Figure 2.
Fluorescence correlation spectra of dsRed. (a) Excitation intensity dependence of photoconversion kinetics of dsRed (pH 9.0) FCS correlation curves as a function of kex at 488 nm (≈0.4–7.3 kW/cm2). (b) Light-driven fluorescence flicker fraction and (c) rates of dsRed. The dark fraction (f1 = 0.30 ± 0.04) appears constant below saturation (with a minor decline at low kex and the rate depends linearly on intensity with a slope of (2.9 ± 0.2) × 10−3 and an intercept of 400 ± 30 Hz as kex→0. Autocorrelation spectra of dsRed (a) at low kex show lack of pH dependence in the pH range 3.9 to 11. (d) The fluorescence flicker rate (1.7 ± 0.1 × 103 s−1) and dark fraction (0.41 ± 0.03) are clearly independent of pH.