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qualitatively different fluorescence patterns when excited at 365 nm
(Fig. 5). Qualitatively different fluorescent responses were observed
even in cases where the fluorophore emission ratios indicate some
degree of fluorophore quenching from introduction of the analyte.
The fact that each vertical column looks different means that each
analyte has a different pattern of responses with the fluorophores
investigated. Efforts to translate this qualitative observation into a
quantitative, selective detection system are underway.
In summary, reported herein is the development of highly
efficient non-covalent energy transfer in g-cyclodextrin cavities
between toxic energy donors and fluorescent energy acceptors.
This energy transfer has a number of advantages compared to
previously-developed systems, including: (a) high sensitivity (as
low as 5.9 ppm for compound 2); (b) ease of tunability; and (c)
widespread applicability to two classes of highly toxic compounds.
The development of a full array-based detection system, and a
detailed investigation of the energy transfer mechanism, are
underway and the results will be reported in due course.
This research was funded in part by a grant from the Gulf of
Mexico Research Initiative (GOMRI).
Fig. 4 Decreased excimer emission of compound 2 in the presence of increasing
amounts of fluorophore 9 (360 nm excitation; 10 mM g-cyclodextrin; 39.6 mM
compound 2).
Table 3 Limits of detection for all analytes with fluorophores 8–10 (all values
given in parts per million (ppm))
1
2
3
4
5
6
7
a
a
a
a
8
9
10
5.9
104
61
31
83
55
43
32
12
a
a
32
9.8
a
b
b
b
a
Efforts to calculate limits of detection led to nonsensical values
in these cases. Current efforts are focused on solving this problem.
Limits of detection were not calculated in these cases because no
Notes and references
b
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The sensitivity of this method was determined by quantifying the
limits of detection for all analyte–fluorophore combinations,19
and the results are shown in Table 3. The limits of detection are
defined as the amount of analyte necessary to observe a signal
that is distinguishable from the baseline (see ESI† for details).20
The limits of detection for compounds 2 and 5 are below the
FDA-recommended concentration limits, thus providing a useful
mechanism for the detection of these highly toxic analytes.
Selectivity in the detection of toxic PAHs and PCBs can be
accomplished using array-based detection. Such detection systems
have also been referred to as ‘‘chemical noses,’’ and have been used
successfully by a number of research groups.21 Array-based detection
generally requires exposure of an analyte to a receptor array.
Statistical analyses of the resulting array of signals then lead to the
selective detection of particular analytes.
Preliminary efforts towards developing an array-based detec-
tion system have yielded promising results. Using the three
different fluorophores (compounds 8–10) in combination with
10 mM g-cyclodextrin, each analyte (PAH or PCB) displayed
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14 S. Hamai, J. Mater. Chem., 2005, 15, 2881.
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Fig. 5 Photograph of a preliminary array using 10 mM g-cyclodextrin (excitation
at 365 nm with a hand-held TLC lamp).
c
This journal is The Royal Society of Chemistry 2013
Chem. Commun., 2013, 49, 4821--4823 4823