Fig. 4. Two-photon imaging of rat liver slices upon excitation at 780 nm with femtosecond pulses: (a–c) liver slice incubated with TR-H₂S (5 μM) for 30 min, emission measured at 471–560 nm (a) and 591–704 nm (b); (c) the ratio of (a) and (b); (d–f) liver slice incubated with TR-H₂S (5 μM) for 30 min and then further incubated with H₂S (100 μM) for 30 min, emission measured at 471–560 nm (d) and 591–704 nm (e); (f) the ratio of (d) and (e). Scale bars: 100 μm.