An Ultrasensitive Lysosome-targeting NIR Fluorescence Probe for Detection of Hydroxyl Radical during Ferroptosis and Cuproptosis

Hydroxyl radical (•OH) is one of the most destructive reactive oxygen species in biosystems, mainly produced by the participation of transition metals. Lysosomes, the major metabolic center of intracellular metals, may accelerate the generation of •OH by metal-participated reactions due to their acidic microenvironment, which may make lysosomes a major intracellular site for •OH production. In this work, an ultrasensitive NIR lysosome-targeting •OH fluorescence probe, Lyso-OH, was developed for in situ detection of •OH in lysosomes. The reaction of Lyso-OH and •OH leads to a large spectroscopic red-shift and a significant NIR fluorescence response at 655 nm. Such large changes in π-conjugation and spectroscopic properties can achieve an extremely low background fluorescence, which is helpful to obtain a high-contrast and ultrasensitive NIR fluorescence response, enabling Lyso-OH to detect the trace •OH produced by autoxidation of low-valent metals (e.g. Fe²⁺ and Cu⁺). Lyso-OH has good lysosome-targeting ability and has been used for the fluorescence imaging of two transition metal-dependent regulated cell death processes, ferroptosis and cuproptosis. The results revealed that both ferroptosis and cuproptosis were accompanied by lysosomal •OH level increase. Moreover, Lyso-OH was also capable of monitoring the •OH level fluctuations in mice models of inflammation and tumor. The good analytical performance of Lyso-OH may allow it to be widely used in more •OH-associated physiological and pathological processes.