Two-photon MINFLUX with doubled localization precision

Abstract Achieving localization with molecular precision has been of great interest for extending fluorescence microscopy to nanoscopy. MINFLUX pioneers this transition through point spread function (PSF) engineering, yet its performance is primarily limited by the signal-to-background ratio. Here we demonstrate theoretically that two-photon MINFLUX (2p-MINFLUX) could double its localization precision through PSF engineering by nonlinear effect. Cramér-Rao Bound (CRB) is studied as the maximum localization precision, and CRB of two-photon MINFLUX is halved compared to single-photon MINFLUX (1p-MINFLUX) in all three dimensions. Meanwhile, in order to achieve same localization precision with 1p-MINFLUX, 2p-MINFLUX requires only 1/4 of fluorescence photons. Exploiting simultaneous two-photon excitation of multiple fluorophore species, 2p-MINFLUX may have the potential for registration-free nanoscopy and multicolor tracking.