Single-Molecule Investigations of Morphology and Mass Transport Dynamics in Nanostructured Materials

Abstract

Nanostructured materials such as mesoporous metal oxides and phase-separated block copolymers form the basis for new monolith, membrane, and thin film technologies having applications in energy storage, chemical catalysis, and separations. Mass transport plays an integral role in governing the application-specific performance characteristics of many such materials. The majority of methods employed in their characterization provide only ensemble data, often masking the nanoscale, molecular-level details of materials morphology and mass transport. Single-molecule fluorescence methods offer direct routes to probing these characteristics on a single-molecule/single-nanostructure basis. This article provides a review of single-molecule studies focused on measurements of anisotropic diffusion, adsorption, partitioning, and confinement in nanostructured materials. Experimental methods covered include confocal and wide-field fluorescence microscopy. The results obtained promise to deepen our understanding of mass transport mechanisms in nanostructures, thus aiding in the realization of advanced materials systems.

Diffusion of single dye molecules in hydrated TiO2 mesoporous films

“…On the other hand, advanced fluorescence microscopy methods including single molecule tracking (c) and fluorescence correlation spectroscopy (FCS) provide analytical tools to obtain quantitative information on the diffusion of single fluorescent tracer dyes inside porous materials 21 . These methods promise a more complete in-depth understanding of mass transport in these materials as illustrated in several works from the groups of Higgins [22][23][24][25][26] and Bräuchle [27][28][29] .…”

Single‐Molecule and Ensemble Diffusivities in Individual Nanopores with Spatially Dependent Mobility

“…[14] Although generally accepted, the experimental validation of ergodicity is scarce. It was only recently that Feil et al [15] reported on the validity of the ergodic theorem fort he first time by comparing single-molecule diffusivities in ap orous sodium borosilicate monolith,o btained by using single-molecule tracking, [16][17][18][19] with ensemble diffusivities which were based on pulsed field-gradient nuclear magnetic resonance. [20,21] The found single-molecule and ensemble diffusivities were in good agreement despite an order of magnitude differencei nt he concentrations that had to be used in these different experimentala pproaches.…”

Electron Hopping through Redox Moieties Anchored to Well‐Defined Nanostructures

“…[1][2][3] Recent progress in controlled nanostructure fabrication and highly sensitive measurement techniques enables us to explore molecular-level understanding of fundamental transport processes. We employ monolithic materials comprising aligned cylindrical nanoscale pores/domains as model systems, and measure mass/charge-transport phenomena within these materials using single-molecule fluorescence and electrochemical techniques.…”

“…Note that this Commentary does not describe our mass-transport studies using single-molecule fluorescence techniques, which are based on close collaboration with Prof. Daniel Higgins (Kansas State University) and were discussed in our recent perspective and review articles. [2,3] My interest in nanostructured materials was initiated while I was a postdoc with Prof. Richard Crooks at Texas A&M University (2001)(2002)(2003)(2004). During this time, I studied resistivepulse detection with a carbon nanotube pore for characterization of individual nanoparticles [6][7][8] and electrokinetic enrichment of DNA with a track-etched nanoporous membrane incorporated into a microfluidic device.…”

“…My research group currently focuses on investigating mass and charge transport within nanostructured materials to gain design principles of highly efficient separation and sensing media . Recent progress in controlled nanostructure fabrication and highly sensitive measurement techniques enables us to explore molecular‐level understanding of fundamental transport processes.…”