Fluorescence response of 1-4 (A: 1, B: 2, C: 3, D: 4, 0.3 μM) in SDS, CTAB and TX-100 micelle solutions (50 mM in PBS) at different pHs. No fluorescence in the MeOH solutions of dye + surfactant except for 4 (data not shown). The fluorescence is normalized to FL = 100 under acidic conditions for each dye.