“…33 Application of FZ-3 in monitoring other transition metals revealed a turn-on fluorescent response with other substrates such as Fe( ii ), Co( ii ), Ni( ii ) and Cd( ii ) in the presence and absence of lipids. 35,36 However, in the putative application of FZ-3 to detect Ni( ii ) transport activity by NixA in proteoliposomes potential problems were encountered related to: (i) residual Zn( ii ) contamination in lipids isolated from native sources, and (ii) the FZ-3 significantly higher sensitivity for Zn( ii ) compared to Ni( ii ), which would affect batch-to-batch reproducibility. To circumvent these potential problems, we decided to exploit the comparable affinities of FZ-3 for Zn( ii ) and Ni( ii ) (or Co( ii )), and the significantly lower fluorescent turn-on response (fluorescence yield) for FZ-3-Ni( ii )/Co( ii ) complexes (compared to FZ-3-Zn( ii )).…”