<scp>HKOH</scp> ‐2 Series Probes for Imaging Hydroxyl Radical in Living Cells With Subcellular Precision and In Vivo

ABSTRACT Hydroxyl radical ( • OH) is the most reactive and deleterious reactive oxygen species, yet its direct detection remains highly challenging because of its extremely short lifetime and high reactivity. Here we report the HKOH‐2 series of fluorescent probes for imaging • OH in living cells, rat brain slices, and living zebrafish. In addition, HKOH‐2L and HKOH‐2m were developed for selective detection of • OH with organelle resolution in lysosomes and mitochondria, respectively. The HKOH‐2 series thus provides versatile chemical tools for monitoring local • OH production in living cells and in vivo.