Biomedical Engineering Reference
In-Depth Information
Singh et al. (2008) coated the antibody-immobilized Au NPs/poly TTCA on a GCE (glassy
carbon electrode). Ag/AgCl (in saturated KCl) and a platinum (Pt) wire were used as refer-
ence and counter electrodes, respectively. The measurements were carried out in a batch-wise
mode. The authors carried out the chronoamperometric measurements at a potential of
0.4 V
applied to the HRP (horse radish peroxidase)-OPG/anti-OPG/Au NPs/poly TCCA. This per-
mitted the reduction of hydrogen peroxide added to the cell. The authors state that the basic
principle of their immunosensor is that “the added hydrogen peroxide reduced by the labeled
HRP generates a cathodic current. This current decreases with the addition of free-OPG. This
is because of the competition between the free- and labeled-OPG for the active site of the
antibody” ( Rahman et al., 2004 ).
Singh et al. (2008) have confirmed the labeling of the horse radish peroxide to the OPG by
recording cyclic voltagram (CV) for a HR-OPG/anti-OPG/poly TCCA modified GCE in PBS
solution. They attempted to optimize the incubation time in the 5-35 min range, and noted that
at 30-min a maximum signal is obtained. Apparently, the biosensor surface was saturated with
labeled antigens. Therefore, a 30-min incubation time was used for further studies.
Similarly, a pH range of 5.5-8.5 was analyzed on their biosensor response. The authors
obtained the best response at pH 7.4. They report that after a pH of 7.4, the response is poor
(less than the maximum). The reasons are:
(a) Loss of anti-OPOG or HRP activity.
(b) The electrocatalytic reduction of hydrogen peroxide by the horseradish peroxidase may
be decreased due to poor enzyme activity. Also, the maximum response was obtained at
an applied potential of
0.4 V.
Singh et al. (2008) report that they have successfully fabricated an OPG biosensor (immuno-
sensor) by covalently immobilizing anti-OPG on the Au NPs deposited poly TTCA (5,2 0 ,5 0 ,2 00 -
terthiophene-5 0 -carboxylic acid) layer .The authors were able to apply their fabricated biosensor
to detect OPG from serum samples of OP patients. This is a seriously debilitating and
gradually-progressing disease. Any efforts spent in helping detect this disease in its early stages
will make for a better prognosis. Of course, one also has to keep in mind the simplicity and
the cost-effectiveness of this technique, especially if continuous monitoring is required.
5.10 Label-Free Antigen-Antibody Binding on a Gold Nanoparticle
Sensor Array ( Olkhov and Shaw, 2008 )
Olkhov and Shaw (2008) have recently developed a gold nanoparticle sensor array. They
used light-scattering properties to demonstrate the changes in the local refractive index of
the surface. The authors bound fibrinogen or BSA to each array spot. Scattered radiation
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