Nanobiotechnology has emerged as a promising field with diverse applications in the agriculture sector and it has significantly aided in plant disease diagnosis and management. Amongst the nanotechnology-based methods, nanosensors have quickly become essential tools to diagnose and treat plant diseases. Nanosensors have enhanced agricultural output by boosting crop yield. By influencing the targeted treatment, nanosensors have revolutionized phytodiagnostics with extreme sensitivity, rapid results and precise identification. Nanosensors can be employed to monitor soil quality and detect the presence of plant pathogens such as viruses, bacteria and fungi including their physiological indicators enabling early disease prognosis. These indicators often involve changes in the plant’s metabolism, physiology, or biochemistry in response to infection. Early screening of pathogens prevents the spread of disease as well as safeguards leading to reduced economic losses. Accurate evaluation leads to effective treatments of crop diseases and helps to cut down the misuse of pesticides. Precise diagnosis ensures that the right pesticide is used at the right time and dosage, minimizing the risk of resistance. Optical, electrochemical, mechanical, transducable and resistive properties of nanosensors have led to the development of a large variety of these sensors which provides precision diagnostics and early intervention. This chapter hints on brief introduction of nanosensors, the mechanism on which they work and how they are classified according to their specific properties. Additionally, their applications have also been briefly explained. Moreover, some of the proposed drawbacks are appended to catch the attention of future research. Subsequently, the future prospects about transformation of plant disease diagnosis into new horizons of early plant disease detection for sustainable agriculture are also presented.