DSPE-PEG(2000)-Amine is coated on the surface of the fluorescein diacetate (FDA) nanocrystals to provide a interface for the antibody coupling. The FDA[DSPE-PEG(2000)Amine]-modified biolabels have a highly stable colloidal suspension with minimized nonspecific interactions. The adsorbed DSPE-PEG(2000)Amine layer causes the FDA nanocrystals to disperse in water and prevents their aggregation, hence conferring colloidal stability.