Chemodosimeter-based fluorescent probes for esterase, nitroreductase and tyrosinase

Cellular functions are governed by intricately coordinated biochemical pathways mediated by diverse enzymatic transformations. In recent years, significant efforts have been devoted to developing molecular imaging tools, including small-molecule probes, dye-conjugated biomolecules, and genetically encoded fluorescent biosensors, to visualize these processes with high spatial and temporal resolution. Among these approaches, chemodosimeter-based fluorescent probes have emerged as powerful platforms owing to their high sensitivity, selectivity, and irreversible signal generation upon specific enzymatic reactions. These activity-based probes undergo distinct chemical transformations in the presence of target enzymes or enzyme-generated metabolites, enabling real-time fluorescence "turn-on" responses that facilitate the direct monitoring of enzymatic activity in complex biological environments. Such fluorescent chemodosimeters have been extensively employed for investigating enzyme-mediated biochemical pathways in both in vitro and in vivo systems. Importantly, recent advances demonstrate their potential for detecting aberrant enzyme expression and activity associated with pathological conditions, thereby expanding their utility in clinical diagnostics, disease monitoring, and chemical biology. The integration of molecular design strategies with advanced bioimaging methodologies has further accelerated the development of highly selective and biocompatible probes for targeted enzymatic sensing. In this review, we summarize recent progress in chemodosimeter-based fluorescent probes designed for the detection and imaging of three biologically and clinically significant enzymes-esterase, nitroreductase, and tyrosinase. Particular emphasis is placed on probe design principles, sensing mechanisms, photophysical properties, and biological applications in cellular and living systems. We also discuss current challenges and future perspectives for the development of next-generation fluorescent chemodosimeters for enzymatic bioimaging and activity-based diagnostics. Beyond summarizing recent developments, this review provides a comparative perspective on the molecular design strategies employed for three representative enzyme classes that catalyze hydrolytic, reductive, and oxidative transformations. By highlighting common design principles, sensing mechanisms, and current limitations, this review offers practical insights for the rational development of next-generation activity-based fluorescent probes for chemical biology, disease diagnosis, and precision bioimaging.