Research progress on design strategies of hemicyanine-based fluorescent probes and their applications in environmental and food analysis

With the increasing emphasis on environmental safety, food inspection, and plant physiological functions, the development of high-performance fluorescent probes capable of highly sensitive, specific, rapid, and visual detection of target analytes has become a focal point in current research. Hemicyanine groups are widely utilized in the design of organic small-molecule fluorophores due to their low cost, structural stability, and ease of chemical modification. Through simple structural adjustments, the photoluminescent properties of hemicyanine-based fluorophores can be significantly enhanced, enabling strong signal output and maintaining stable fluorescence intensity across various solvents and pH conditions-features that make them particularly suitable for complex biological and chemical environments. Furthermore, the nitrogen atoms of the hemicyanine groups can be functionalized with various water-soluble and targeting groups, which greatly improve molecular hydrophilicity. In recent years, small-molecule fluorescent probes based on hemicyanine groups have been successfully applied in the reliable detection of metal ions, cyanide, sulfide, hydrazine, phosgene, nitrite, hypochlorous acid, and other analytes. This review provides an overview of the structural features of hemicyanine fluorophores and systematically summarizes the design strategies, sensing mechanisms, and recognition principles of hemicyanine-based probes. It further details recent advancements over the past five years, categorized by different analytes, with particular emphasis on their applications in environmental monitoring, food safety, and plant science. Finally, based on a comprehensive analysis of existing research, this review highlights the strengths and limitations of these fluorescent probes and offers constructive insights for future studies, aiming to provide a valuable reference for the continued advancement of hemicyanine-derived fluorescent sensing systems.