Fundamental precision limits of fluorescence microscopy: a new perspective on MINFLUX

TL;DR

This paper introduces a comprehensive multi-parameter estimation framework for fluorescence microscopy, revealing that emitter brightness significantly influences localization precision and providing a more accurate assessment of super-resolution techniques like MINFLUX.

Contribution

The authors develop a novel multi-parameter estimation framework that accounts for unknown parameters such as brightness, improving the accuracy of localization precision assessment in fluorescence microscopy.

Findings

Localization precision improves mainly with increased brightness.

Decreasing beam separation offers limited benefits for precision.

The framework applies broadly to various OFM methods, including MINFLUX and STED.

Abstract

In the past years, optical fluorescence microscopy (OFM) made steady progress towards increasing the localisation precision of fluorescent emitters in biological samples. The high precision achieved by these techniques has prompted new claims, whose rigorous validation is an outstanding problem. For this purpose, local estimation theory (LET) has emerged as the most used mathematical tool. We establish a novel multi-parameter estimation framework that captures the full complexity of single-emitter localisation in an OFM experiment. Our framework relies on the fact that there are other unknown parameters alongside the emitter's coordinates, such as the average number of photons emitted (brightness), that are correlated to the emitter position, and affect the localisation precision. The increasing complexity of a multi-parameter approach allows for a more accountable assessment of the precision. We showcase our method with MINFLUX microscopy, the OFM approach that nowadays generates images with the best resolution. Introducing the brightness as an unknown parameter, we shed light on features that remain obscure in the conventional approach: the precision can be increased only by increasing the brightness, (i.e., illumination power or exposition time), whereas decreasing the beam separation offers limited advantages. We demonstrate that the proposed framework is a solid and general method for the quantification of single-emitter localisation precision for any OFM approach on equal footing, evaluating the localization precision of stimulated emission depletion (STED) microscopy and making a comparison with MINFLUX microscopy.