Nanotechnology-based sensors have emerged as a cutting-edge solution for real-time pollution detection, offering unprecedented sensitivity, selectivity, and speed in monitoring environmental contaminants. Leveraging the unique physicochemical properties of nanomaterials—such as high surface-to-volume ratios, tunable surface chemistry, and enhanced catalytic activity—these sensors can detect pollutants at extremely low concentrations, often at the parts-per-billion or even parts-per-trillion level. Applications span across air, water, and soil quality monitoring, enabling the detection of heavy metals, volatile organic compounds (VOCs), greenhouse gases, particulate matter, and biological contaminants. Real-time sensing capabilities allow for immediate identification of pollution sources, supporting rapid decision-making in environmental management, public health interventions, and regulatory enforcement. Common designs include carbon nanotube-based chemiresistors, metal oxide nanostructure gas sensors, quantum dot fluorescence sensors, and surface plasmon resonance (SPR) devices. Integration with wireless communication, Internet of Things (IoT) platforms, and mobile applications further enhances data accessibility and enables large-scale, distributed environmental monitoring networks. Despite their promise, nanotech sensors face challenges related to fabrication costs, long-term stability, sensor fouling, and standardization for regulatory compliance. Continued advancements in material engineering, nanofabrication techniques, and energy-efficient electronics are expected to improve their robustness and affordability. Future directions include the development of self-powered, biodegradable, and multifunctional nanosensors capable of simultaneous detection of multiple pollutants. By enabling accurate, real-time environmental data collection, nanotech sensors have the potential to transform pollution monitoring from a periodic, labor-intensive task into a continuous, proactive process, ultimately contributing to cleaner ecosystems and healthier communities.