Localization of a fluorescent source without numerical fitting.

We present an algebraic solution to the problem of localizing a single fluorescent particle with sub-diffraction-limit accuracy. The algorithm is derived and its performance studied experimentally. Isolated 20 nm fluorescent beads were imaged using a wide-field microscope at two different positions separated by 100 nm and at a range of signal-to-noise ratios (SNR). The data were analyzed using both the new algorithm and the standard approach of fitting the data to a Gaussian profile. Results indicate that the proposed approach is nearly as accurate as Gaussian fitting across a wide range of SNR while executing over 200 times faster. In addition, the new algorithm is able to localize at lower SNR than the fitting method.