Chemistry Reference
In-Depth Information
N
N
HO
3
S-(H
2
C)
4
(CH
2
)
4
-SO
3
H
30
The fluorescent squaraine labels Seta-670-mono-NHS and Seta-635-NH-
mono-NHS were covalently attached to antibodies and used in a
surface-enhanced
immunoassay
[
98
]. In the fluorescence intensity and lifetime changes determined
for a surface that had been coated with silver nanoparticles, both labeled com-
pounds exhibited a 15-20-fold fluorescence enhancement on the silver-coated
surface compared to that on the noncoated surface. In addition, the fluorescence
lifetime decreased drastically for both labels on silver-coated surfaces. The fluores-
cence signal enhancement obtained for the two dyes exceeded those previously
recorded for rhodamine red-X and Alexa 647 labels.
The photophysical properties of the NIR fluorescent label SeTau-665 (SETA
BioMedicals) were investigated on a plasmonic platform of self-assembled colloi-
dal structures of silver prepared on a semitransparent silver film [
99
]. A SeTau-
665-based
immunoassay
was performed on this platform and a control glass slide.
The fluorescence properties of this label substantially change because of plasmonic
interactions. While the average brightness increase of SeTau-665 in ensemble
measurements was about 70-fold, fluorescence enhancements up to 400-times
were observed on certain “hot spots” for single molecule measurements. The
intensity increase is strongly correlated with a simultaneous decrease in fluores-
cence lifetime in these “hot spots”. The large increase in brightness allows the
reduction of the excitation power resulting in a reduced background and increased
photostability. The remarkable fluorescence enhancements observed for SeTau-
665 should allow to substantially improve single molecule detection and help to
lower the detection limits in sensing devices.
8 Concluding Remarks
The process of combining cyanine and squaraine dyes by encapsulation, or covalent
or noncovalent attachment with macrocyclic hosts, macromolecules, and micro- or
nano-particles is a promising way to design novel probes and labels with substan-
tially improved properties and for the development of advanced fluorescence-based
assays. Nevertheless, the physicochemical properties of these dye-compositions are
strongly dependent on the dye structure as well as the nature of the host macrocycle,
macromolecule, or particle. Finally, development of new methods to synthesize
these tracers can also be considered a challenging task.
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