title: Feedback localization of freely diffusing fluorescent particles near the optical shot-noise limit.
abstract: 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 15 nm/sqrt Hz while collecting fewer than 5000 fluorescence photons/s. Fluorescent microspheres (diffusion coefficient 1.3 microm2/s) are tracked with a root-mean-square tracking error of 170 nm, within a factor of 2 of the theoretical limit set by photon counting shot noise.
authors.affiliation: Physical Measurement and Control 266-33, California Institute of Technology, Pasadena 91125, USA. berglund@caltech.edu
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Berglund
authors.forename: Kevin
authors.initials: K
authors.lastname: McHale
authors.forename: Hideo
authors.initials: H
authors.lastname: Mabuchi