Membrane Architecture‐Dependent Photophysics of Conjugated Oligoelectrolytes Distinguishes Extracellular Vesicles From Lipoproteins

ABSTRACT Lipid‐bound nanoparticles (LBNs), including extracellular vesicles and lipoproteins, are characterized by distinct membrane architectures that modulate biological functions. However, optical probes capable of directly distinguishing lipid bilayers from monolayers remain limited. Here, we establish conjugated oligoelectrolytes (COEs) as molecular transducers of lipid membrane architecture capable of converting differences in supramolecular organization into distinct optical signatures. Using model systems, we show that COEs intercalate across lipid bilayers but preferentially adsorb onto lipid monolayers. Employing COE‐KP, a probe sensitive to water contact, enabled direct interrogation of membrane microenvironments. Fluorescence lifetime imaging microscopy (FLIM) revealed that COE‐KP exhibits shorter fluorescence lifetimes when associated with lipid monolayers relative to bilayers. Atomistic molecular dynamics simulations corroborate these observations by revealing distinct insertion energetics at monolayer and bilayer interfaces. Guided by this mechanistic framework, we applied COEs in nano‐flow cytometry to discriminate red blood cell‐derived extracellular vesicles from very‐low‐density lipoproteins. These results demonstrate that COEs adopt distinct binding orientations depending on lipid organization and highlight their utility as optical probes for analyzing LBNs. Beyond enabling analysis of biologically relevant LBNs, this work establishes a general molecular framework linking membrane architecture to probe orientation and photophysics, providing a strategy for designing optical reporters that decode membrane organization.