Metal–Organic Framework Membrane Nanopores as Biomimetic Photoresponsive Ion Channels and Photodriven Ion Pumps

Tailoring CO2-Activated Ion Nanochannels Using Macrocyclic Pillararenes

Gas-responsive nanochannels have great relevance for applications in many fields. Inspired by CO₂-sensitive ion channels, herein we present an approach for designing solid-state nanochannels that allow controlled regulation of ion transport in response to alternate CO₂/N₂ stimuli. The pillar[5]arene (P5N) bearing diethylamine groups can convert into the water-soluble host P5C, containing cationic tertiary ammonium salt groups after absorbing CO₂. Subsequently, the nanochannel walls are tailored using P5N-based host-guest chemistry. The ion transport rate of K⁺ in the P5N nanochannels under CO₂ was 1.66 × 10^-4 mol h^-1 m^-2, whereas that under N₂ was 7.98 × 10^-4 mol h^-1 m^-2. Notably, there was no significant change to the ion current after eight cycles, which may indicate the stability and repeatability of CO₂-activated ion nanochannels. It is speculated that the difference in ion conductance resulted from the change in wettability and surface charge within the nanochannels in response to the gas stimuli. Achieving CO₂-activated ion transport in solid-state nanochannels opens new avenues for biomimetic nanopore systems and advanced separation processes.

Carbon support tuned electrocatalytic activity of a single-site metal-organic framework toward the oxygen reduction reaction

Metal-organic frameworks (MOFs) possess fantastic features such as structural diversity, tunable accessible pores and atomically dispersed active sites, holding tremendous potential as highly versatile platforms for fabricating single-site catalysts. The electrocatalytic activity of single-site MOFs can be improved and tuned via several approaches; however, the exploitation of different carbon supports to modulate the nature of single active sites in MOFs for electrocatalysis has not been reported. Here, we find that the electrocatalytic activity of single-site MOFs toward the oxygen reduction reaction (ORR) can be tuned by using carbon nanomaterials, i.e., carbon nanotubes and graphene, as supports through MOF-support interactions in the manner of geometric and electronic effects. The introduction of MOF-support interactions not only greatly improves the electrocatalytic performance of MOFs toward the ORR in terms of onset and half-wave potentials and current density, but also alters the reaction pathway of the ORR. This finding provides a new horizon for the design and synthesis of single-site MOFs for electrocatalysis.

Twin Nanopipettes for Real-Time Electrochemical Monitoring of Cytoplasmic Microviscosity at a Single-Cell Level

Cytoplasmic microviscosity (CPMV) plays essential roles in governing the diffusion-mediated cellular processes and has been recognized as a reliable indicator of the cellular response of many diseases and malfunctions. Current CPMV studies are exclusively established by probe-assisted optical methods, which nevertheless necessitate the complicated synthesis and delivery of optical probes into cells and thus the issues of biocompatibility and bio-orthogonality. Using twin nanopipettes integrated with a patch-clamp system, a practical electrochemical single-cell measurement is presented, which is capable of real-time and long-term CPMV detection without cell disruption. Specifically, upon the operation of the twin nanopipettes, the cellular CPMV status, which is correlated to cytoplasmic ionic mobility, could be sensibly transduced via the ionic current passing through the nanosystem. The average CPMV value of HeLa cells was detected as ca. 86 cP. Notably, the correlation between chemotherapy and CPMV alterations makes this approach possible for the real-time and long-term assessment of the evolution of external stimuli, as exemplified by the two natural products taxol and colchicine. Integrated with the patch-clamp setup, this study features the first use of twin nanopipettes for electrochemical CPMV monitoring of single living cells, and it is expected to inspire more interest in the exploitation of dual- and multiple nanopipettes for advanced single-cell analysis.

Target-Dependent Gating of Nanopores Integrated with H-Cell: Toward A General Platform for Photoelectrochemical Bioanalysis

Herein we present a proof-of-concept study of target-dependent gating of nanopores for general photoelectrochemical (PEC) bioanalysis in an H-cell. The model system was constructed upon a left chamber containing ascorbic acid (AA), the antibody modified porous anodic alumina (AAO) membrane separator, and a right chamber placed with the three-electrode system. The sandwich immunocomplexation and the associated enzymatic generation of biocatalytic precipitation (BCP) in the AAO nanopores would regulate the diffusion of AA from the left cell to the right cell, leading to a varied photocurrent response of the ZnInS nanoflakes photoelectrode. Exemplified by fatty-acid-banding protein (FABP) as the target, the as-developed protocol achieved good performance in terms of sensitivity, selectivity, reproducibility, as well as efficient reutilization of the working electrode. On the basis of an H-cell, this work features a new protocol of target-dependent gating-based PEC bioanalysis, which can serve as a general PEC analytical platform for various other targets of interest.

Concomitant Photoresponsive Chiroptics and Magnetism in Metal-Organic Frameworks at Room Temperature

Stimulus-responsive metal-organic frameworks (MOFs) can be used for designing smart materials. Herein, we report a family of rationally designed MOFs which exhibit photoresponsive chiroptical and magnetic properties at room temperature. In this design, two specific nonphotochromic ligands are selected to construct enantiomeric MOFs, {Cu₂(L-mal)₂(bpy)₂(H₂O)·3H₂O}_n (1) and {Cu₂(D-mal)₂(bpy)₂(H₂O)·3H₂O}_n (2) (mal = malate, bpy = 4, 4′ − bipyridine), which can alter their color, magnetism, and chiroptics concurrently in response to light. Upon UV or visible light irradiation, long-lived bpy⁻ radicals are generated via photoinduced electron transfer (PET) from oxygen atoms of carboxylates and hydroxyl of malates to bpy ligands, giving rise to a 23.7% increase of magnetic susceptibility at room temperature. The participation of the chromophores (-OH and -COO⁻) bound with the chiral carbon during the electron transfer process results in a small dipolar transition; thus, the Cotton effects of the enantiomers are weakened along with a photoinduced color change. This work demonstrates that the simultaneous responses of chirality, optics, and magnetism can be achieved in a single compound at room temperature and may open up a new pathway for designing chiral stimuli-responsive materials.