Benzoyl peroxide (BPO), a member of small-molecule reactive oxygen species (ROS), has attracted considerable attention because of its impact on human health and industrial importance. Herein, to quantitatively detect BPO in real samples and for fluorescence imaging of BPO in living cells and tissues, a new water-soluble two-photon (TP) fluorescent probe (CM-1) was constructed. Specifically, CM-1 comprises the carboxyl (-COOH) group as the water-soluble unit, cyano (-CN) group that forms the D-pi-A-structure as an acceptor to increase the two-photon action absorption cross-section and phenylbor...