A Ratiometric Time‐Gated Luminescence Probe for Imaging H 2 O 2 in Endoplasmic Reticulum of Living Cells and Its Application to Smartphone‐Guided Bioimaging

Abstract The significance of H 2 O 2 as a marker of reactive oxygen species (ROS) and oxidative stress in living organisms has spurred growing interest in its roles in inflammation and disease progression. In this report, a ratiometric time‐gated luminescence (RTGL) probe is proposed based on mixed lanthanide complexes, ER‐BATTA‐Tb 3+ /Eu 3+ , for imaging the H 2 O 2 generation both in vitro and in vivo. Upon exposure to H 2 O 2 , the probe undergoes cleavage of the benzyl boric acid group, releasing hydroxyl (─OH) groups, which significantly reduces the emission of the Eu 3+ complex while slightly increasing the emission of the Tb 3+ complex. This response allows the I 540 /I 610 ratio to be used as an indicator for monitoring the H 2 O 2 level changes. The probes are capable of selectively accumulating in the endoplasmic reticulum (ER), allowing effective imaging of H 2 O 2 in the ER of living cells and liver‐injured mice under oxidative stress. Moreover, by integrating ER‐BATTA‐Tb 3+ /Eu 3+ into (polyethylene glycol) PEG hydrogels, the H 2 O 2 ‐responsive smart sensor films, PEG‐H 2 O 2 ‐Sensor films, are created, which enable the real‐time monitoring of H 2 O 2 levels in various wounds using a smartphone imaging platform and R/G channel evaluation. The sensor films are also innovatively applied for the in situ monitoring of H 2 O 2 in brains of epileptic rats, facilitating the precise assessment of brain damage. This study provides a valuable tool for the quantitative detection of H 2 O 2 in vitro and in vivo, as well as for the clinical monitoring and treatment of H 2 O 2 ‐related diseases in multiple scenarios.