The present disclosure demonstrates that a nanovesicle comprising a membrane-associated lysosomal protein (saposin C “SapC”) incorporated into a phospholipid has a high fusogenic affinity for phosphatidylserine-rich domains on the surfaces of target cell membranes. It is believed that the nanovesicles target surface exposed phosphatidylserine on the membranes of cells associated with arthritis, allowing for detection of local tissue damage associated with arthritis. In plasma membranes, phosphatidylserine is normally present only on the inner leaflet but is “flipped” to the outer leaflet upon the presence of cell damage. Incorporation of the fluorophore in the nanovesicles allows for the in vivo visualization of the fluorophore in targeted tissue and provides a technique to detect and evaluate the onset and progression of arthritic disease in an animal. Furthermore, the use of the nanovesicle in optical imaging methods provides great promise for analyzing events occurring early in the pathogenesis of arthritis and arthritic disease.
