7-Nitrobenzo-2-oxa-1,3-diazole (NBD) Fluorophore-Based Sensors for Hg(II) Detection: A Concise Review and Future Development Strategies

Hg(II) ions pose a significant environmental threat due to their conversion into methylmercury, a highly neurotoxic compound that bioaccumulates in the food chain. Conventional detection methods like atomic absorption spectroscopy and inductively coupled plasma mass spectrometry offer high sensitivity but are limited by cost, complexity, and operational requirements. Fluorescence-based sensors have emerged as promising alternatives, offering rapid, sensitive, and selective Hg(II) detection suitable for real-time and field applications. Among various fluorophores, 7-nitrobenzo-2-oxa-1,3-diazolyl (NBD) stands out for its excellent photophysical properties and versatile sensing mechanisms involving internal charge transfer (ICT) and photoinduced electron transfer (PET). Recent developments have explored NBD-based probes employing diverse detection modes and conjugated platforms to enhance performance. This review highlights these advances, sensing strategies, challenges, and future directions for designing efficient Hg(II) fluorescent sensors.