Fluorescence-based sensors for environmental monitoring of small hazardous molecules: Recent trends and future prospects

Fluorescence-based sensors have gained significant prominence as versatile tools for monitoring hazardous small organic pollutants in environmental, aqueous, vapor, and biological systems. This review provides a comprehensive synthesis of recent advances in the design, mechanisms, and applications of fluorescence-based probes for the detection of critical pollutants such as hydrazine, nitrosamines, aromatic amines, ethanolamine (ETA), acetone, thiophenols, pesticides, and pharmaceutical residues. Particular emphasis is placed on key sensing mechanisms, including photoinduced electron transfer (PET), intramolecular charge transfer (ICT), fluorescence resonance energy transfer (FRET), aggregation-induced emission (AIE), excited-state intramolecular proton transfer (ESIPT), and ratiometric modulation, highlighting how these principles underpin sensitivity and selectivity. Recent innovations involving small-molecule fluorophores, nanocomposites, and metal–organic frameworks are critically evaluated, with attention to their performance metrics, environmental applicability, and biocompatibility. Comparative analyses reveal significant improvements in detection limits (often reaching nanomolar levels), response times, and selectivity, while persistent challenges include photostability, reversibility, interference in complex matrices, and vapor-phase detection. Emerging integration of artificial intelligence (AI) and machine learning (ML) is also discussed as a transformative approach for sensor optimization and data interpretation. By consolidating mechanistic insights, application domains, and future prospects, this review serves as a resource for guiding the rational design of next-generation fluorescence-based sensors toward real-world deployment in environmental monitoring. • Fluorescence mechanisms (PET, ICT, AIE, FRET, ESIPT) for pollutant detection are presented. • Various fluorescent sensors for hazardous small organic molecule detection are discussed. • Paper-based, dual-mode, and vapor-phase sensors with real-world applications are examined. • Sensor designs are compared based on fluorophores, LODs, matrix tolerance, and reversibility. • AI/ML-assisted approaches for fluorophore design and real-time sensing are highlighted.