Exploration of nanostructured channel systems with single-molecule probes

Abstract

Molecular movement in confined spaces is of broad scientific and technological importance in areas ranging from molecular sieving and membrane separation to active transport through ion channels. Whereas measurements of ensemble diffusion provide information about the overall behaviour of the guest in a porous host, tracking individual molecules provides insight into both the heterogeneity and the mechanistic details of molecular diffusion as well as into the structure of the host. Here, we show how single dye molecules can be used as nanoscale probes to map out the structure of mesoporous silica channel systems prepared as thin films via cooperative self-assembly of surfactant molecules with polymerizable silicate species. The dye molecules act as beacons while they diffuse through the different structural phases of the host: the structure of the trajectories, the diffusivities and the orientation of single molecules are distinctive for molecules travelling in the lamellar and the hexagonal mesophases. These experiments reveal unprecedented details of the host structure, its domains and the accessibility as well as the connectivity of the channel system.

Review. Fluorescence Microscopy Studies of Porous Silica Materials

“…While measurements of ensemble diffusion of molecules in porous hosts provide information about the overall behavior of the guest in the host, tracking of individual molecules provides insights into the heterogeneity and the mechanistic details of molecular diffusion as well as the structure of the host. In our SMM experiments we have shown how single dye molecules can be used as nanoscale probes to map out the structure of mesoporous silica channel systems prepared as thin films via the cooperative selfassembly of surfactant molecules with polymerizable silicate species [52,53]. The dye molecules act as beacons while they diffuse through the different structural phases of the host: the structure of the trajectories, the diffusivities and the orientation of single molecules are distinctive for molecules traveling in the lamellar and the hexagonal mesophases [54].…”

“…This trajectory gives detailed information about the pathway of the molecule within the pores and thus the structure of the host. Such movies can be found in the Supplementary Material of articles by Kirstein et al [53] or Zürner et al [52].…”

A Man for Single Molecules

“…This elegant method allows one to visualize the molecular dynamics in and the structural details of pore systems with pore sizes at the nanometer scale including the formation of domains, accessibility of the channels and connectivity of the network. [11,12] On the occasion of Christoph Bräuchle's 65th birthday, we dedicate this issue of ChemPhysChem to his honor and to the exemplary research he has performed. In this issue, several authors from different countries have contributed groundbreaking research articles, giving an overview of the current status of single-molecule research.…”

The complexity of mesoporous silica nanomaterials unravelled by single molecule microscopy

“…3) is typically 6.1 (AE0.1) nm and for the hexagonal phase it is 6.3 (AE0.1) nm according to X-ray diffractometry patterns. 53 These are just average values. The recorded peaks show a distinct broadness, which indicates that a distribution of pore-to-pore distances and thus pore sizes is present in the samples.…”