Biomedical Engineering Reference
In-Depth Information
binding of the negatively charged DNA, resulting in distinct changes in the interfacial
impedance at certain measuring frequencies. In 2000, Takahashi et al. [126] investigated
the chlorination/amination/carboxylation process on H-terminated diamond for perse-
vering and analyzing DNA clip. In 2002, Yang et al. [127] modified the nanocrystalline
diamond with alkenes and concluded that DNA bonding on diamond material would
be much better than that on other substrates. Then, several methods including chemical
reduction [128] and direct amination [129] on diamond with DNA [127], enzyme [130], and
proteins [131] were investigated by using cyclic voltammetry and other electrochemistry
methods. To understand the electrical response and the hybridization-induced changes,
the impedance data were analyzed using equivalent circuit models with constant phase
elements (CPEs). The electrochemical equivalent circuit of DNA-modified diamond film,
which was given by Yang et al. [130] and Rao et al. [132], is shown in Figure 4.20.
In the equivalent circuit,
R
s
represents the ohmic resistance of the electrolyte solution.
The paralleled resistor
R
1
and capacitor
C
dl
reflect the properties of the molecular layer and
the double layer.
R
2
and CPE (=
A
-1
(
j
ω
)
-
α
), where
A
and
α
are nonintegral, adjustable param-
eters, which describe the impedance of the space charge region of the BDD electrode.
From 2006 to 2007, Nebel et al
.
[133-135] applied the photochemistry technology to attach
alkene modules on undoped diamond and electrochemical reduction of diazonium salts
to form nitrophenyl-linker molecules on boron-doped CVD diamond [133,136,137]. Thiol-
modified single-stranded probe DNA (ss-DNA) was bonded to diamond by hetero-
bifunctional cross-linker. Then, such surfaces were exposed to fluorescence-labeled target
ss-DNA to investigate hybridization on the DNA-FET (field-effect transistor) structure.
CVD diamond growth process and photochemistry method were introduced in the arti-
cle of Nebel et al. [138], and x-ray photoelectron spectroscopy, atomic force microscopy,
fluorescence microscopy were utilized to characterize the surface with DNA. Figure 4.21
shows the EIS properties of DNA-modified nanodiamond films. The impedance shown on
Nyquist plot was detected from ss-DNA exposure to 4-base mismatched DNA and after
exposure to complementary DNA in pH 7.4 phosphate buffer containing 1 mM Fe(CN
6
)
3-
/
4-
.
The Nyquist plot, indicated discriminating hybridization of matched and mismatched
DNA. The author gave an interpretation of these results, which depended on several fac-
tors including variations of ss-DNA and double-strand DNA layers, applied external elec-
tric fields, as well as the effect of redox molecules such as Fe(CN
6
)
3-
/
4-
on the dielectric and
conductivity properties of DNA films on diamond.
R
1
R
2
R
s
C
dl
CPE
Bulk
solution
Polymer film and
double-layer
BDD space
charge layer
FIGURE 4.20
EIS equivalent circuit of DNA-modified diamond film.
