632.8 nm lex is equal to or better than comparable cyanine dyes.18
Reporters such as these yield strong unique spectra that are
extremely distinctive, allowing facile detection within any real
sample matrix. To the best of our knowledge this is the first report
of such a vibration, encoded within a strongly SERRS active
molecule. This application significantly expands the range of
reporters resonant at longer, biologically compatible, wavelengths
and will allow this rapidly developing technique to reach its
potential in multiplexed analysis.
Notes and references
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7 H. A. Schmidt, Synthesis, 1980, 961–994.
Fig. 4 Direct SERRS intensity comparison on KlariteTM gold surface
(20 mW, 632.8 nm, 1 s): (a) red SQ2, (b) blue 2,4-bis[(3,3-dimethylindolin-
8 A. Trebs and K. Jacob, Angew. Chem., Int. Ed. Engl., 1965, 4, 694.
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10 G. E. Sprenger and W. J. Zeigenbein, Angew. Chem., Int. Ed. Engl.,
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2-ylidine)methyl]squaraine SQ6, (c) green: Cy5TM
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D. Graham, Small, 2007, 3, 1593–1601.
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and W. E. Smith, Chem, Commun., 1998, 1187; (b) G. M. McAnally,
C. McLaughlin, R. Brown, D. Robson, K. Faulds, D. R. Tackley,
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SERRS spectra that possess a number of vibrational bands in
the region 400–1300 cm21 making these compounds excellent
candidates for SERRS multiplexing.{ These compounds are
currently being developed as longer wavelength fluorescent labels
in proteomics20 thus the application to SERRS is significant both
in terms of sensitivity and potential simultaneous multiple target
identification. For further information on the synthesis (and
application to proteomics) of these types of dyes readers are
referred to the work of Lackowicz and Terpetschnig.14,21
A direct comparison of the SERRS intensity from SQ2, SQ6
and Cy5TM is shown in Fig. 4. The dyes were deposited from
standard solutions onto
a commercially available SERRS
substrate (KlariteTM) that has been shown to have even enhance-
ment across the active area.5
In conclusion, we have shown how strong SERRS spectra can
be obtained from the squaraine chromophore. Sensitivity using
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Chem. Commun., 2008, 567–569 | 569