The nuclear pore complex (NPC) solely mediates molecular transport between the nucleus and cytoplasm of a eukaryotic cell to play important biological and biomedical roles. It, however, is not well understood chemically how this biological nanopore selectively and efficiently transports various substances including small molecules, proteins, and RNAs by using transport barriers that are rich in highly disordered repeats of hydrophobic phenylalanine and glycine intermingled with charged amino acids. Herein, we employ scanning electrochemical microscopy to image and measure the high permeability of NPCs to small redox molecules. The effective medium theory demonstrates that the measured permeability is controlled by diffusional translocation of probe molecules through water-filled nanopores without steric or electrostatic hindrance from hydrophobic or charged regions of transport barriers, respectively. The permeability of NPCs, however, is lowered by a low millimolar concentration of Ca 2+ , which can interact with anionic regions of transport barriers to alter their spatial distributions within the nanopore. We employ atomic force microscopy to confirm that transport barriers of NPCs are dominantly recessed (~80%) or entangled (~20%) at the high Ca 2+ level in contrast to authentic populations of entangled (~50%), recessed (~25%), and "plugged" (~25%) conformations at a physiological Ca 2+ level of sub-micromolar. We propose a model for synchronized Ca 2+ effects on the conformation and permeability of NPCs, where transport barriers are viscosified to lower permeability. Significantly, this result supports a hypothesis that the functional structure of transport barriers is maintained not only by their hydrophobic regions, but also by charged regions.

Nickel–iron oxyhydroxides (Ni1−xFexOOH) are non-precious metal electrocatalysts for the oxygen evolution reaction (OER) that have high efficiency in alkaline media.

The electrochemically-formed In0–In2O3 composite changes the selectivity of CO2 reduction on In from formate to CO at relatively low overpotentials.

Layered double hydroxide (LDH) and amorphous nickel−iron (oxy)hydroxides (Ni 1−x Fe x OOH) are emerging catalysts for the electrochemical oxygen evolution reaction (OER). It is still unresolved if the layered twodimensional (2D) structure allows for active catalytic sites to exist below the traditional electrode/electrolyte interface. Herein, we utilized the surface interrogation mode of scanning electrochemical microscopy (SI-SECM) to directly measure active site densities in situ. We determined that Ni 0.8 Fe 0.2 OOH LDH showed a 10-fold increase in the active site density compared to rock salt Ni 0.8 :Fe 0.2 oxide, giving direct evidence that water and hydroxide in the interlayer are able to create stable Ni IV /Fe IV active species at layers below the electrode/ electrolyte interface. This result suggests that electrolyte permeability of the 2D LDH structure is a major contributor for its increased catalytic activity. Amorphous Ni 0.8 :Fe 0.2 oxide also exhibits an anomalously high active site density and higher activity than Ni 0.8 Fe 0.2 OOH LDH.

Scanning electrochemical microscopy (SECM) enables high-resolution imaging by examining the amperometric response of an ultramicroelectrode tip near a substrate. Spatial resolution, however, is compromised for non-flat substrates, where distances from a tip far exceed the tip size to avoid artifacts caused by the tip-substrate contact. Herein, we propose a new imaging mode of SECM based on real-time analysis of approach curve to actively control nanoscale tip-substrate distances without contact. The power of this software-based method is demonstrated by imaging an insulating substrate with step edges using standard instrumentation without combination of another method for distance measurement, e.g., atomic force microscopy. An ~500 nm-diameter Pt tip approaches down to ~50 nm from upper and lower terraces of a 500 nm-height step edge, which are located by real-time theoretical fitting of experimental approach curve to ensure the lack of electrochemical reactivity. The tip approach to step edge can be terminated at <20 nm prior to the tip-substrate contact as soon as the theory deviates from the tip current, which is analyzed numerically afterward to locate the inert edge. The advantageous local adjustment of tip height and tip current at the final point of tip approach distinguishes the proposed imaging mode from other modes based on standard instrumentation. In addition, the glass sheath of Pt tip is thinned to ~150 nm to rarely contact the step edge, which is unavoidable and instantaneously detected as an abrupt change in the slope of approach curve to prevent the damage of fragile nanotip.