Microscopy for recognition of individual biomolecules.

One frontier challenge in microscopy and analytical chemistry is the analysis of soft matter at the single molecule level with biological systems as most complex examples. Towards this goal we have developed two novel microscopy methods. Both employ highly specific molecular recognition schemes used by nature-the recognition of specific protein sites by antibodies and ligands. One method uses fluorescence labeled ligands for detecting single molecules in fluid systems like membranes (Fig. 1B). Unitary signals are reliably resolved even for millisecond illumination periods. The knowledge of the unitary signal from single molecules permits the determination of stoichiometries of component association (Fig. 3). Direct imaging of the diffusional path of single molecules became possible for the first time (Fig. 4). Using linear polarized excitation, the angular orientation of single molecules can be analyzed (single molecule linear dichroism, (Fig. 5), which opens a new perspective for detecting conformational changes of single biomolecules. In the other method, an antibody is flexibly linked to the tip of an atomic-force microscope. This permits the identification of receptors in multi-component systems. Molecular mapping of biosurfaces and the study of molecular dynamics in the ms to s range become possible with atomic force microscopy.