We investigated the biological activity of Au nanoparticles with a mean diameter of 30 nm which were capped with scopoletin, a natural coumarin isolated from Artemisia roxburghiana along with eleven other natural products. The NO inhibitory activity of scopoletin was unaffected by conjugation to the Au nanoparticles. A luminol chemiluminescence assay showed instead that conjugation increased the prevention of an oxidative burst of reactive oxygen species (ROS) in whole blood phagocytes and isolated neutrophils (PMN) by about three times.