Fig. 2.

Spectroscopic responses and selectivity of CS3. All spectra were acquired in 20 mM HEPES, pH 7, at 25 °C. (A) Fluorescence response of 4 μM CS3 to Cu⁺. Spectra shown are for buffered [Cu⁺] of 0, 0.3, 0.5, 0.8, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, and 4.0 μM. (B) Fluorescence responses of CS3 to various metal ions. Bars represent the final integrated fluorescence response (F_f) over the initial integrated emission (F_i). White bars represent the addition of an excess of the appropriate metal ion (2 mM for Ca²⁺, Mg²⁺, and Zn²⁺; 50 μM for all other cations) to a 4 μM solution of CS3. Black bars represent the subsequent addition of 4 μM Cu⁺ to the solution. Excitation was provided at 530 nm, and the collected emission was integrated over 540 to 700 nm.