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Fig. 2 PCO-1 showed a robust and selective turn-on response to CO in
reaction buffer pH 8.0 at 37 1C (ex: 340 nm) mediated by PdCl2. (a)
Fluorescence responses of PCO-1 (10 mM) to various levels of CORM-3
observed at 0, 5, 10, 15, 20, 25 and 30 minutes in the presence of 10 mM
PdCl2. (1) None, (2) PdCl2, (3) 50 mM CORM-3, (4) PdCl2 + 1 mM CORM-3,
(5) PdCl2 + 5 mM CORM-3, (6) PdCl2 + 10 mM CORM-3, (7) PdCl2 + 20 mM
CORM-3 and (8) PdCl2 + 50 mM CORM-3. (b) Fluorescence responses of
10 mM PCO-1 to CO in the presence of PdCl2 (10 mM) and various species
observed at 0, 5, 10, 15, 20, 25 and 30 minutes. (1) None, (2) CORM-3,
(3) NO (source NOCl3ꢀ), (4) H2S (source NaHS), (5) NaOCl, (6) H2O2,
Fig. 3 Fluorescence microscopy images of A549 cells for CO detection
using PCO-1 (10 mM) in the presence of 10 mM PdCl2 with the incubation of
(a) 10 mM, (b) 20 mM and (c) 50 mM of CORM-3 in the reaction buffer at
37 1C (ex: H340 nm). The first and second rows represent the phase
contrast and fluorescence images respectively.
t
ꢂ
concomitant increase of fluorescence intensity by 150 times.
The response is selective over a variety of relevant reactive
nitrogen, sulfur and oxygen species and can be used to image
CO in living cells.
Financial assistance from Department of Science and Tech-
nology (DST), New Delhi, Govt. of India, for providing Fast track
research grant (vide project no. SB/FT/CS-142/2012) is gratefully
acknowledged.
(7) BuOOH and (8) O2 (source KO2).
that the reaction of CO is initiated by the in situ generated Pd(0)
species. Addition of 50 mM CORM-3 to a solution of 10 mM PCO-1 in
the presence of 10 mM PdCl2 at 37 1C produced a robust fluores-
cence ‘turn-on’ response by more than 150-fold higher fluores-
cence. A variable pH dependency study of fluorescence indicated
that the maximum enhancement was observed in the range of pH 8
(Fig. S9, ESI†). Moreover we observed the dose dependent
responses toward CORM-3 down to a 1 mM (B28 ppb CO) level
(Fig. 2a). The limit of detection (LOD) of CO was calculated as
8.49 nM using the 3s method (Fig. S10, ESI†). In addition, the
fluorescence ‘turn-on’ response to CORM-3 shows good selectivity
over a variety of biologically relevant reactive nitrogen, sulfur and
oxygen species, including NO, H2S, NaOCl, H2O2, tert-butyl hydro-
peroxide (tBuOOH) and superoxide (O2ꢀ). The introduction of these
molecules did not trigger any fluorescence enhancement as it
happened in the case of CO (Fig. 2b).
Finally to visualize CO levels in live cells we examined a
fluorescence microscopy experiment with PCO-1 (Fig. 3). A549
human lung carcinoma cells were incubated with 10 mM PCO-1
and CORM-3 (10, 20 and 50 mM) in the presence of 10 mM PdCl2
(Fig. 3) at 37 1C. A dose-dependent intracellular fluorescence
was observed in the case of CORM-3 over the control experi-
ment (Fig. S11, ESI†). The fluorescence images with the corres-
ponding phase contrast images also demonstrated the different
fluorescence distribution of CO molecules inside the cells using
various concentrations of CORM-3. In addition to that, 10 mM of
PCO-1 did not show any significant cytotoxic effect (Fig. S12,
ESI†) on A549 human lung carcinoma cells for at least up to 4 h
of its treatment though there was significant cytotoxicity for
higher doses after 4 h onward. These results indicated that the
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