Inorganic Chemistry Communications
A novel selective fluorescent and colorimetric chemosensor for the visual
detection of Pd2+ and application of imaging in living cells
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Meipan Yang, Yinjuan Bai, Wenfei Meng, Zhao Cheng, Na Su, Bingqin Yang
Key Laboratory of Synthetic and Natural Functional Molecule Chemistry, Ministry of Education, College of Chemistry and Materials Science, Northwest University, Xi'an 710069, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A rhodamine-based fluorescent chemosensor was synthesized and characterized, which demonstrated excellent
specificity toward Pd2+. Upon addition of Pd2+, the ring-opening process of rhodamine spirolactam resulted in
remarkably enhanced fluorescent accompanied by distinct color changes. Commonly coexistent metal ions
displayed little interference to the sensor. Obviously, these unique results suggested that the chemosensor
could serve as a potential naked-eye sensor for Pd2+. The detection limit was 0.19 μM. In addition, we prepared
the test strips of sensor for Pd2+ detection, which provided a simple and convenient method for determination of
Pd2+ in palladium-containing water samples. Importantly, the sensor was successfully used for fluorescence im-
aging in HepG2 cells.
Received 24 April 2014
Received in revised form 7 June 2014
Accepted 25 June 2014
Available online 26 June 2014
Keywords:
Pd2+
Chemosensor
Naked-eye
Test strips
Bioimaging
© 2014 Elsevier B.V. All rights reserved.
Among the rare transition metals, palladium plays a critical role in
materials and chemistry. It is extensively being used to prepare dental
crowns, catalytic converters, fuel cells, alloys and jewelry [1–3]. At the
same time, Pd-catalyzed reactions are becoming increasingly popular
in pharmacy because of the powerful transformations for the synthesis
of complex molecules [4–7]. However, their large use leads to a high
level of residual palladium. For example, the release of palladium from
catalytic converters of automobiles results in a great quantity of palladi-
um in complex environmental system, from soil to plants, rivers and
oceans, which also influences our health in an adverse way [8–11]. Gov-
ernmental restrictions on the levels of residual heavy metals in end
products are very rigorous and strict. The proposed dietary intake of pal-
ladium is less than 1.5–15 μg/day per person and the threshold in drugs
is 5–10 ppm [12]. Thus, a considerable effort has been devoted to the de-
velopment of the efficient methods to detect and analyze palladium.
Conventional detection methods include atomic absorption spectrosco-
py (AAS), atomic emission spectrometry (ICP-AES), X-ray fluorescence
etc., which usually require sophisticated instrumentation and compli-
cated sample-pretreatment procedures [12–15]. Fluorescence analysis
offers significant advantages over other methods for metal ion detection
due to its simplicity, high sensitivity, low cost and instantaneous re-
sponse [16–21]. Whereas most of the reported Pd2+ fluorescent
chemosensors show “on–off” signal upon the binding of Pd2+ due to
the fact that it usually acts as typical fluorescence quenchers, which is
not as sensitive as a fluorescence enhancement response [22–25]. Im-
portantly, most reported “off–on” fluorescent chemosensors have not
been applied to detecting Pd2+ in biological systems [26–30]. Therefore,
it is still an outstanding challenge to create new “off–on” fluorescent
Pd2+ chemosensors which demonstrated value of practical applications
in biological systems.
Recently, a number of research groups have proposed various
chemosensors based on rhodamine conjugates [31–42]. Rhodamine
derivatives provide an ideal model for the design of metal ion sens-
ing with light “off–on” switching by virtue of the equilibrium be-
tween spirolactam (nonfluorescence) and ring-opened amide
(fluorescence) forms. For our role, here we presented the design
and synthesis of sensor R1, which can be used for “naked-eye” detec-
tion with the switch-on fluorescence and significant color changes.
The sensor showed highly sensitive spectroscopic response to
Pd2+. Soaked on paper, R1 exhibited an acute color response,
which provided a simple and convenient method for determination
of Pd2+ in palladium-containing water samples. What's more, the
bioimaging capability of the sensor was further tested successfully
in HepG2 cells.
The chemosensor R1 was prepared by using a two-step procedure
(See Scheme 1.) High selectivity for the analyte and suitability of the
sensor are crucial in designing modern chemosensors. In Fig. 1, the
color-on reaction of R1 showed a high selectivity toward Pd2+ only,
rather than other examined ions, such as Fe3+, NH+4 , Sn2+, Ag+, Ba2+
,
Al3+, Cd2+, Cr3+, Cu2+, Hg2+, K+, Mg2+, Mn2+, Na+, Ni2+, Pb2+ and
Zn2+. These unique results suggested that R1 could serve as a potential
naked-eye chemosensor for Pd2+. The UV–vis and fluorescence proper-
ties of R1 were investigated toward different cations in methanol/PBS
(1:1, v/v, pH 7.4) solution (Fig. S1). Interestingly, upon addition of
Pd2+ to the solution of chemosensor, a significant absorbance appeared
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Corresponding author.
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