Biomedical Engineering Reference
In-Depth Information
nanocrystal species (CdS
·−
) and coreactants (S
2
O
8
2
−
or H
2
O
2
). The corresponding
ECL processes were as follows [
38
]:
S
2
O
8
2
−
as coreactant:
CdS QDs
+
ne
−
→
nCdS
·−
(4.17)
S
2
O
8
2
−
+
e
−
→
SO
4
2
−
+
SO
4
·−
(4.18)
CdS
·−
+
SO
4
·−
→
CdS
∗
+
SO
4
2
−
(4.19)
CdS
∗
→
CdS
+
H
ν
(4.20)
H
2
O
2
as coreactant:
O
2
+
H
2
O
+
2e
−
→
OOH
−
+
OH
−
(4.21)
2CdS
·−
+
OOH
−
+
H
2
O
→
3OH
−
+
2CdS
∗
(4.22)
2CdS
·−
+
H
2
O
2
→
2OH
−
+
2CdS
∗
(4.23)
CdS
∗
→
CdS
+
H
ν
(4.24)
Next, we studied the enhancement ECL effect of 3-aminopropyl-triethoxysilane
(APS) on the CdSe QDs in aqueous solution by conjugating APS to the CdSe
QDs/carbon nanobute-chitosan (CNT-CHIT) composite film [
10
]. In the presence
of reactive amine groups, APS can facilitate the radical generation and electron-
transfer processes during the ECL reaction. After the addition of K
2
S
2
O
8
as core-
actant, APS can catalyze the reaction of CdSe QDs with K
2
S
2
O
8
based on the
following mechanism:
CdSe QDs
+
ne
−
→
nCdSe
·−
(4.25)
S
2
O
8
2
−
+
RC
3
H
7
-NH
2
→
SO
4
2
−
+
SO
4
·−
+
RC
3
H
7
-NH
+·
(4.26)
2
CdSe
·−
+
SO
4
·−
→
CdSe
∗
+
SO
4
2
−
(4.27)
CdSe
∗
→
CdSe
+
HV
(4.28)
However, most of the traditional QDs are made of heavy metal ions (e.g., Cd
2
+
),
which may result in potential toxicity that hampers their practical applications.
Therefore, systematic cytotoxicity research of QDs is of critical importance for their
practical biological and biomedical applications, and a large amount of studies have
been carried out for this purpose [
39
-
41
]. During the synthesis process, the syn-
thetic methods and surface modifications of QDs will greatly affect their biotoxicity.
QDs prepared via the organometallic route and aqueous route were quite different
with the surface properties. In contrast to the presence of hydrophobic ligand mol-
ecules on the surface of organic QDs, the surface of aqueous QDs are covered with
a large amount of hydrophilic molecules [
41
]. This difference of surface properties
