

Twinning boundary-elongated hierarchical Pt dendrites with an axially twinned nanorod core for excellent catalytic activity

Twinning boundary-elongated hierarchical Pt nanostructures with excellent electrocatalytic activity were prepared by using axially twinned Pt3Ni nanorods as the platform for epitaxial transfer of a twinned crystal structure. The high electrocatalytic activity of the hierarchical nanostructures results from the synergistic effects of lattice mismatch between the Pt3Ni core and the Pt shell and the elongated twinning boundary.

Combined Blip and Staircase Response of Ascorbic Acid-Stabilized Copper Single Nanoparticle Collision by Electrocatalytic Glucose Oxidation.

The current response of the collision of ascorbic acid-stabilized copper (Cu) single nanoparticles (NPs) on a gold (Au) ultramicroelectrode (UME) surface was observed by using an electrocatalytic amplification method. Here, the glucose oxidation electrocatalyzed by oxidized Cu NPs was used as the indicating reaction. In this system, the NP collision signals were obtained simultaneously by both direct particle electrolysis and electrocatalytic amplification. For example, when the applied potential was high enough for Cu NP oxidation, a blip response combined with a staircase response was observed as a current signal. The blip part in the single Cu NP collision signal indicates the self-oxidation of a Cu NP, and the staircase part indicates the steady-state electrocatalytic reaction by oxidized Cu NP.

One-pot synthesis of a highly active, non-spherical PdPt@Pt core–shell nanospike electrocatalyst exhibiting a thin Pt shell with multiple grain boundaries

Co-decomposition of Pd and Pt precursors in the presence of trioctylphosphine and stearic acid gives a unique non-spherical PdPt@Pt core–shell nanospike with multiple grain boundaries in a facile one-pot synthesis. The difference in the metal–P bond strengths causes the disparate precursor decomposition kinetics, which in turn positions the Pt content on the nanoparticle surface. The core–shell composition, crystallinity, and shell thickness are conveniently controlled by simple variations in the amount of precursors and surfactants. The PdPt@Pt core–shell nanospike shows a high electrocatalytic activity toward methanol oxidation reaction. The excellent catalytic performance seems to originate from (1) the existence of multiple, surface energy-elevating grain boundaries, (2) roughened surface, and (3) lattice mismatch between the core and shell.

Purification, crystallization and preliminary X-ray diffraction analysis of enoyl-acyl carrier protein reductase (FabK) from Streptococcus mutans strain UA159

A triclosan-resistant flavoprotein termed FabK is the sole enoyl-acyl carrier protein reductase in Streptococcus pneumoniae and Streptococcus mutans. In this study, FabK from S. mutans strain UA159 was overexpressed in Escherichia coli, purified and crystallized. Diffraction data were collected to 2.40 Å resolution using a synchrotron-radiation source. The crystal belonged to space group P6(2), with unit-cell parameters a = b = 105.79, c = 44.15 Å. The asymmetric unit contained one molecule, with a corresponding V(M) of 2.05 Å(3) Da(-1) and a solvent content of 39.9%.

Various Current Responses of Single Silver Nanoparticle Collisions on a Gold Ultramicroelectrode Depending on the Collision Conditions

Collisions of silver nanoparticles (NPs) with a more electrocatalytic gold or platinum ultramicroelectrode (UME) surface have been observed by using an electrochemical method. Depending on the applied potential to the UME, the current response to the collision of Ag NPs on the UME resulted in various shape changes. A staircase decrease, a blip decrease, and a blip increase of the hydrazine oxidation current were obtained at an applied potential of 0.33, 0.80, and 1.3 V, respectively. Different collision behaviors of Ag NPs on the UME surface were suggested for each shape of current response. Ag NP attachment, which hindered the diffusion flux to the UME, caused a staircase decrease of the electrocatalytic current. Instantaneous blocking of the hydrazine oxidation by Ag NP collision and, following recovery of the current by means of oxidation of Ag NP, caused a blip decrease of the electrocatalytic current. The formation of a higher oxidation state of Ag on the Ag NP and its electrocatalytic hydrazine oxidation resulted in a blip increase of the electrocatalytic current. The analysis of the current response of a single NP collision experiment can be a useful tool to understand the various behaviors of NPs on the electrode surface.