An activatable near-infrared fluorescent probe with large Stokes shift for visualizing peroxynitrite in Alzheimer's disease models.

Alzheimer's disease (AD), characterized by its incurable nature and prevalence among the elderly, has remained a focal point in medical research. Increasing evidence suggests that peroxynitrite (ONOO) serves as a crucial biomarker for the diagnosis of AD. In this study, we present a novel, easily available, high-yield, and cost-effective near-infrared (NIR) fluorescent probe, CDCI-ONOO. This probe utilizes a coumarin-dicyanoisophorone conjugate as the fluorophore and diphenylphosphinic chloride as the recognition site, enabling the detection of ONOO both in vitro and in vivo. Upon interaction with ONOO, CDCI-ONOO exhibits a distinct maximum emission peak at 715 nm with a substantial Stokes shift of 184 nm. The probe demonstrates excellent selectivity and sensitivity (LOD = 144 nM), along with noticeable colorimetric and fluorescence changes after the reaction. Comprehensive analyses using high-performance liquid chromatography (HPLC), high-resolution mass spectrometry (HRMS), and density functional theory (DFT) calculations confirm that the reaction with ONOO restores the initially quenched Intramolecular Charge Transfer (ICT), resulting in the formation of CDCI-OH, a product that emitting fluorescence in the near-infrared region. Furthermore, we demonstrated the successful application of CDCI-ONOO for ONOO detection in neuronal cells and imaging of ONOO in the brains of mice. These findings underscore the potential of CDCI-ONOO as a near-infrared fluorescent probe for in vivo ONOO detection, offering a significant avenue for advancing our understanding of AD pathology and diagnosis.