Fluorescence Microscopic Investigations of Molecular Dynamics in Self‐Assembled Nanostructures

Abstract

Many analytical methods employ self‐assembled nanostructured materials as chemical recognition media. Molecular permeation through these materials exhibits unique selectivity owing to nanoconfinement‐induced enhancement of permeant‐nanostructure interactions. This Personal Account introduces our efforts to investigate the detailed dynamics of single or a small number of molecules in nanostructured materials. We developed new experimental and analysis approaches built upon laser‐based fluorescence microscopy to measure the detailed translational and orientational dynamics of molecules diffusing in horizontally‐oriented, cylindrical nanostructures, including surfactant micelles, silica mesopores, block copolymer microdomains, and bolaamphiphile‐based organic nanotubes. Our studies clarified nanoscale details on the structural/chemical heterogeneity of the nanostructures, and their impacts on molecular mass transport dynamics.

Electrochemical sensing at nanoporous film‐coated electrodes

“…[ 88 ] However, current RNE‐based sensors often require sample pretreatment or electroactive marker addition, which prevents the use of RNE‐based sensors for in vivo biological studies. We currently explore the in‐depth fundamental understanding of chemical processes under nanoconfinement [ 53 ] to gain valuable insights into novel nanopore design and detection principles toward further improvement of sensor performance. Third, the in vivo application of RNE‐based sensors was recently demonstrated with carbon fiber microelectrodes coated with thin MPS films, [ 37 ] but further efforts are needed to incorporate RNE‐based sensors into compact devices for point‐of‐care diagnostics and for in vivo investigation of biological systems.…”

Single-Molecule Fluorescence Investigations of Solute Transport Dynamics in Nanostructured Membrane Separation Materials

“…13,24 SMT can offer both the trajectories of single molecules with positional precision beyond the diffraction limit and the speed of their motions at millisecond time resolution, 13,24,25 permitting the investigation of relationship between the structure and function of nanostructured materials. Furthermore, these techniques have been integrated with emission polarization and spectroscopic measurements for assessing the orientational dynamics of single molecules 12,13,36,37 and the polarity environments around single molecules, 37,38 respectively, in nanostructured materials. This Perspective will discuss recent single-molecule fluorescence studies on solute transport dynamics in nanostructured materials relevant to membrane separations, i.e., dense polymer films and nanoporous materials, with a focus on those published since 2020.…”

“…If the fluctuations are associated with solute passage across the detection volume, an autocorrelation function from the fluctuations provides the characteristic time scales of molecular transport processes and the average number of solute molecules involved in the fluctuations (fluorescence correlation spectroscopy, FCS). ,, The wide-field microscopic imaging is based on direct video recording of the motions of individual fluorescent molecules (single molecule tracking, SMT). , SMT can offer both the trajectories of single molecules with positional precision beyond the diffraction limit and the speed of their motions at millisecond time resolution, ,, permitting the investigation of relationship between the structure and function of nanostructured materials. Furthermore, these techniques have been integrated with emission polarization and spectroscopic measurements for assessing the orientational dynamics of single molecules ,,, and the polarity environments around single molecules, , respectively, in nanostructured materials.…”

Visualization of Electrochemically Accessible Sites in Flow-through Mode for Maximizing Available Active Area toward Superior Electrocatalytic Ammonia Oxidation

“…Most improvements in the electrochemical performance of flow-through electrodes (FTEs) have focused on the surface treatment and coating of commercially available porous electrodes . These electrodes are typically assessed using macroscopic properties that aggregate or average the behavior of a large number of microsurfaces located in different local microenvironments . Unfortunately, the complex pore structure of porous electrodes can significantly exacerbate the variability of these local microenvironments compared to planar electrodes, which further localizes the charge transfer process onto the electrochemically accessible portion of the overall interface .…”

“…13 These electrodes are typically assessed using macroscopic properties that aggregate or average the behavior of a large number of microsurfaces located in different local microenvironments. 17 Unfortunately, the complex pore structure of porous electrodes can significantly exacerbate the variability of these local microenvironments compared to planar electrodes, which further localizes the charge transfer process onto the electrochemically accessible portion of the overall interface. 18 It is essential to understand the spatial distribution of electrochemically accessible surface areas, which helps to guide the design and operation of the FTEs.…”