In this work, we demonstrate the application of quantum dots (QDs) to several biologically relevant applications. QDs are synthesized by biological and organometallic routes and the relative merits of these methods are identified. Our results indicate that QDs can be functionalized and specifically targeted to both mammalian and bacterial cells. In the case of mammalian cells, they can be targeted to an engineered sodium channel for the purpose of sensing. In both mammalian and bacterial cells, the interaction with bioconjugated QDs can lead to phototoxicity due to the generation of reactive oxygen species (ROS).