The investigation of molecules as individuals has grown rapidly in recent years, and in the process has uncovered molecular properties not normally accessible by ensemble experiments. In particular, the direct characterization of biologically important molecules such as enzymes, molecular motors, or receptors and entire signaling complexes in action, for example in a live biological cell, yielded un- pected insights. Common approaches for studying single molecules include the electrical detection of ion channels in membranes, the measurement of the dynamics of (bio)chemical reactions between individual molecules, the imaging of individual molecules by scanning probe techniques or by fluorescence correlation spectr- copy, and the direct monitoring of single molecules by optical microscopies, to mention a few. The application of these techniques in physics, chemistry, and bi- ogy has opened new areas of nanotechnology. This book provides a representative selection of recent developments in the rapidly evolving field of single molecule techniques of importance in life sciences and will have future impact on the quan- tative description of biological processes. The editors of this book hope that the chapters, written by leading scientists in the field, will attract students and scientists from different disciplines, provide them with an authentic insight into this young field of research, allow them to evaluate experimental methods and results, and thereby give them support for their own research. Lausanne Rudolf Rigler September 2007 Horst Vogel v Contents 1 Nanophotonics and Single Molecules. . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 W. E. Moerner, P. James Schuck, David P.