524
Chemiluminescence and Bioluminescence, Analysis by
3
Electrochemiluminescence
Chemical reactions at the surface of an
electrode can also produce excited-state
species that decay to the ground state and
emit
light
(electrochemiluminescence).
Ruthenium(II) tris(bipyridyl) undergoes
an electrochemical reaction with tripropy-
lamine to produce a strongly reducing
tripropylamine radical and a strongly
oxidizing ruthenium(III) species at the
electrode surface (Fig. 3). These react to
regenerate ruthenium tris(bipyridyl) in
an electronically excited state that de-
cays to the ground state and emits light
at 620 nm. Suitably derivatized ruthe-
nium(II) tris(bipyridyl) molecules are ef-
fective labels (detection limit 200 fmol/L)
in nucleic acid assays of different types.
NH
NH
O
O
Y
X
(a)
H
2
O
2
+ Catalyst
Y
X
COO
COO
+
N
2
+
H
2
O
+
Light
N
NH
NH
O
O
(b)
H
2
O
2
+ Catalyst
N
COO
COO
+
N
2
+
H
2
O
+
Light
OH
Ph
OH
Ph
Cl
O
Cl
Cl
CO
2
H
2
O
2
+ Fluorophore
Cl
O
Cl
Cl
+
CO
2
+
Light
(c)
O
3
+
NO
O
2
+
NO
2
+
Light
(d)
N
Me
CO
O
+
x
H
2
O
2
/HO
N
Me
O
O
+
+
Light
(e)
Fig. 1
Examples of chemiluminescent reactions. (a) Luminol X
=
H, Y
=
NH
2
;
isoluminol, X
=
NH
2
,Y
=
H, (b) 8-hydroxy-7-phenyl-pyrido[3,4-d]pyridazine-
1,4(2H, 3H) dione, (c) bis(2,4,6-trichlorophenyl) oxalate, (d) ozone–nitric oxide,
(e) acridinium aryl ester, (f) CSPD, (g) siloxene, (h) lophine, and
(i) lucigenin.
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