Biomedical Engineering Reference
In-Depth Information
Fig. 5.6
The organization of oligonucleotide/DNA-cross-linked arrays of CdS nanoparticles and
the photoelectrochemical response of the nanoarchitectures. Reproduced with permission from
Ref [
50
]. Copyright 2001, Wiley
with 3 and with a solution containing 2-functionalized CdS nanoparticles resulted
in an array with a controlled number of CdS nanoparticle generations. The photo-
current follows the absorbance spectrum of the CdS nanoparticles, and it increases
with increasing number of generations of cross-linked particles. As we use a sac-
rificial electron donor as hole scavenger, we attribute the resulting photocurrent
to the injection of conduction-band electrons into the electrode. The photocurrent
can be switched “on” and “off” by pulsed irradiation of the arrays. The mechanism
of photocurrent generation probably involves the photoejection of conduction-
band electrons of CdS particles in contact with or at tunneling distances from the
electrode.
The conductivity of DNA has been a subject of extensive controversy [
51
], and
it is accepted that DNA exhibits poor conductivity [
52
]. However, the conduc-
tivity of DNA could be controlled by appropriate ordering of the base sequence
[
53
] or by the incorporation of redoxactive intercalators into dsDNA [
54
]. CdS
nanoparticle/DNA conjugates was immobilized on gold surfaces and the effects of
intercalators and the applied potential on the photoelectrochemical features of the
system was described in Fig.
5.7
[
55
]. The results demonstrate that the resulting
photocurrent can be reversibly switched between cathodic and anodic directions
by controlling the redox state of the intercalated species. The intercalation of dox-
orubicin into the dsDNA here results in a fivefold higher anodic photocurrent. The
intercalation of methylene blue into the dsDNA here results in enhanced cathodic
photocurrent while the intercalation of oxided methylene blue in enhanced anodic
photocurrent.
