Biomedical Engineering Reference
In-Depth Information
ystyrene matrix. The potential of the working electrode was linear-
ly swept anodically while simultaneously measuring the fluores-
cence intensities as a function of time. Most intensity curves ex-
hibited a large intensity drop associated with the fluorescence
quenching due to the electrochemical oxidation of F8BT. In effect,
this was a cyclic voltammetry experiment wherein instead of the
current, the fluorescence intensity of the redox-active molecule
was being measured. Using this technique the authors were able to
determine the broad distribution in the half-wave potentials,
E
1/2
,
for the individual molecules. They extended these measurements
in a later study
134
to probe the hole-injection charging dynamics in
the individual F8BT nanoparticles. A variation on the same theme
was the study of ECL at the single-particle level.
135
Together with
the supporting electrolyte, some co-reactant tri-n-propylamine
(TPrAH) was also added. As the potential was scanned anodically,
both the F8BT and TPrAH were oxidized and the reaction between
the F8BT
+
and TPrA
•
so produced generated an excited state in the
nanoparticle, resulting in chemiluminescence. A key advantage of
ECL over photoluminescence experiments is the significantly low-
er background signal leading to higher sensitivities and spatial
resolution.
Lei, Hu and Ackerman
136
used scanning confocal fluorescence
microscopy to detect individual cresyl violet molecules (strongly
fluorescent only in the oxidized state) as these pass the confocal
volume when diffusing to and from a transparent ITO electrode
during cyclic voltammetry. In a second paper
137
, this method was
applied to immobilized cresyl violet on a clay nanoparticle-
modified ITO electrode. In this way, individual molecules could be
followed over long time periods, yielding single-molecule spectro-
electrochemical voltammograms. However, the response was con-
voluted with blinking, and no statistical analysis was presented. Xu
and co-workers
138
report on single-molecule fluorescence, follow-
ing the electrocatalytic generation of a fluorogenic product by sin-
gle-walled carbon nanotube (SWNT) deposited on ITO. The elec-
troreduction of nonfluorescent resazurin to fluorescent resorufin
during cyclic voltammetry was detected by total internal reflection
microscopy. Statistical and single-molecule kinetic analysis re-
vealed the catalytic mechanism and the heterogeneous reactivity of
discrete nanoscopic sites on the SWNT.
Search WWH ::
Custom Search