A polymer-coated cerium oxide based device and system is disclosed for detecting reactive oxygen species and monitoring chronic inflammation. The device and system encapsulate free therapeutic nanoparticle elements not present in a living body in a prosthetic or implantable unit. Embodiment one is a two-chamber structure with a reactive oxygen species (ROS) scavenging component on one end and at the opposite end is an imaging agent consisting of at least one of a fluorophore capable of fluorescence emission, a chemiluminescent agent, a magnetic relaxation agent and an X-ray contrast agent. Embodiment two is a single chamber device consisting of a multifunctional nanocomposite with a ROS-scavenging nanoparticle constituent (nanoceria) and a multimodal reporting nanoparticle component (i.e. Dex-IO-DiR). The device and system are utilized in treatment of diseases with a pro-inflammatory component, including, but not limited to, Crohn's disease, ulcerative colitis, inflammatory bowel disease, cystic fibrosis, arthritis, and cancer chemotherapy.