Emerging nanosensor technologies for the rapid detection of heavy metal contaminants in agricultural soils.

The accumulation of heavy metals in agricultural soils presents a growing threat to food safety and human health. Conventional laboratory-based methods for heavy metal detection, while highly sensitive, are impractical for widespread, real-time soil monitoring due to their cost, complexity, and lack of portability. In response, nanosensor technologies have emerged as promising alternatives, offering rapid, sensitive, and field-deployable detection platforms. This review critically examines the current landscape of electrochemical and optical nanosensors engineered for trace metal analysis in soil environments. Electrochemical platforms, particularly those employing nanomaterial-modified screen-printed electrodes and anodic stripping voltammetry, demonstrate excellent sensitivity and portability, though challenges remain in achieving selectivity and mitigating matrix interference. Optical nanosensors, including colorimetric, fluorescent, and surface-enhanced Raman scattering (SERS)-based systems, offer diverse mechanisms of detection and ultralow detection limits but are often limited by soil turbidity, biofouling, and substrate instability. Particular attention is given to the integration of advanced materials such as metal-organic frameworks, carbon-based nanomaterials, and "green" quantum dots, which aim to improve sensor performance and environmental safety. The review also explores the convergence of nanosensor deployment with data science, emphasizing the role of machine learning in signal deconvolution, calibration, and real-time decision support. Finally, the article highlights future directions, including the development of anti-fouling coatings, sustainable fabrication methods, multiplexed detection arrays, and sensor networks integrated via the Internet of Things. Together, these advances suggest a pathway toward robust, intelligent, and scalable soil monitoring systems critical for precision agriculture and environmental stewardship.