Abstract: The present invention encompasses membranous baculovirus-derived vesicle compositions having exposed on their external surfaces a ligator capable of selectively binding a ligand to be detected. The compositions also have exposed on their outer surfaces a signal reagent capable of reacting with another signal reagent to generate a signal capable of being detected. The present invention also encompasses assay methods for determining the presence and amount of a ligand in a sample using the membranous vesicle compositions of the present invention.