Light-induced correlated ion transport

An “on/off” functionality of a nanopore or channel is critical to control ion transport. In this issue, Chen et al.2Chen F. Gu Z. Zhao C. Y. Jiang X. He al.Ionic Conductance Oscillations in Sub-Nanometer Pores Probed by Optoelectronic Control. Matter, 2021Google Scholar report the elegant use light as trigger induce ionic Coulomb blockade single-layer sub-nanoporous MoS2. Light-induced surface charge phenomenon fast and reversible making it promising technique probe charged Nanofluidics—referring study fluids confined nanoscale environments—is an interdisciplinary research field engaging engineers scientists from diverse backgrounds disciplines. During last two decades, many experimental, computational, theoretical studies have not only provided new deeper perspectives on physics nanofluidics but also impacted societally important areas such energy, water, their nexus, health.1Faucher S. Aluru N. Bazant M.Z. Blankschtein D. Brozena A.H. Cumings J. de Souza J.P. Elimelech M. Epsztein R. Fourkas J.T. al.Critical Knowledge Gaps Mass Transport through Single-Digit Nanopores: A Review Perspective.J. Phys. Chem. 2019; 123: 21309-21326Crossref Scopus (132) Google recent years, has focused creating synthetic analogs naturally existing channels pores using these nanofluidic platforms understand nature. One particular platform that received significant attention nanopores 2D materials. While water transport nanoporous materials been studied, extension demonstrate selective gated sub-nanometer pores. Typically, external gate—akin gate field-effect transistor—is used nanopore. alternative approach nanopore, often accomplished attaching functional groups surface. Variable wall can play role widely electronic counterpart. approach, which introduce manner, light. The requires with bandgap. Single-layer MoS2 material bandgap ∼1.8 eV, suggesting be tuned instead electrode. issue very demonstrating light-induced current modulation pores; i.e., when incident device, increased turned off, reverted back original value. increase selectivity reported density increases. question arises origin due Prior work silicon nitride nanopores3Di Fiori Squires A. Bar Gilboa T. Moustakas T.D. Meller translocation dynamics solid-state nanopores.Nat. Nanotechnol. 2013; 8: 946-951Crossref PubMed (133) shown visible induces negative density. presence light, electrons are excited ground state across create negatively dangling bonds. densities ∼1 C/m2 additional contributions current, electroosmotic flow. case MoS2, electron-hole pairs generated defects trap photoexcited holes, thereby shifting Fermi level closer conduction band. As mobile move close surface, becomes more charged.4Graf Lihter Unuchek Sarathy Leburton Kis al.Light-Enhanced Blue Energy Generation Using Nanopores.Joule. 3: 1549-1564Abstract Full Text PDF (76) reversible, powerful measured (IPd) function illuminating power (Pd), IPd=I(ΔV,Pd), fixing transmembrane bias (ΔV). pores, IPdexhibits oscillatory behavior increasing effects laser-induced heating. Larger diameter (greater than 1.4 nm) exhibit linear variation Clearly, is, what playing causes induced light? attribute oscillations blockade. Analogous where conductance lower at smaller applied biases, single-ion measurements pore current-voltage characteristics non-linear voltage gap for low bias.5Feng Liu K. Graf Dumcenco Di Ventra Radenovic Observation Mater. 2016; 15: 850-855Crossref (118) There least possible mechanisms observed. First, strong ions opposite polarity occupy region reservoirs weakly coupled because Coulombic interactions. If charged, cations reservoir feel repulsion already mouth. Similarly, anions strongly repelled These interactions, combined electrostatic interactions between charges give rise weak coupling phenomena.6Krems Ionic nanopores.J. Condens. Matter. 25: 065101Crossref (29) Second, demonstrated considering forming tight bound pairs—referred Bjerrum pairing ions—and occurring via Onsager’s Wien effect7Onsager L. Deviations Ohm’s Law Weak Electrolytes.J. 1934; 2https://doi.org/10.1063/1.1749541Crossref (904) Scholar,8Kavokine Marbach Siria Bocquet fractional effect.Nat. 14: 573-578Crossref (26) Scholar—where break up giving conduction. Fractional effect long nanotubes (alternatively, slits used) electric may strong. al.,2Chen attributed multi-cation occupied region, cannot completely ruled out even though stronger pairs. Depending multiple (three possibly depending chemistry [see Figure 1]) found dehydration role. repel located nanopore/reservoir interface blocked highly correlated mechanism, bias. Subsequent happens again filled cations. This light-induced, mechanism explains number issues, however, still remain open. exact nature correlations, timescales associated its connection time period oscillations, dynamic life times among issues need further explored. al.’s2Chen certainly opens opportunities detailed Finally, relied voltage, ligand, mechanosensitivity, temperature, gating currents. Translating into active area research. demonstrates cation gate. Cation activated existed nature—for example, channelrhodopsins9Harz H. Hegemann P. Rhodopsin-Regulated Calcium Currents Chlamydomonas.Nature. 1991; 351: 489-491Crossref (195) containing light-isomerizable chromophores undergo conformational change upon absorbing photon opening conduct sodium, potassium, proton, etc. transport, different. It will interesting change-driven other pathway attach chemical mouth opportunity anion Naturally channelrhodopsins exist.10Govorunova E.G. Sineshchekov O.A. Janz Spudich J.L. Natural light-gated channels: family microbial rhodopsins advanced optogenetics.Science. 2015; 349: 647-650Crossref (352) absence closed, open chloride, bromide, fluoride, iodide. probed optoelectronic controlChen al.MatterJune 17, 2021In BriefWith we observe oscillation under confinement, echoing key feature Molecular simulations reveal bindings multi-ion Full-Text Open Archive