Visual
detection of mercury ions and glutathione is of great significance
to public health and environmental issues. Herein, we developed a
fluorescent sensor (l-Cys/CuNCs@ESM) based on the eggshell membrane
(ESM) and red-emitting copper nanoclusters (CuNCs) by the in situ
strategy via l-cysteine (l-Cys) as the reducing
and protective agent for mercury ions and glutathione sensing visually.
The as-prepared fluorescent product had good stability, portability,
large Stokes shift (250 nm), and long fluorescence lifetime (7.3 μs).
Notably, the l-Cys/CuNCs@ESM exhibited a specific fluorescence
quenching response toward Hg2+. Moreover, the interaction
between glutathione (GSH) and Hg2+ could subsequently recover
the fluorescence effectively. Inspired by this “on-off-on”
switch, the l-Cys/CuNCs@ESM was applied as the dual-sensing
system for visual detection of mercury ions and glutathione integrating
with the portable smartphone. The limit of detection (LOD) of Hg2+ is 1.1 μM for visualization and 0.52 μM for
the fluorescence spectrometer. The corresponding LODs of GSH are 2.8
and 0.59 μM, respectively. This platform presents significant
sensitivity, specificity, and stability, offering a promising potential
for real-time/on-site sensing.