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A non-noble metal based 3D porous electrocatalyst is prepared by self-assembly of the liquid-exfoliated single-layer CoAl-layered double hydroxide nanosheets (CoAl-NSs) onto 3D graphene network, which exhibits higher catalytic activity and better stability for electrochemical oxygen evolution reaction compared to the commercial IrO2 nanoparticle-based 3D porous electrocatalyst.

Reactive oxygen and nitrogen species (ROS and RNS) produced by macrophages are essential for protecting a human body against bacteria and viruses. Micrometer-sized electrodes coated with Pt black have previously been used for selective and sensitive detection of ROS and RNS in biological systems. To determine ROS and RNS inside macrophages, one needs smaller (i.e., nanometer-sized) sensors. In this article, the methodologies have been extended to the fabrication and characterization of Pt/Pt black nanoelectrodes. Electrodes with the metal surface flush with glass insulator, most suitable for quantitative voltammetric experiments, were fabricated by electrodeposition of Pt black inside an etched nanocavity under the atomic force microscope control. Despite a nanometerscale radius, the true surface area of Pt electrodes was sufficiently large to yield stable and reproducible responses to ROS and RNS in vitro. The prepared nanoprobes were used to penetrate cells and detect ROS and RNS inside macrophages. Weak and very short leaks of ROS/RNS from the vacuoles into the cytoplasm were detected, which a macrophage is equipped to clean within a couple of seconds, while higher intensity oxidative bursts due to the emptying of vacuoles outside persist on the time scale of tens of seconds.amperometry | atomic force microscopy | oxidative stress | electrochemical nanofabrication | intracellular sensor M acrophage cells are essential for the performance of the immune system. Their activation, either under normal biological conditions or by specific biochemical activators in vitro, results in the production of reactive oxygen and nitrogen species (ROS and RNS) and creation of a large number of vacuoles (phagosomes and phagolysosomes; see Fig. 1A and SI Appendix) (1-3). These vacuoles play an important role in phagocytosisa mechanism used by the immune system to remove pathogens and cell debris. A cell (or debris) is engulfed into a vacuole and subjected to an intense oxidative burst (2), and the indigestible debris and excess ROS and RNS are subsequently evacuated from the macrophage (Fig. 1B).The changes in oxygen and hydrogen peroxide concentrations during the oxidative burst of a stimulated macrophage cell were detected previously using the scanning electrochemical microscope (4). Extensive studies with amperometric microelectrodes positioned in the cell proximity showed that the basal release is due to a cocktail composed of several ROS and RNS evolving from the primary production of O 2•− and NO (5-8). However, the concept that ROS and RNS released inside phagolysosomes may diffuse across the vacuole membrane and leak in the cell cytoplasm remains controversial (9-12). In fact, NO and the transisomer of protonated peroxynitrite ion are capable of crossing biological membranes due to their lipophilicity (13,14). This underscores the importance of probing for the intracellular presence of ROS and RNS in activated macrophages.For electrochemical measurements inside an activated macrophage one needs nanometer-sized electrode...

Solid-state nanopores have been widely employed in sensing applications from Coulter counters to DNA sequencing devices. The analytical signal in such experiments is the change in ionic current flowing through the orifice caused by the large molecule or nanoparticle translocation through the pore. Conceptually similar nanopipette-based sensors can offer several advantages including the ease of fabrication and small physical size essential for local measurements and experiments in small spaces. This paper describes the first evaluation of nanopipettes with well characterized geometry for resistive-pulse sensing of Au nanoparticles (AuNP), nanoparticles coated with an allergen epitope peptide layer, and AuNP–peptide particles with bound antipeanut antibodies (IgY) on the peptide layer. The label-free signal produced by IgY-conjugated particles was strikingly different from those obtained with other analytes, thus suggesting the possibility of selective and sensitive resistive-pulse sensing of antibodies.

Potassium (K) metal anodes suffer from a challenging problem of dendrite growth. Here, it is demonstrated that a tailored current collector will stabilize the metal plating–stripping behavior even with a conventional KPF6‐carbonate electrolyte. A 3D copper current collector is functionalized with partially reduced graphene oxide to create a potassiophilic surface, the electrode being denoted as rGO@3D‐Cu. Potassiophilic versus potassiophobic experiments demonstrate that molten K fully wets rGO@3D‐Cu after 6 s, but does not wet unfunctionalized 3D‐Cu. Electrochemically, a unique synergy is achieved that is driven by interfacial tension and geometry: the adherent rGO underlayer promotes 2D layer‐by‐layer (Frank–van der Merwe) metal film growth at early stages of plating, while the tortuous 3D‐Cu electrode reduces the current density and geometrically frustrates dendrites. The rGO@3D‐Cu symmetric cells and half‐cells achieve state‐of‐the‐art plating and stripping performance. The symmetric rGO@3D‐Cu cells exhibit stable cycling at 0.1–2 mA cm−2, while baseline Cu prematurely fails when the current reaches 0.5 mA cm−2. The half‐cells cells of rGO@3D‐Cu (no K reservoir) are stable at 0.5 mA cm−2 for 10 000 min (100 cycles), and at 1 mA cm−2 for 5000 min. The baseline 3D‐Cu, planar rGO@Cu, and planar Cu foil fails after 5110, 3012, and 1410 min, respectively.

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Measuring electrochemical activities of nanomaterials is critical for creating novel catalysts, for developing ultrasensitive sensors, and for understanding fundamental nanoelectrochemistry. However, traditional electrochemical methods measure a large number of nanoparticles, which wash out the properties of individual nanoparticles. We report here a study of transient electrochemical oxidation of single Ag nanoparticles during collision with an electrode and voltammetry of single nanoparticles immobilized on the electrode using a plasmonic-based electrochemical current microscopy. This technique images both electrochemical reaction and size of the same individual nanoparticle, enabling quantitative examination of size-dependent electrochemical activities at single nanoparticle level. The imaging capability further allows detection of the reaction kinetics of each individual nanoparticle and analysis of the average behaviors of multiple nanoparticles. The average kinetics and size dependence can be accurately described by the Tafel equation, but there is a large variability between different nanoparticles, which underscores the importance of single nanoparticle analysis.

Molybdenum (Mo)-based compounds with properly engineered nanostructures usually possess improved reversible lithium storage capabilities, which offer great promise to boost the performance of lithium-ion batteries (LIBs). Nevertheless, a lack of efficient and high-yield methods for constructing rational nanostructures has largely restricted the application of these potentially important materials. Herein we demonstrate a metal-organic frameworks (MOFs) mediated strategy to successfully synthesize a series of one-dimensional Mo-based/carbon composites with distinct nanostructures. In this process, starting from well-designed MoO nanorods, the crystal control growth is first proposed that a layer of MOFs is achieved to be controllably grown on surfaces of MoO, forming an obvious core-shell structure, and then the adopted precursor can be in situ transformed into MoO or MoC which are both well confined in conductive porous carbons through direct carbonization at different temperatures, where the MOFs shell serve as both carbon sources and the reactant to react with MoO simultaneously. Benefiting from this design, all optimized products exhibit enhanced electrochemical performances when evaluated as anode materials for LIBs, especially the hollow MoO/C and core-shell MoC/C electrodes, show best reversible capacities up to 810 and 530 mAh g even after 600 cycles at a current density of 1 A g, respectively. So this work may broaden the application of MOFs as a kind of coating materials and elucidates the attractive lithium storage performances of molybdenum-based compounds.