DOI: 10.1002/asia.201500767
Communication
Fluorescent Probes
A Highly Sensitive Fluorescent Sensor for Palladium and Direct
Imaging of Its Ecotoxicity in Living Model Organisms
Fei Liu, Juan Du, Meiying Xu,* and Guoping Sun[a]
allylic oxidative insertion reaction.[7] Based on palladium-cata-
Abstract: Rhodamine is an ideal platform for fluorescence
probes owing to its spiro-lactam framework and excellent
lyzed chemical conversion, Ahn’s group synthesized a turn-on
fluorescent probe that was used to fluorescently sense palladi-
photochemical properties. Herein, a novel rhodamine-
um species in all of its typical oxidation states (0, +2 and +4)
based palladium fluorescent chemosensor, Rd-Eb, show-
and to monitor Pd2+ in living zebra fish for the first time.[8]
ing a fast response time (3 min), high sensitivity for palla-
Hereafter, Peng et al. reported a series of rhodamine hydrazone
dium species over other ions, and a low detection limit
(1.9110À7 m), was synthesized. It can act as an obvious
colorimetric as well as a fluorescent “off/on” sensor for
derivative palladium probes that showed good coordination
with Pd2+ and less interference from other ions; the analysis of
Pd2+-contaminated water and soil samples demonstrated the
Pd2+. In addition, it is also an excellent sensor for in vivo
potential usefulness of these probes.[9] The use of several fluo-
imaging of Pd2+ in zebra fish and Daphnia magna, illumi-
rescent probes has been reported for the detection of palladi-
nating the impact of palladium on organisms at different
um in living cells, with good selectivity for palladium in in vitro
growth stages with respect to biological toxicology.
assays and in vivo imaging studies.[10] However, very few sen-
sors have been used for the bioimaging of palladium in living
organisms and for visually illuminating the impact of palladium
Because of its specific physicochemical properties, palladium
has been widely used in various materials,[1] which has resulted
in the release of large amounts of residual palladium into the
environment in the past few decades.[2] Palladium can have
negative influences on our health by disturbing a variety of
cellular processes through its binding to thiol-containing ami-
noacids, proteins (e.g., casein, silk fibroin, and many enzymes),
DNA, and other macromolecules. Even at very low concentra-
tions, palladium can cause allergic reactions in susceptible indi-
viduals.[3] Governmental restrictions on the levels of residual
heavy metals in end products are very strict (less than 5–
10 ppm).[4] Thus, considering the serious toxicity and other ad-
verse effects of palladium, exploring highly sensitive and selec-
tive methods for its detection is urgent.
on organisms at different growth stages with respect to bio-
logical toxicology. The use of a fluorescent probe to visualize
the distribution of palladium in living organisms is very signifi-
cant and innovative, which may prove to be a useful tool in
the field of biological toxicology research.
Herein, as shown in Scheme 1, a new rhodamine-based
highly sensitive and selective fluorescent chemosensor Rd-Eb
for the analysis of palladium is presented. Rd-Eb can selectively
detect palladium species (Pd2+ and Pd0 states) among other
metal species and trigger the hydrolysis of Rd-Eb+Pd2+ when
water is present in the solution. Alkyne groups as the coordi-
nating ligands for palladium were used in some fluorescent
sensing systems; hence, it could attach onto the colorless spi-
rolactam ring of rhodamine, leading to a purple color and
emission of strong fluorescence of the rhodamine dye.[11] This
sensor showed high sensitivity for Pd2+ ions compared to
other platinum group element (PGE) ions. Furthermore, this
probe enabled us to trace the primary route of palladium in
live aquatic organisms, such as zebra fish and Daphnia magna,
and compare it to the toxicology of Pd2+ in these organisms.
To our knowledge, this is the first time Daphnia Magna is
being used for Pd2+ fluorescent imaging.
As shown in Figure 1a, upon addition of Pd2+ to EtOH/H2O
solutions (1:1, v/v) of Rd-Eb, a strong absorption band cen-
tered at 560 nm with an apparent pink coloration was ob-
served, which indicated that the Pd2+-promoting ring opening
reaction took place quickly. To determine the response time of
the Rd-Eb probe for Pd2+, a time-dependent experiment was
conducted. As shown in Figure S1 in the Supporting Informa-
tion, the response time of the reaction system was about
3 min after which fluorescence saturation was attained in the
The conventional analytical methods for palladium include
atomic absorption spectrometry (AAS), inductively coupled
plasma–mass spectrometry (ICP-MS), X-ray fluorescence, etc.[5]
However, these methods suffer from a high cost of sample
preparation and require expensive equipment and highly
trained operators. Recently, the fluorescent method has
become more desirable for palladium analysis and has fre-
quently been applied because of its low cost, simplicity, and
high sensitivity.[6] The group of Koide reported a fluorescent
sensing system for Pd0 based on the Pd0-catalyzed Tsuji–Trost
[a] F. Liu, J. Du, Prof. M. Xu, Prof. G. Sun
State Key Laboratory of Applied Microbiology Southern China
Guangdong Institute of Microbiology
100 Central Xianlie Road, Guangzhou 510070 (P.R. China)
Supporting information and ORCID(s) from the author(s) for this article are
Chem. Asian J. 2016, 11, 43 – 48
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