Fig. 7. Fluorescence responses of GCS-2 and mCherry co-expressed in HeLa cells to 10 μM Cu²⁺. (a) Images of GCS-2 (top) and mCherry (bottom) of 1 min prior to Cu²⁺ addition and 4 min after the addition of Cu²⁺. Scale bar: 10 μm (b) plots of the average fluorescence responses of GCS-2 and mCherry of 8 cells vs. time after 10 μM Cu²⁺ addition. All fluorescence intensity values were subtracted by background signals and normalized by the fluorescence before Cu²⁺ addition. The error bars correspond to the standard error of the mean value of eight individual cells.