We determined the effect of aggregation and coating thickness of gold on the luminescence of nanoparticles engulfed by macrophages and in gelatin phantoms. Thin gold-coated iron oxide nanoclusters (nanoroses) have been developed to target macrophages to provide contrast enhancement for near-infrared optical imaging applications. We compare the brightness of nanoroses luminescent emissions in response to 635 nm laser excitation to other nanoparticles including nanoshells, nanorods, and Cy5 conjugated iron oxide nanoparticles. Luminescent properties of all these nanoparticles were investigated in monomeric and aggregated form in gelatin phantoms and primary macrophage cell cultures using confocal microscopy. Aggregation of the gold nanoparticles increased luminescence emission and correlated with increased surface mass of gold per nanoparticle (nanoshells brightness with wt of gold (g)/nanoparticle versus original nanorose with wt of gold/nanoparticle, ). Nanoshells showed greater luminescent intensity than original nanoroses or Cy5 conjugated iron oxide nanoparticles when compared as nanoparticles per macrophage ( versus versus , , respectively, ANOVA), but showed relatively poor macrophage uptake ( versus versus , , student -test nanoshells versus nanoroses). Enhancement of gold fluorescent emissions by nanoparticles can be achieved by reducing the thickness of the gold coating, by clustering the gold on the surface of the nanoparticles (nanoshells), and by clustering the gold nanoparticles themselves.