Nitric oxide (NO), a diatomic free radical, regulates multiple physiological functions in the cardiovascular, respiratory, immune, and nervous systems. The complex and wide ranging roles of NO in normal physiology thus demands methods for generating NO in a controlled manner. As such, much research has focused on the synthesis of NO donors to allow controlled NO release. We have recently developed several classes of nanoparticles capable of storing and releasing NO at different rates dependent on the nanoparticle composition. Indeed, the advantage of NO-releasing nanoparticles over conventional NO donor systems is the ability to store large concentrations of NO on a single molecular scaffold. In addition to the unprecedented NO payload, the size and exterior of the nanoparticle are easily modified to confer specific functionality for imaging, targeting, and/or enhanced cellular uptake. This presentation will focus on the synthesis and characterization of silica nanoparticles, and their cytotoxicity on human ovarian epithelial normal and cancer cell lines.