<p>Manufactured nanomaterials (MNMs) have transformed analytical and environmental applications by improving efficiency and reducing resource use. However, the "nano-paradox" has raised concerns about the use and development of nanotechnology, complicating regulatory agencies’ ability to monitor MNM’s environmental impact. In this work, a novel metric tool, the Nano Eco-Scale, is proposed to assess the greenness and environmental safety of nanomaterials used in analytical and environmental applications. The framework is based on the principles of green analytical chemistry and is aligned with REACH regulations for nanomaterials, while incorporating recommendations from the Organization for Economic Co-operation and Development for standardized characterization and safety evaluation. The tool assigns penalty points to deviations from the ideal nanomaterial across four main domains: synthesis conditions, nanomaterial toxicity, exposure during use, and waste generation and disposal. The overall score is calculated as 100 minus the total penalty points. The Nano Eco-Scale score supports the evaluation and comparison of environmental impacts associated with MNM-based analytical applications such as sensing, environmental monitoring, and water treatment. This approach encourages detailed characterization, highlights potential ecotoxicity risks, and promotes safer-by-design strategies. As a screening tool, it enables rapid comparisons and helps guide the selection of safer and more sustainable options. Additionally, it facilitates systematic data collection that could support future classification approaches. The developed tool supports regulatory efforts and advances the responsible use of nanotechnology in analytical and environmental fields.</p>