A two-photon fluorescence probe with endoplasmic reticulum targeting ability for turn-on sensing photosensitized singlet oxygen in living cells and brain tissues

Endoplasmic reticulum (ER) is an indispensable organelle responsible for protein synthesis , transportation, and maintenance of Ca 2+ homeostasis in eukaryotic cells. Recent studies highlighted that ER-targeted photosensitizers with high yield of singlet oxygen ( 1 O 2 ) are effective in selectively disrupting ER function and are promising candidates for anticancer therapy. Unfortunately, no ER targetable fluorescent probes for determining 1 O 2 photosensitized in this photodynamic therapy process is available. In this work, we synthesized an ER-targetable, two-photon fluorescence probe, ER- 1 O 2 , for fluorescence turn-on sensing of 1 O 2 . ER- 1 O 2 demonstrated high sensitivity to 1 O 2 sensing with a wide detection range (0–2.75 μM) and a low detection limit (0.11 μM). ER- 1 O 2 also displayed excellent selectivity toward 1 O 2 out of other ROS and metal ions . Notably, ER- 1 O 2 exhibited low cytotoxicity but with specific ER targetable capability. On account of these advantageous features, fluctuations of 1 O 2 in living cells and brain tissues were effectively visualized by ER- 1 O 2 .