Visualizing single-molecule diffusion in mesoporous materials

• Published in: Nature 2007-11, Vol.450 (7170), p.705-708
• Main Authors: Zürner, Andreas, Kirstein, Johanna, Döblinger, Markus, Bräuchle, Christoph, Bein, Thomas
• Format: Article
• Language: English
• Subjects: Catalysis; Chemistry; Colloidal state and disperse state; Diffusion; Dynamical systems; Dynamics; Electron microscopy; Exact sciences and technology; Fluorescence; General and physical chemistry; Humanities and Social Sciences; letter; Light microscopy; Materials science; Molecular structure; multidisciplinary; Nanostructure; Optical microscopy; Porosity; Porous materials; Science; Surfactants; Transmission electron microscopy
• ISSN: 0028-0836; 1476-4687; 1476-4679
• DOI: 10.1038/nature06398

Guest appearance Materials with mesoscale pores (that is, with diameters of several hundred nanometres) have many potential applications — including storage, separation and catalytic conversion — most of which depend on the diffusion of 'guest' molecules through the pores. Yet no method existed to correlate the guests' motion with the structure of the material. This looks set to change with the development of a technique combining electron microscopy with optical single-molecule tracking to visualize molecular diffusion in a mesoporous material. For the first time, guest molecules (dyes in this case) can be 'seen' changing speed or direction in response to structural features of the host on a nanometre scale. This opens the way to a deeper understanding of the properties of mesoporous solids. Electron microscopy is combined with optical single-molecule tracking to visualize molecular diffusion in a nanoporous material. For the first time, guest molecules can be 'seen' changing speed or direction in response to structural features of the host. Periodic mesoporous materials formed through the cooperative self-assembly of surfactants and framework building blocks can assume a variety of structures 1 , 2 , 3 , and their widely tuneable properties make them attractive hosts for numerous applications 4 , 5 , 6 , 7 . Because the molecular movement in the pore system is the most important and defining characteristic of porous materials 8 , it is of interest to learn about this behaviour as a function of local structure. Generally, individual fluorescent dye molecules can be used as molecular beacons with which to explore the structure of—and the dynamics within—these porous hosts 9 , 10 , 11 , 12 , 13 , and single-molecule fluorescence techniques provide detailed insights into the dynamics of various processes, ranging from biology 14 , 15 to heterogeneous catalysis 16 . However, optical microscopy methods cannot directly image the mesoporous structure of the host system accommodating the diffusing molecules, whereas transmission electron microscopy provides detailed images of the porous structure 17 , but no dynamic information. It has therefore not been possible to ‘see’ how molecules diffuse in a real nanoscale pore structure. Here we present a combination of electron microscopic mapping and optical single-molecule tracking experiments to reveal how a single luminescent dye molecule travels through linear or strongly curved sections of a mesoporous channel syst