Journal of the American Chemical Society
Communication
media. In the first 25 min, as incubation time elapses, the
fluorescence intensity increases with the progress in the probe
binding to integrin αvβ3. The green fluorescence from the
probe overlaps well with the red fluorescence from the
membrane tracker. Clearly, during this period of time, most
of the bound probes are localized on the cell membranes.
Longer incubation time (>25 min) results in gradual internal-
ization of the probe. In addition, HPLC analysis reveals that the
probe has good stability in the cellular environment for 2 h (SI
Figure S8). Collectively, these results show that TPS-2cRGD
not only can be used for the detection of integrin αvβ3-positive
cancer cells, but also has the potential to become a powerful
bioprobe for studying interaction with integrin αvβ3 and tracing
the integrin αvβ3 internalization in a real-time manner.
Cytotoxicity of the fluorescent probe was evaluated by the
widely used MTT assay. As shown in SI Figure S9, after being
incubated with TPS-2cRGD at concentrations of 2, 5, and 10
μM for 12, 24, and 48 h, the HT-29 cells remain ∼100%
metabolically viable under the testing conditions, indicative of
excellent cyto-compatibility of the fluorescent probe.
In summary, a cRGD-conjugated probe has been developed
in this work. Thanks to its novel AIE nature, the probe is
nonfluorescent in the aqueous buffer but becomes emissive
when bound to integrin αvβ3, which enables integrin detection
with little background interference. The binding affinity of
TPS-2cRGD to HT-29 over MCF-7 demonstrates its potential
as a specific probe for discriminating integrin αvβ3-positive
cancer cells from integrin αvβ3-negative cancer cells. To the
best of our knowledge, this is the first fluorescence light-up
probe for the detection of endogenous human integrin receptor
in live cells. It also represents the first AIE bioprobe for specific
real-time biomarker imaging, which opens new avenues for
continuous monitoring of biological events. Our AIE probe
strategy can be generalized to perform various tasks by simply
changing peptide into other biorecognition units, such as
antibodies, aptamers, and ligands. Further tuning the emission
spectrum of the AIE fluorogen to red and near-IR region will
facilitate the development of specific bioprobes for in vivo
tumor diagnosis.
of Materials Research and Engineering of Singapore (IMRE/
11-1C0213).
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in DMSO/water and in cell culture medium; stability and
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AUTHOR INFORMATION
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Corresponding Author
(19) Taherian, A.; Li, X. L.; Liu, Y. Q.; Haas, T. A. BMC Cancer 2011,
11, 293−308.
Notes
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The authors declare no competing financial interest.
ACKNOWLEDGMENTS
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We thank the Singapore National Research Foundation (R-
279-000-323-281), the Research Grants Council of Hong Kong
(HKUST2/CRF/10 and N_HKUST620/11), and the Institute
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dx.doi.org/10.1021/ja302369e | J. Am. Chem. Soc. 2012, 134, 9569−9572