Construction of a Turn Off-On-Off Fluorescent System Based on Competitive Coordination of Cu²⁺ between 6,7-Dihydroxycoumarin and Pyrophosphate Ion for Sensitive Assay of Pyrophosphatase Activity

Figure 2

(a) UV-Vis absorption responses of DHC (500 μM) upon the addition of different concentrations of Cu²⁺ (0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 2.0, 3.0, 4.0, 5.0, 7.0, and 10.0 equiv.) in HEPES buffer aqueous solution (10 mM, pH 6.5). Inset: the corresponding changes of absorbance of DHC at 375 nm in the presence of different concentrations of Cu²⁺. (b) Fluorescence titration of DHC (500 μM) with Cu²⁺ (0, 10, 30, 50, 70, 100, and 200 μM) in HEPES aqueous buffer (10 mM, pH 6.5). Inset shows fluorescence intensity changes of DHC at 475 nm as a function of the Cu²⁺ concentration. Other reaction conditions are the same as Figure 1.

(a)

(b)