Off-On Fluorescent Nanomaterial-Based Sensors for Food Quality and Safety Assessment: Recent Advances and Future Perspectives

Abstract

Food quality and safety monitoring has become increasingly important due to the growing risk of contamination by pesticides, veterinary drug residues, pathogenic microorganisms, heavy metals, and mycotoxins. Conventional analytical methods, although highly accurate, often require expensive instrumentation, complex sample preparation, and skilled operators, limiting their application in rapid and on-site analysis. In recent years, nanomaterial-based fluorescent sensors have emerged as promising alternatives because of their high sensitivity, rapid response, portability, and low detection limits. Among them, off–on fluorescent sensors have attracted considerable attention owing to their enhanced selectivity and reduced matrix interference. These sensing platforms operate through an initial fluorescence quenching step followed by fluorescence recovery in the presence of target analytes. The sensing mechanisms are commonly based on fluorescence resonance energy transfer (FRET), photoinduced electron transfer (PET), and the inner filter effect (IFE). This review summarizes major fluorescent nanomaterials employed in off–on sensors, including quantum dots, carbon dots, and metal nanoclusters. Furthermore, key sensing strategies such as redox reactions, competitive coordination, DNA hybridization, and enzyme-mediated recognition are discussed. Recent applications in the detection of veterinary drugs, pesticide residues, foodborne pathogens, mycotoxins, and heavy metal ions are highlighted. Finally, current challenges and future perspectives for the development of portable, highly sensitive, and practical sensing platforms for food quality and safety assessment are presented.