Revealing the Photodynamic Stress In Situ with a Dual-Mode Two-Photon 1O2 Fluorescent Probe.

Singlet oxygen (1O2) plays significant physiological and pathological functions, especially in causing photodynamic stress in vivo. However, specific 1O2 monitoring is an immense challenge, owing to its short half-lives and high oxidizing ability. To address this, we engineered three photostable two-photon fluorescence probe NBs for highly efficient 1O2 monitoring based on bioinspired novel tryptophan derivatives, among which NB-MOT was the best one comprehensively. Upon being cracked with 1O2, NB-MOT rapidly (within 5 s) demonstrated a remarkable enhancement in fluorescence intensity (∼180 fold) and lifetime (∼18 fold). Taking these advantages into account, NB-MOT was applied to evaluate exogenous and endogenous 1O2 in diverse biosystems. We successfully tracked the intracellular 1O2 level during photodynamic therapy, and for the first time achieved 1O2 mapping in live cells with dual-mode imaging as well as revealed ciprofloxacin-induced photodynamic stress in mice. NB-MOT was thus believed to be of instructive significance for studying the 1O2-mediated stress in wider biological milieus.