Sub-Resolution Maximum-Likelihood Based Localization of Fluorescent Nanoparticles in Three Dimensions
François Aguet, BIG

Test Run • 03 April 2007 • BM 4.235

Abstract
Several recent studies have shown that fluorescent particles can be localized with an accuracy that is well beyond traditional resolution limits. Using a theoretical model of the image formation process that accounts for possible sources of noise, Cramer-Rao bounds have been used to define the theoretical limits. A crucial influence on these bounds is the mismatch of refractive indices that is usually present between immersion medium and specimen. This results in an axially shift-variant point spread function, meaning that the bounds change as a function of the particle's position in the z-direction. We investigate the theoretical bounds for this shift-variant model, and propose a maximum-likelihood estimator for the particle position in 3D (XYZ position). Using this estimator, sub-resolution localization at the nanometer scale is demonstrated on experimental data. The results provide optimal conditions for particle tracking and localization experiments.