Engineered nanoparticles are found in many everyday products and hold great potential as therapeutic agents. Accordingly, it is critical to consider how engineered nanoparticles interact with physiological and ecological systems. This work focuses on functional assessment of bacterial cell behavior following exposure to Au, nanodiamond, and semiconductor nanoparticles. Functional considerations include biofilm formation, cell delivery of chemical messengers, production of reactive oxygen species, and gene expression, among others. In this new collaborative study, obtained bacterial toxicity results can be compared to those o btained in other model systems (lipid bilayers and the multicellular water flea, Daphnia) to identify common modes of nanoparticle interactions and the resultant effects. The goal of this work is to discover critical nanoparticle features that determine cellular toxicity and then redesign nanoparticles to promote sustainable use.