In 2024, Steffen J. Sahl and colleagues measured intramolecular spacing as small as 1 nm (as low as 1 Å in planar projection) using MINFLUX fluorescence microscopy (Sahl
et al. 2024). Previously, Förster resonance energy transfer (FRET) had been utilized for measuring molecular distances and structures in fluorescence microscopy since the 1960s, but the FRET technique is highly nonlinear. The MINFLUX technique uses a "donut" shaped light for excitation (
Fig. 1A). The closer the fluorescent molecule is to the center of the ring, the weaker the fluorescence intensity emitted, and the position with the smallest number of photons found through the fit is the precise location of the fluorescent molecule (Balzarotti
et al. 2017). This study shows that MINFLUX localization determines (internal) molecular distances linearly with sub-nanometer precision at room temperature. In the study, they selected poly-proline chains (poly-proline chain, P-5 to P-40) of different lengths as samples and attached the small molecule fluorescent dye DiMeO-ONB-SiR637 to the ends of the poly-proline chains, and the measurements demonstrated the distribution of the distances of the poly-proline, validating the MINFLUX technology as a "linear measuring scale" (
Fig. 1B). Meanwhile, their results also revealed that specific conformations of the dimerization of the PAS domain of histidine kinase, including parallel and antiparallel arrangements, show great potential in cells. Their work shows that fluorescence microscopy is undergoing a seminal shift from merely resolving spatial distributions to precise localization, enabling direct revelation of the biomolecule structure and function with minimal invasiveness.