Tracking of fluorescent molecules diffusing within membranes

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