The chapter delves into the burgeoning field of nanosensors and their transformative impact on disease diagnostics. Nanosensors, leveraging the unique properties of nanomaterials, offer unprecedented sensitivity and specificity in detecting biomarkers associated with various diseases. This chapter outlines the fundamental principles behind nanosensor technology, including the synthesis and functionalization of nanomaterials, as well as the mechanisms through which they interact with biological molecules. A comprehensive overview of different types of nanosensors, such as optical, electrochemical, and magnetic nanosensors, is provided, highlighting their respective advantages and limitations. The application of nanosensors in diagnosing a range of diseases, from infectious diseases and cancer to neurological and cardiovascular disorders, is thoroughly examined through case studies and recent advancements. Furthermore, the chapter addresses the challenges facing the clinical translation of nanosensors, including issues related to biocompatibility, reproducibility, and regulatory approval. Future perspectives on the integration of nanosensors with other diagnostic technologies and their potential role in personalized medicine and point-of-care testing are also discussed. Through this detailed exploration, the chapter aims to underscore the pivotal role of nanosensors in advancing disease diagnostics and shaping the future of healthcare.