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Published January 15, 2007 | public
Journal Article Open

Feedback localization of freely diffusing fluorescent particles near the optical shot-noise limit


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 μm^2/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.

Additional Information

© 2006 Optical Society of America. Received August 7, 2006; revised October 10, 2006; accepted October 12, 2006; posted October 18, 2006 (Doc. ID 73852); published December 23, 2006 K. McHale acknowledges support from an NDSEG fellowship. This work was supported by NSF grant CCF-0323542 and by the Institute for Collaborative Biotechnologies through grant DAAD19-03-D-0004 from the Army Research Office. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors, and do not necessarily reflect the views of either funding agency.


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