Nitroreductase-Activated Fluorescent Probes: From Molecular Design to Disease Diagnosis.

Nitroreductases (NTRs), a class of flavin-dependent oxidoreductases, are highly upregulated in hypoxic microenvironments and are closely associated with cancer, bacterial infections, and other hypoxia-driven diseases. Precise and real-time visualization of NTR activity is therefore critical for understanding disease mechanisms and enabling accurate diagnosis and targeted therapy. Fluorescent probes have emerged as powerful and versatile chemical biology tools for NTR sensing owing to their high sensitivity, selectivity, and spatiotemporal resolution. Recent advances in two-photon fluorescence imaging, second near-infrared (NIR-II) fluorescence imaging, and time-resolved fluorescence imaging have markedly enhanced tissue penetration and quantitative accuracy, thereby enabling reliable detection of NTR activity in complex biological environments. This review summarizes representative advances over the past 5 years in the molecular design of NTR-responsive probes, with emphasis on recognition motifs, signal transduction strategies, and structure-function relationships that determine selectivity and sensitivity. Disease-oriented applications in cancer, bacterial infections, and other hypoxia-associated disorders-including myocardial ischemia, inflammatory bowel disease, pulmonary fibrosis, and infertility-are discussed. Finally, current challenges and future opportunities are outlined to guide the development of next-generation NTR-responsive probes for high-fidelity imaging and precision theranostic applications.