A method to estimate the effective point spread function of static single molecule localization microscopy images

Single molecule localization microscopy (SMLM) permits the visualization of cellular structures an order of magnitude smaller than the diffraction limit of visible light, and an accurate, objective evaluation of the resolution of an SMLM dataset is an essential aspect of the image processing and analysis pipeline. Here we present a simple method that uses the pair autocorrelation function evaluated both in space and time to measure the time-interval dependent effective point spread function of SMLM images of static samples. Using this approach, we demonstrate that experimentally obtained images typically have effective point spread functions that are broader than expected from the localization precision alone, due to additional uncertainty arising from factors such as drift and drift correction algorithms. The method is demonstrated on simulated localizations, DNA origami rulers, and cellular structures labelled by dye-conjugated antibodies, DNA-PAINT, or fluorescent fusion proteins. STATEMENT OF SIGNIFICANCESingle molecule localization microscopy (SMLM) is a class of imaging methods that resolve fluorescently labeled structures beyond the optical resolution limit of visible light. SMLM detects stochastically blinking labels over time, and localizes each blink with precision of order 10 nm. The effective resolution depends on factors such as signal-to-noise ratio, localization algorithm, and several post-processing steps such as stage drift correction. We present a method to evaluate this effective resolution by taking advantage of temporal correlations of fluorophore blinking to separate the distribution of pairs of localizations from the same molecule from those from different molecules. The method is robust on useful timescales for a range of SMLM probes.