Microporous polymer membranes for light-gated ion transport

In a new report now published in Science Advances, Zongyao Zhou and a team of scientists in chemical engineering and physical science and engineering at the King Abdullah University of Science and Technology in Saudi Arabia ...

Light-gated membranes for ion transport Light-gated ion channels can regulate the transport of ions in living cells to adjust electrical excitability, calcium influx, and other crucial cellular processes. At present, channelrhodopsins are the first and only class of light-gated ion channels identified in biology, and they have received much attention in recent years . The direct use of light-gated channelrhodopsins are limited by the generally minimal chemical and physical stability of the proteins in external environments. Researchers have therefore conducted extensive studies to develop artificial light-gated ion channels for applications across neurobiology, bioelectronics and waste purification.

Artificial light-gated ion channels can be produced in the lab by modifying nanopores with light-responsive functional groups . Conjugated microporous polymers (CMPs) provide a unique class of porous organic materials, as shown in previous work . In this work, Zhou et al synthesized a de novo rigid flexible azobenzene containing monomer (azo-CMP) to achieve the expected light-gated response. The team light-gated structurally well-defined elementary micropores and interconnected them to form smart ion channels in the azo-CMP membrane . The setup is best suited to facilitate photo-switching mechanisms to successfully achieve "on-off-on" photoisomerization for well-regulated ion transport.

Schematic representation of the “bottom-up” design strategy for the construction of artificial light-gated ion channel membrane. (A) Trans-cis-trans reversible isomerization of the synthesized azo-CMP monomer and (B) the elementary pore structure of the azo-CMP membrane. Credit: Science Advances (2022). DOI: 10.1126/sciadv.abo2929 Read more

Azo-CMP membranes. (A) Structure of the synthesized monomer and the mechanism of electropolymerization. (B) CV profiles of the electrochemical oxidation–reduction reaction recorded over 50 CV scan cycles. (C) Membrane thickness as a function of the number of CV cycles. (D) Large-area surface SEM image of the azo-CMP@200-50c membrane on a copper grid. (E) High-magnification SEM image of the surface of the azo-CMP@200-50c membrane. (F) Cross-sectional SEM image of azo-CMP@200-50c membrane on an anodic aluminum oxide (AAO) support. (G) AFM height image of the azo-CMP@200-50c membrane transferred onto a silicon wafer and (H) corresponding height profile of the membrane. (I) AFM image of the azo-CMP@200-50c membrane. RMS, root mean square. (J) AFM image with the peak force quantitative nanomechanical mapping (PFQNM) and (K) the corresponding Young’s modulus profile of the membrane. Credit: Science Advances (2022). DOI: 10.1126/sciadv.abo2929 Read more

Trans-cis-trans reversible isomerization of the azo-CMP@200-50 membrane. (A) Real-time in situ KPFM image of the membrane and (B) corresponding potential profile. (C) UV-vis absorption spectra of trans-to-cis isomerization under UV light and (D) ratio of trans/cis state with UV light irradiation time. (E) UV-vis spectra of cis-to-trans isomerization under vis-light and (F) ratio of trans/cis state with vis-light irradiation time. Credit: Science Advances (2022). DOI: 10.1126/sciadv.abo2929 Read more

Pore-size distribution of azo-CMP@200-50c membrane. (A) The membrane in trans and (B) cis states. (C) Simulated pore-size distribution of the membrane in trans and cis states. A 3D view of the membrane in (D) trans and (E) cis states (free volume in gray and Connolly surface in blue). Credit: Science Advances (2022). DOI: 10.1126/sciadv.abo2929 Read more

Light-gated ion transport of the membranes azo-CMP@200-50c. (A) Schematic diagram of the setup for the tests under electric field. (B) Al3+ conductance changes under alternating UV light and vis-light irradiation calculated on the basis of the data in fig. S28. The insets show the illustration of the controllable ion transport in the ion channels with on and off states. (C) I-V curves of the membranes recorded in 10 mM KCl solution during the trans-to-cis isomerization under UV light. (D) K+-relative conductance changes in successive cycles under alternating UV light and vis-light irradiation. The relative conductance is derived from comparing the conductance of K+ to that of deionized water (fig. S29). (E) Current of common ions recorded in on-state and off-state of the membrane under a voltage of 0.5 V. Note: The current in (E) was normalized by the number of the ion charges based on the data in figs. S28 and S30. (F) K+ and Al3+ permeation rate tested under concentration-driven ion permeation process. The inset shows the details of Al3+ permeation rate. Credit: Science Advances (2022). DOI: 10.1126/sciadv.abo2929 Read more