Biomedical Engineering Reference
In-Depth Information
Using the mercaptopropionic acid (MPA)-capped CdTe QDs as the object, the
effects of capping stabilizer, the value of pH, and coexisted chemicals on electro-
chemical responses of QDs were investigated in detail via DPV [
6
]. Three DPV
peaks (A1 at 0.36, A2 at 0.68, and A3 at 0.84 V) could be observed in the MPA-
capped CdTe QDs solution, which indicated that three electrochemical processes
existed in the single scan. And the conclusion could be presented as the following:
• Different stabilizers showed little effects on the existence of A1.
• The value of pH showed important effect on DPV response of the MPA-capped
CdTe QDs. A1 only existed in a pH range from 5.2 to 8.0 with the maximum
response at pH 6.0. A2 and A3 merged with each other simultaneously in pH
6.6 and became one peak completely with pH value higher than 7.0.
• Coexisted chemicals showed different effects on DPV response of MPA-capped
CdTe QDs. Electroinactive chemicals, like chlorobenzene, showed little effect
on DPV response. ECL coreactant, such as oxalic acid, hydrogen peroxide, and
persulfate, also showed little effect on A1 process. Magnesium nitrate could
dramatically suppress all the processes A1, A2, and A3, while potassium nitrate
had little effect on A1.
Recently, Amelia et al. [
7
] systemically summarized the electrochemical prop-
erties of CdSe and CdTe QDs. By utilization of the most common electrochemi-
cal methods such as voltammetric methods and spectroelectrochemistry, they fully
investigated the electrochemical studies of core and core-shell semiconductor
nanocrystals of spherical shape. The results of representative studies were carried
out taking CdSe and CdTe as examples. Different techniques by different groups
were compared in order to attempt an interpretation of sometimes contradictory
results.
As new type of QD, graphene QDs have been widely studied nowadays. As
back in 2004, Compton and coworkers [
8
] have fully investigated the electrochem-
ical characteristics of highly ordered pyrolytic graphite (HOPG) and found that the
edge plane sites/defects of the HOPG were the predominant electrochemical active
sites. Later, Daniel's group and Robert's group studied the electrochemical behav-
ior of monolayer graphene sheets, respectively, whose results were both published
in ACS Nano sequentially. Daniel's [
9
] group first performed electrochemical
studies of individual monolayer graphene sheets derived from both mechanically
exfoliated graphene and CVD graphene. They concluded that the electron transfer
rates of graphene electrodes are more than tenfold faster than the basal plane of
bulk graphite, which could be contributed to the presence of corrugations in the
graphene sheets. By investigating the electrochemical properties of CVD-grown
graphene electrodes in FcMeOH electrolyte at different scan rates, they found that
the effective surface area of the graphene electrode was less than the geometric
area of this electrode, indicating that the redox reactions occurred predominantly
on a clean graphene surface. Kinetic parameter of
Δ
E
p
(after proper resistance
correction) ranged from 68.6 to 72.6 mV and increased at higher scan rate, indica-
tive of quasi-reversible kinetics in the system, which was directly proportional to
the reciprocal of the square root of scan rate,
v
−
1/2
(Fig.
5.2
).
