Three-dimensional fluorescence lifetime imaging of a molecular rotor at complex interfaces of grease
Year: 2026
Type: preprint
Abstract: Fluorescence lifetime imaging microscopy (FLIM) maps local physicochemical properties with a confocal laser-scanning microscope. Soft materials are promising targets for FLIM because they demand multi-scale microanalysis; of particular interest are the interfacial properties of complex fluids. However, within each pixel, interfacial and non-interfacial FLIM signals are mixed, which complicates the physical interpretation of FLIM results at interfaces. Here, we propose a systematic FLIM approach: acquire three-dimensional FLIM data at near-diffraction-limited resolution, identify the mixing mechanism by phasor analysis, and perform pixel-level mono- or bi-exponential fitting according to that mechanism. As a proof of concept, we apply this approach to the complex interfaces of grease, in which tens-of-nanometer-scale thickener fibers form a three-dimensional network in the base oil. We prepare a grease labeled with a molecular-rotor dye whose fluorescence lifetime is coupled to the oil viscosity. Three-dimensional FLIM reveals that the lifetime significantly increases at the fiber–oil interfaces. Phasor analysis shows that this lifetime heterogeneity originates from a binary mixture of free-oil and fiber-bound states. Pixel-level bi-exponential fitting then separates the FLIM images into two state maps. In the fiber-bound state, the intramolecular rotation of the dye is arrested, indicating that the oil is solid-like rather than viscous at the interfaces. Beyond the ~180 nm resolution of our images, the lifetime-domain separation resolves the coexistence of the two states within a single diffraction-limited voxel. Finally, we generalize our approach so that FLIM can be broadly applied to map interfacial properties in soft complex materials.
Source: ChemRxiv
Institutions: Kyodo Yushi Co., Ltd. (Japan), Tohoku University
Language: English
Subfield: Biophysics
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W7214682354