Chemically stable nanoparticles having precisely controlled compositions, sizes, shapes, and surface functionalization will be employed to investigate how they interact with lipid bilayers and with model organisms, toward the goal of understanding the factors influencing the routes by which nanoparticles enter biological systems. Experiments will use lipid bilayers as model systems for biological membranes, Shewanella oneidensis as a single-cell model, and Daphnia magna as a model whole organism. The resulting molecular level changes in gene expression and metabolism will be characterized and used as biomarkers to evaluate biological responses induced by different nanoparticles and surface functionalization. These biological responses will in turn be used to inform the design and synthesis of nanoparticles having reduced adverse biological impacts. State-of-the-art analytical approaches, including nonlinear optical spectroscopies and genome sequencing tools, will be developed and used to characterize the interaction of functionalized nanoparticles with cells and simple organisms at the molecular level. These results will be informed by concurrent computational studies to provide fundamental insights into nanoparticle-biological interactions and to develop models with which to evaluate future nanomaterials.