Lanthanide Complex-Based Probes for Ratiometric Time-Gated Luminescence and 19F Magnetic Resonance Imaging of Hydrogen Peroxide In Vitro and In Vivo.

Fluorescent bioimaging is a key technique for real-time and in situ visualization of bioactive species in living organisms. However, its utility for in vivo applications is often limited by a low tissue penetration depth. Herein we report novel lanthanide complex-based probes, a ratiometric time-gated luminescence (TGL) probe, Mito-PFTTA-Eu3+/Tb3+, and a 19F magnetic resonance (MR) probe, Mito-PFTTA-Gd3+, for the highly sensitive and in situ detection of hydrogen peroxide (H2O2) in biological samples. To construct the probe, we first designed and synthesized a multifunctional ligand, (4'-pentafluorobenzenesulfonate-2,2':6',2''-terpyridine-6,6''-diyl) bis(methylenenitrilo)tetrakis(acetic acid) (Mito-PFTTA), by integrating a mitochondria-anchoring motif, triphenylphosphonium cation and a H2O2-responsive pentafluorobenzenesulfonate (PFBS) moiety into a terpyridine polyacid framework. Then a mixture of its Eu3+ and Tb3+ complexes, Mito-PFTTA-Eu3+/Tb3+, were developed as a ratiometric TGL probe for H2O2 detection. In parallel, its Gd3+ complex, Mito-PFTTA-Gd3+, was constructed as an 19F NMR probe for H2O2 sensing. Upon reaction with H2O2, the PFBS group is cleaved from the complex, leading to opposite changes in the emission intensity: an increase in the Tb3+ emission at 540 nm and a decrease in the Eu3+ emission at 610 nm. These changes allow Mito-PFTTA-Eu3+/Tb3+ to serve as a ratiometric TGL probe for H2O2 detection using the I540/I610 ratio as a signal output. Thanks to its excellent mitochondrial targeting capability and excellent biocompatibility, Mito-PFTTA-Eu3+/Tb3+ enabled the ratiometric TGL imaging of mitochondrial H2O2 in living cells and in the livers of mice with drug-induced liver injury. Additionally, the 19F NMR signal of Mito-PFTTA was effectively quenched upon complexation with Gd3+ ions, but was restored upon H2O2-triggered PFBS cleavage. This behavior allowed Mito-PFTTA-Gd3+ to function as a 19F MRI probe for detection of H2O2 in vitro and in vivo.