FRET-sensing of multivalent protein binding at the interface of targeted biomimetic microparticles functionalized with tunable fluorescent lipids

Cell adhesion is a fundamental phenomenon for cell communication and regulation. Adhesion sites are triggered by the binding of single ligand-receptor pairs that will initiate the formation of clusters of receptors. To study cell adhesion in live cells with microscopy techniques, there is a need of fluorescent particles targeted towards membrane receptors with a signal sensitive to the binding and movement of receptors and ligands at the interface. We propose new biomimetic fluorescent lipid microparticles for membrane receptor targeting and sensing. The particles are functionalized with tailor-made fluorescent lipids targeted towards lectins or biotin membrane receptor and can be specifically recognized and internalized by cells as evidenced by their phagocytosis in primary murine bone-marrow derived macrophages. By using a FRET pair of fluorescent mannolipids, it was possible to detect the presence of concanavalin A in solution by energy transfer showing that the particles can sense receptor binding at the interface and the associated movement of the ligands at the site of adhesion. Our results demonstrate that this biosensing platform can be specifically internalized by phagocytes, effectively mimicking a bacteria, and reveal short-range interactions of surface receptors via FRET.