Metal nanoparticles (MNPs) typically range in size from 1 to 100 nm, and their unique physical and chemical properties make them extremely useful in a number of applications, including disease detection. This chapter explores the essential aspects of MNPs, covering synthesis techniques and characterization methods, while emphasizing their properties, such as localized surface plasmon resonance, a high surface-to-volume ratio, as well as ferromagnetism and superparamagnetism. MNPs enhance optical, colorimetric, electrochemical sensing, and imaging contrast. Furthermore, the capability of MNPs to improve diagnostic sensitivity and precision has been demonstrated by their recent integration into advanced imaging modalities, as well as rapid and point-of-care testing, including microfluidics, lab-on-a-chip devices, and biosensor devices. Additionally, several studies demonstrated the successful application of MNPs in diagnostic settings, although issues with stability, toxicity, and regulatory barriers remain to be addressed. By addressing these trends and obstacles, this chapter aims to provide a perspective on the transformational role of MNPs in medical diagnostics and their potential to address major problems in existing diagnostic procedures.