Tracking of fluorescent molecules diffusing within membranes

A new method is proposed for tracking fluorescing single molecules diffusin g within a two-dimensional membrane. It is based on a confocal microscopy s etup with a constantly rotating laser focus, which follows the position of the molecule. The optimization and efficiency of the method are theoretical ly studied for a broad range of experimentally realistic conditions. The pr oposed method allows for a long-time observation of diffusing molecules whi le allowing the application of fast spectroscopic techniques such as fluore scence decay time determination or fluorescence anisotropy measurements.