biostudies-literatureKrohn JHGerman Research Foundation3319-3328https://www.ebi.ac.uk/biostudies/studies/S-EPMC12709271biostudies-literatureUnknown124(20)In many quantitative investigations of biological systems, including, e.g., the study of biomolecular interactions, assembly and disassembly, aggregation, micelle and vesicle formation, or drug encapsulation, accurate determination of particle sizes is of key interest. Fluorescence correlation spectroscopy (FCS), with its exceptional sensitivity for molecular diffusion properties, has long been proposed as a valuable method to size small, freely diffusible particles with superior precision. It is conceptually related to the more widespread particle sizing technique dynamic light scattering (DLS) but offers greater selectivity and sensitivity due to the use of fluorescence rather than scattered light. However, in spite of these apparent advantages, FCS has never become established as a biopBiophysical journalFluorescence correlation spectroscopy for particle sizing: A notorious challenge.PMC12709271EXC-2094 \u2013 390783311Kaletta NQutbuddin YKrohn JHMamot ASchwille PfalseFluorescence correlation spectroscopy for particle sizing: A notorious challenge.In many quantitative investigations of biological systems, including, e.g., the study of biomolecular interactions, assembly and disassembly, aggregation, micelle and vesicle formation, or drug encapsulation, accurate determination of particle sizes is of key interest. Fluorescence correlation spectroscopy (FCS), with its exceptional sensitivity for molecular diffusion properties, has long been proposed as a valuable method to size small, freely diffusible particles with superior precision. It is conceptually related to the more widespread particle sizing technique dynamic light scattering (DLS) but offers greater selectivity and sensitivity due to the use of fluorescence rather than scattered light. However, in spite of these apparent advantages, FCS has never become established as a biop2025-01-01T00:00:00Z2025 Oct2026-06-06T04:17:51.494Z2026-05-25T03:11:56.399ZS-EPMC127092714013421610.1016/j.bpj.2025.03.017