Figure 2. In vitro characterizations of engineered Zn2+ sensors.
(A) Zn2+ titration curves for ZnGreen1 (gray, filled circle), ZnGreen2 (gray, open circle) and ZnRed (black, filled circle). Curves were fit according to the equations described in Supporting Information, assuming a single-binding mode for ZnGreen1 and ZnGreen2 and a double-binding mode for ZnRFP. (B) Fluorescence responses of ZnGreen1 (black bar), ZnGreen2 (white bar) and ZnRed (gray bar) to various metal ions, showing excellent selectivity toward Zn2+. The final metal concentrations were 20 μM for Zn2+ and 100 μM for all other metals and EDTA. Fluorescence intensities were normalized to blank samples (BLK, no metal ion added).