No abstract

We have developed a method that combines dynamic force microscopy with the simultaneous molecular recognition of an antigen by an antibody, during imaging. A magnetically oscillated atomic force microscopy tip carrying a tethered antibody was scanned over a surface to which lysozyme was bound. By oscillating the probe at an amplitude of only a few nanometers, the antibody was kept in close proximity to the surface, allowing fast and efficient antigen recognition and gentle interaction between tip and sample. Antigenic sites were evident from reduction of the oscillation amplitude, as a result of antibody-antigen recognition during the lateral scan. Lysozyme molecules bound to the surface were recognized by the antibody on the scanning tip with a few nanometers lateral resolution. In principle, any ligand can be tethered to the tip; thus, this technique could potentially be used for nanometer-scale epitope mapping of biomolecules and localizing receptor sites during biological processes.

In this review, we report recent molecular recognition studies of our group. The surface chemistry by which ligands are covalently coupled to force microscopy tips is described. Poly(ethylene glycol), which is used as spacer for the ligands, was shown to be a most suitable crosslinker for force spectroscopy and microscopy experiments. Basic principles of force spectroscopy are discussed and the successful application of this technique to several biological systems is demonstrated. Information about kinetic rates, affinities, and the dynamic structure of the binding pocket are obtained. Furthermore, it is shown that combining molecular recognition with dynamic force microscopy leads to recognition imaging and renders localization of binding sites with nm accuracy possible. These techniques show great potential for investigating the molecular dynamics of ligand-receptor binding and the epitope mapping of recptors during biological processes.

The thermal stability of faceted self-assembled PbSe quantum dots during annealing is investigated. With increasing annealing time, the dot density is found to decrease rapidly with a simultaneous increase of the average island volumes. In addition, a shape transition from pyramidal islands to truncated pyramids is observed for islands exceeding a critical height of 160 Å. The evolution of island volumes and densities is consistent with Oswald ripening by interface-reaction-limited mass transfer. This is a clear indication that the as-grown islands do not represent an equilibrium structure and that their narrow size dispersion is a purely kinetic effect.