Biomedical Engineering Reference
In-Depth Information
of
D
f2
equal 1.78902 to
D
f3
equal to 2.4304, the binding rate coefficient increases by a factor of
3.03 from a value of
k
2
equal to 1.5596 to
k
3
equal to 4.7240. Increases in the degree of hetero-
geneity or the fractal dimension on the electrochemical biosensor surface and in the binding
rate coefficient are once again in the same direction.
Uno et al. (2007
) recently developed a peptide-nucleic acid(PNA)-modifiedIS-FET-basedbiosen-
sor that they have used for the direct detection of DNA hybridization. These authors report that their
IS-FET based biosensor uses the change in the surface potential on the hybridization of a negatively
charged DNA. They explain that the use of PNA in their system permits the highly specific and
selective binding at low ionic strength.
Uno et al. (2007)
point out that IS-FET based biological
sensors are attractive in the sense that they are of small size and weight, provide a fast response,
are portable, can be mass produced at a low cost, and are highly reliable. They further report that
IS-FET-based DNA sensors have exhibited potential in clinical and research applications.
Uno et al. (2007)
report that the IS-FET can detect surface potential changes due to the surface
adsorption of charged molecules in an aqueous environment (Souteyrand et al., 1997; Berney
et al., 2000; Frits et al., 2002; Kim et al., 2004; Li et al., 2004).
Uno et al. (2004)
and
Ohtake
et al. (2004)
have shown that the hybridization of an immobilized PNA with a complementary
DNA induces a decrease in the saturation current and a positive shift in the threshold voltage.
Figure 11.10a
shows the binding of 5
m
M target DNA2 (complementary to CYP2C9*2) in
solution to CYP2C9*2 used as a probe and immobilized on a SPR biosensor surface (
Uno
et al., 2007
). This permitted these authors to analyze the molecular recognition at the
solution-surface interface. A single-fractal analysis is adequate to describe the binding and
the dissociation kinetics. The values of (a) the binding rate coefficient,
k
, and the fractal
dimension,
D
f
, for a single-fractal analysis, and (b) the dissociation rate coefficient,
k
d
, and
the fractal dimension,
D
fd
, for a single-fractal analysis are given in
Table 11.6
(a) and (b).
In this case, the affinity,
K
(
¼
k
/
k
d
) value is 30,347.2 (an extremely high value).
Figure 11.10b
shows the binding of 5
m
M target DNA with a single base mismatch 2 (comple-
mentary to CYP2C9*2) in solution to CYP2C9*2 used as a probe and immobilized on a SPR
biosensor surface (
Uno et al., 2007
). A single-fractal analysis is once again adequate to
describe the binding and the dissociation kinetics. The values of (a) the binding rate coeffi-
cient,
k
, and the fractal dimension,
D
f
, for a single-fractal analysis, and (b) the dissociation
rate coefficient,
k
d
, and the fractal dimension,
D
fd
, for a single-fractal analysis are given in
Table 11.6
(a) and (b). In this case, the affinity,
K
(
k
/
k
d
), value is 229.54. It is of interest
to note that as the fractal dimension decreases by 2.26% from a value of
D
f
equal to
2.6306 to 2.5712 the binding rate coefficient,
k
also decreases by 56.3% from a value of
k
equal to 131.10 to 57.253. Note that changes in the binding rate coefficient,
k
, and the fractal
dimension,
D
f
, or the degree of heterogeneity on the sensor surface are in the same direction.
¼
Figure 11.10c
shows the binding of 5
m
M target complementary DNA (complementary to
CYP2C9*2) in solution to CYP2C9*2 used as a probe with a single mismatch (CYP2C9*1)
