This chapter explores the transformative role of nanoparticles in medical diagnostics and imaging. Beginning with theranostic technologies that integrate therapeutic and diagnostic capabilities, it examines how multifunctional nanoplatforms are reshaping personalized medicine. The discussion delves into stimuli-responsive nanoparticle systems that react to specific biological triggers, enabling targeted drug delivery and real-time monitoring. Advances in cancer therapeutics using nanoparticles for enhanced detection and treatment are highlighted, alongside innovative biosensor devices that leverage nanomaterials for improved sensitivity and specificity in disease detection. The chapter also investigates cutting-edge imaging approaches that utilize nanoparticles to overcome the limitations of conventional techniques. Finally, it examines the integration of artificial intelligence and Internet of Things with nanodiagnostics, emphasizing how these convergent technologies are fostering intelligent, connected healthcare systems that enable earlier disease detection and more effective treatment strategies.