In addition, the
fluorescence titration profile also demonstrates that R has a
detection limit of 0.272 nM (17.3 ppb) for Cu2+ and 0.252 nM
(16.5 ppb) for Zn2+ ions (Figure S12 in the SI), which are
comparable to the other reported Cu2+ and Zn2+ chemosensors,
and this level of the detection limit is
sufficient to sense Cu2+ and Zn2+ ions even in biological
systems because the average concentration of Cu2+ in blood is
100−150 μg L−1 (15.7−23.6 μM).23