Copper chlorophyll (CC), the hydrophobic pigment applied in food, is employed as a contrast agent instead of Au nanoparticles (NPs) to label polymeric NPs for in vivo observation by electron microscopy. Using the nanoprecipitation method without surfactants CC is aggregated in coordinately saturated form and synchronously encapsulated in the matrix of polymeric NPs without other complex pretreatments, which may ensure the stability of CC in NPs.