Figure 2. Ratiometric fluorescence response of RHP-2 to sulphide.

(A) Fluorescence spectra of RHP-2 (5 μM) with Na₂S (0, 2, 4, 8, 10, 15, 20, 30, 40, 60 and 100 μM) in PBS buffer (20 mM, pH = 7.4, 5% CH₃CN) at 37°C for 40 min. Insert: Photograph showing the visual fluorescence of RHP-2 without (a) or with (b) Na₂S under a 365-nm UV lamp. (B) Emission intensity ratios of RHP-2(5 μM) after 40 min of incubation with different concentrations of Na₂S (0 to 400 μM) in PBS buffer (20 mM, pH = 7.4, 5% CH₃CN) and foetal bovine serum (5% CH₃CN). Insert: The linear relationship between the emission intensity ratios (F₅₃₂/F₄₆₇) and the concentrations of Na₂S (0 to 100 μM) in PBS buffer and foetal bovine serum. Data are presented as the mean ± SD (n = 3).