3-D tracking of fluorescent nanoparticles in a confocal microscope

A system for tracking fluorescent particles in three dimensions based on a standard confocal microscope is described. The method scans the detection volume of the microscope through a six-point measurement pattern, estimates the position of the particle from the measurements, and uses a linear optimal controller to regulate the distance between the center of the measurement pattern and the position of the particle. Experimental results on tracking freely diffusing quantum dots are presented and show good agreement to estimates calculated from CCD images captured during the tracking process.