A mitochondrial-targeted red fluorescent probe for detecting endogenous H2S in cells with high selectivity and development of a visual paper-based sensing platform

•SXR showed obvious signal enhancement in red spectral window (>600 nm) in a dose dependent manner.•SXR showed rapid response (∼6 min), excellent selectivity and large Stokes shift (∼90 nm) to H2S.•Cytotoxicity test indicated that probe SXR had very slight cytotoxicity even at the concentration of 100 μM.•The mitochondrial-targeted detection of exogenous and endogenous H2S was successfully actualized by using SXR.•A portable, economic and visual sensor for monitoring H2S was developed by integrating SXR immobilized filter paper with smart phone.