We report near-optimal tracking of freely diffusing fluorescent particles in a quasi-two-dimensional geometry via photon counting and real-time feedback. We present a quantitative statistical model of our feedback network and find excellent agreement with the experiment. We monitor the motion of a single fluorescent particle with a sensitivity of while collecting fewer than . Fluorescent microspheres (diffusion coefficient ) are tracked with a root-mean-square tracking error of , within a factor of 2 of the theoretical limit set by photon counting shot noise.
© 2006 Optical Society of AmericaFull Article | PDF Article