Biomedical Engineering Reference
In-Depth Information
Ru
(
bpy
)
3
3
+
+
C
2
O
4
2
−
→
Ru
(
bpy
)
3
2
+
+
C
2
O
4
·−
(4.2)
C
2
O
4
·−
→
CO
2
·−
+
CO
2
(4.3)
Ru
(
bpy
)
3
3
+
+
CO
2
·−
→
Ru
(
bpy
)
3
2
+∗
+
CO
2
(4.4)
Ru
(
bpy
)
3
2
+
+
CO
2
·−
→
Ru
(
bpy
)
3
+
+
CO
2
(4.5)
Ru
(
bpy
)
3
3
+
+
Ru
(
bpy
)
3
+
→
Ru
(
bpy
)
3
2
+∗
+
Ru
(
bpy
)
3
2
+
(4.6)
Ru
(
bpy
)
3
2
+∗
→
Ru
(
bpy
)
3
2
+
+
H
ν
(4.7)
Other common coreactants include peroxydisulfate (persulfate, S
2
O
8
2
−
), tri-
n-propylamine (TPrA) and other amine-related derivatives, hydrogen perox-
ide (H
2
O
2
). The main organic luminants contain luminal, tris(2,2′-bipyridine)
ruthenium(II)
Ru
(
bpy
)
2
+
and their derivatives.
3
4.1.1 ECL of Semiconductor QDs
The first QDs ECL behavior was studied by Bard et al. In 2002, they first reported
the silicon QDs ECL property [
1
]. The Si QDs have the ability to store charge
in
N
,
N
′-dimethylformamide and acetonitrile, which can subsequently lead to light
emission upon electron and/or hole transfer. This quality provides electrochemi-
cally sensitive optoelectronic properties. In 2006, they observed the ECL emis-
sion from silica NPs in aqueous solution [
25
]. By using S
2
O
8
2
−
as the coreactant,
octadecyl-protected silica NPs deposited on indium tin oxide (ITO) showed ECL
in both anodic and cathodic sweep potentials. In the negative potential scans, the
Si NP film could produce a large ECL signal when the potential beyond
−
0.95 V.
The principle was described as follows:
S
2
O
8
2
−
+
e
−
→
SO
4
2
−
+
SO
4
−
(4.8)
SO
4
−
→
SO
4
2
−
+
h
+
(4.9)
Si
+
e
−
→
Si
−
(4.10)
Si
−
+
h
+
→
Si
+
light
(4.11)
The elemental and compound semiconductors, such as Ge [
2
], CdTe [
26
], PbS
[
27
], CdSe [
28
,
29
], and ZnS [
30
], can also generate efficient ECL. The ECL mecha-
nism of semiconductor QDs mainly depends on the annihilation or coreactant ECL
reaction. For example, PbS QDs can form oxidized (R
·+
) and reduced (R
·−
) QDs dur-
ing potential cycling. Two oppositely charged QDs can collide to yield an excited QD
