In summary, a fluorogenic rhodamine-lactam pH sensor,
Rlyso, exhibited high selectivity and sensitivity for intracellular
pH, as well as low cytotoxicity and high photostability. It can
selectively stain lysosomes in live cells. This staining ability is
due to the presence of the methylcarbitol group, which avoids
the ‘‘alkalizing effect’’ on lysosomes by the current lysosomal
sensors with nitrogen-containing sidechains. Importantly,
Rlyso was used to quantitatively detect the chloroquine-
induced increase in lysosomal pH and monitor changes in
the acidity of lysosomes during apoptosis in live cells.
Fig. 3 Fluorescence images of Rlyso in mouse macrophages stimulated
with chloroquine. (a–c) Images of the stained cells before chloroquine-
stimulation; (d–f) images of cells in (a–c) exposed to 100 mM chloroquine
for 2 min. (g) Relative fluorescence intensity values. The probe was
excited at 559 nm and the fluorescence was collected at 575–620 nm.
This work was supported by NSF of China (21136002,
2107603 and 20923006), National Basic Research Program
of China (2009CB724706 and 2013CB733702), Scientific
Research Fund of Liaoning Provincial Education Department
(LS2010040). We also gratefully acknowledge Dr Richard
Horobin from the University of Glasgow for valuable discussion.
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MTT assays revealed that the cell viabilities of HeLa cells
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c
11768 Chem. Commun., 2012, 48, 11766–11768
This journal is The Royal Society of Chemistry 2012